Method, use of adapted optotypes and device for determining the visual acuity characteristics of a subject

Abstract

Procedure for determining the visual acuity characteristics of a subject who has at least one astigmatic refractive error, comprising the following steps: - Providing refractive error data of the subject, wherein the refractive error data includes at least one axis position of a required optical cylinder correction; - Selecting a preferred direction (V1; V2) such that this preferred direction (V1; V2) either corresponds to the axis position assigned to the optical cylinder correction, or is rotated by 90° to this axis position, or the preferred direction (V1; V2) is derived from wavefront data using a point spreading function; - Creating a visual effect at least in the selected preferred direction; - Display of at least one adapted optotype which has a directional feature, wherein the adapted optotype is displayed oriented such that its directional feature is arranged parallel to the preferred direction (V1; V2); and - Determining the visual acuity characteristics of the subject for the selected preferred direction (V1; V2) taking into account at least one dimension of the directional feature of the adapted optotype as well as the applied optical effect; where a hatched area is used as the adapted optotype, in which the hatching lines are arranged perpendicular to the selected preferred direction (V1; V2); and / or in which, in addition to the adapted optotype, at least one further optotype is displayed, the gray value of which corresponds approximately to an average gray value of the adapted optotype, and the subject is asked to distinguish the displayed optotypes from each other as part of a visual task.

Description

[0001] The invention relates to a method, the use of adapted optotypes and a device for determining the visual acuity characteristics of a subject.

[0002] Determining visual acuity, or the visual sharpness characteristic, of a subject with a refractive error, particularly astigmatic refractive error, is a central task in optometry. Astigmatic refractive error can be compensated for by providing and / or applying a cylinder correction lens in addition to any necessary spherical correction.

[0003] Known methods for determining the visual acuity of a subject with astigmatic refractive error are often lengthy, costly, and / or prone to error, as they frequently rely on active feedback from the subject. Furthermore, determining visual acuity requires compensating for the subject's astigmatic refractive error by applying optical cylinder and sphere correction, for example, using a phoropter or trial frame.

[0004] Holding the optical cylinder correction in front of the trial frame or phoropter is cumbersome and requires space, which is why combining the trial frame or phoropter with other devices such as an eye tracker is cumbersome.

[0005] Without providing the subject with the required cylinder correction in the optical unit used, no compensation for astigmatic refractive error takes place.

[0006] Therefore, it is often impossible to determine any visual acuity or only a distorted visual acuity in the relevant range in the test subject, especially if the test subject has a significant cylinder error.

[0007] Document US 2017 / 0100031 A1 discloses a refraction device for determining a refractive endpoint in order to provide a test subject with corrective optics. The device comprises an adjustable optical system that provides corrective optics to the test subject and an adjustable viewing target arranged along an optical path so that it can be viewed by the test subject through the adjustable optical system. The adjustable viewing target includes a direction indicator that is synchronously connected to at least two corrective optics presented to the test subject.

[0008] Document US 5914772 A discloses a device and method for testing eyes. This method is objective and can be performed by a technician, so that only trained personnel are required to interpret the final prescription. The method includes obtaining autorefractor, corrected autorefractor, and autolensometer results; calculating the sphere; performing a red-green test; calculating the cylinder and axis; determining the minimum cylinder strength; determining the final sphere; and recording all data. The calculation of the sphere and the calculation of the cylinder and axis do not rely on the subjective interpretation of the subject's responses.

[0009] The subsequently published document DE 10 2021 202 442 A1 discloses a method for determining the sensitivity of at least one eye of a subject. This involves determining a subjective refraction result for at least one eye of the subject. During the determination of the subjective refraction result, a first visual acuity of at least one eye is determined for a first applied refraction. During the determination of the subjective refraction result, a second visual acuity of at least one eye is determined for a second applied refraction, the second applied refraction being different from the first applied refraction. The sensitivity of at least one eye is then determined taking into account the first and second visual acuity values ​​for the first and second applied refractions.

[0010] The invention is based on the objective of determining visual acuity characteristics of test subjects with astigmatic refractive error simply and reliably.

[0011] This problem is solved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims.

[0012] One aspect concerns a method for determining the visual acuity characteristics of a subject who exhibits at least one astigmatic refractive error. This involves providing the subject's refractive error data, which includes at least one axis position of a required optical cylinder correction. A preferred direction is then selected such that this direction either corresponds to the axis position assigned to the optical cylinder correction or is rotated 90° relative to this axis position. Alternatively, the preferred direction can be derived from wavefront data using a point spread function. An optical effect is then applied, at least in the selected preferred direction.At least one adapted optotype is displayed, which has a directional feature. The adapted optotype is displayed oriented so that the directional feature is parallel to the preferred direction. Finally, the subject's visual acuity characteristics are determined for the selected preferred direction, taking into account at least one dimension of the directional feature of the adapted optotype and the applied optical effect.

[0013] The visual acuity characteristics of the subject can be determined for one eye, for each eye individually (monocularly), or for both eyes together (binocularly). Preferably, the visual acuity characteristics are determined monocularly for each eye individually.

[0014] The subject has astigmatic refractive error and therefore requires optical cylinder correction, which corrects and / or reduces their refractive error. Individuals with astigmatic refractive error very often also require optical sphere correction, which is combined with the optical cylinder correction. These optical corrections can be integrated, for example, into spectacle lenses, contact lenses, and / or intraocular lenses for the subject.

[0015] The applied optical effect can be achieved by placing an optical correction (such as a lens) in front of the subject's eye. The optical correction manipulates the light entering the subject's eye. Thus, the optical corrections can correspond to a projected optical effect, particularly one with a spherical and / or cylindrical optical effect.

[0016] To select the preferred direction, the subject's refractive error data is first required. This data may have been obtained, for example, through subjective and / or objective refraction. The data may also be available as prescription information for the subject. The procedure for determining visual acuity may be integrated into, or performed after, an objective and / or subjective refraction test.

[0017] The refractive error data includes at least the axis of the required optical cylinder correction. In addition, the refractive error data may also include the strength of the required optical cylinder correction. Furthermore, the refractive error data may include a required optical sphere correction, the required optical cylinder correction, and the axis of the cylinder associated with that cylinder correction.

[0018] Alternatively, the visual impairment data can be based on a wavefront analysis and on wavefront data obtained in this way.

[0019] The preferred direction is selected based on the refractive error data, particularly the assigned axis position. The preferred direction can be either the axis position itself or a direction rotated 90° to that axis position.

[0020] If the refractive error data is based on wavefront data, the preferred direction can also be derived from this wavefront data using a point spread function. The preferred direction can be derived from a point spread function calculated based on the wavefront data. Here, the direction and / or axis of the smallest extent of the point spread function can be selected as the preferred direction. Alternatively, the direction of least confusion can be selected, for example, the direction of the smallest standard deviation of the point spread function.

[0021] The axis is typically located in a plane approximately perpendicular to a selected viewing direction of the subject. This viewing direction can be, for example, the subject's viewing direction in the user position, as defined in the relevant standards. The axis is located and / or defined in a plane approximately perpendicular to the user position. In particular, the axis may be located in a plane in which a spectacle lens and / or a contact lens is to be positioned for the subject. Thus, the axis may coincide with an axis of an optical cylinder correction that is to be integrated into a spectacle lens and / or a contact lens for the subject.

[0022] If the axis position is selected directly as the preferred direction, the preferred direction is arranged approximately in the first principal section of the required optical cylinder correction and additionally approximately perpendicular to the subject's line of sight.

[0023] If a direction rotated 90° relative to the axis is selected as the preferred direction, this 90° rotation occurs within a plane approximately perpendicular to the subject's line of sight. The selected preferred direction can be located approximately in the second principal section of the required optical cylinder correction and also be approximately perpendicular to the subject's line of sight.

[0024] Once a preferred direction has been selected as described, the optical effect is applied, at least in that preferred direction. For example, a rotationally symmetric optical lens can be used, such as an optical sphere correction. Specifically, the optical sphere correction that, according to the refractive error data, at least partially corrects the subject's refractive error in the selected preferred direction can be applied.

[0025] If the preferred direction is the axis of the required optical cylinder correction, i.e., the first principal section of the cylinder correction, then, for example, an optical sphere correction of the strength that exactly corresponds to the required sphere correction contained in the refractive error data can be used as the optical effect, without taking into account the cylinder error of the subject.

[0026] If the preferred direction is the one rotated 90° to the axis position, i.e., the second principal section through the cylinder correction, then, for example, an optical sphere correction with a strength can be applied as the optical effect. This strength results from the sum of the sphere correction stored in the refractive error data plus the cylinder correction stored there (e.g., both specified in diopters). The signs of the required sphere correction and the required cylinder correction must be taken into account when calculating the sum.

[0027] If the refractive error data includes a required sphere correction of s and a required cylinder correction of z (sometimes abbreviated as c), then a correction with the value s can be applied as the optical effect for the first principal meridian, and one with the value s+z for the second principal meridian.

[0028] The optical effect can be applied by presenting it to at least one of the subject's eyes. This can be done, for example, by physically presenting the respective optical lens, e.g., using a trial frame and / or a refraction unit. Alternatively, the optical effect is not applied physically, but can be simulated using wavefront simulation. The precise method of application can therefore depend on the refraction unit used.

[0029] To achieve the desired optical effect, at least in the selected preferred direction, a spherical optical effect is preferably used, for example, a rotationally symmetric lens. This produces the desired optical effect not only in the selected preferred direction but even across the entire sphere. A spherical optical effect can also be simulated virtually.

[0030] With this optical effect, the refractive error of the subject can be at least partially corrected, at least for the selected preferred direction.

[0031] It is noteworthy that no optical cylinder correction is required to determine visual acuity characteristics. According to the procedures, it is sufficient to determine the visual acuity characteristics by applying and / or holding, for example, a purely optical sphere correction, without needing an optical cylinder correction.

[0032] Applying an optical spherical correction is usually easier than applying an optical cylindrical correction, for example, because spherical correction does not require consideration of the axis position. This simplifies the process by eliminating the need for optical cylindrical corrections.

[0033] Visual acuity characteristics can be determined, for example, by ascertaining at least one visual acuity for the applied optical effect, and / or the subject's sensitivity, and / or a visual acuity-correction value pair. A visual acuity-correction value pair contains information about the subject's visual acuity when the corresponding correction is applied as an optical effect for at least the selected preferred direction. Therefore, the visual acuity-correction value pair can also additionally include the corresponding preferred direction.

[0034] Visual acuity testing based on optotypes, such as visual acuity charts, is generally known. However, according to the invention, not (only) normal and unadapted standard optotypes are used, but rather adapted optotypes that are tailored to the selected preferred direction and thus to the refractive error of the test subject. Optotypes with a directional feature are suitable for this purpose.

[0035] The adapted optotype here features a directional indicator that the subject is expected to identify during a visual task. Optotypes with directional indicators are generally known, such as Landolt rings or the Snellen E. However, Landolt rings, for example, are typically oriented so that the gap of the respective ring is located at exactly 0°, 90°, 180°, etc.

[0036] In contrast to the generally accepted arrangement of the gap in the Landolt rings as optotypes, adapted optotypes are now used whose directional feature is positioned exactly and / or as closely as possible parallel to the selected preferred direction. If, for example, the axis position associated with the required optical cylinder correction is exactly 12°, or generally exactly the angle α, and this axis position is selected as the preferred direction, the adapted optotype is positioned so that its directional feature is displayed exactly at the angle 12°, or generally at the angle α. This precisely aligns the optotype with the selected preferred direction, for which the applied optical sphere correction effectively corrects the subject's refractive error.

[0037] The positioning of the directional feature of the fitted optotype in the preferred direction allows the subject to recognize this feature even if their astigmatism is not fully corrected, i.e., not also cylindrically corrected. Even if the subject cannot see the fitted optotype perfectly sharply because their astigmatism is not corrected by optical cylinder correction, they can still recognize at least the directional feature if their visual acuity is sufficiently adequate. Thus, the fitted optotype allows the subject to recognize at least the directional feature if their vision is optimally and / or at least sufficiently corrected in the preferred direction by the applied optical effect.

[0038] Finally, the subject's visual acuity for the selected preferred direction can be determined by considering at least one dimension of the directional feature of the fitted optotype. The visual acuity can be determined in the usual way, i.e., depending on the dimension of the directional feature that the subject can just barely perceive and / or identify under the applied optical effect.

[0039] To determine the dimension required for visual acuity calculation, the subject can be shown several adapted optotypes sequentially and / or simultaneously, differing in one dimension of the directional feature. As part of at least one visual task, the subject can be asked to identify at least one adapted optotype.

[0040] Within the context of a visual task and / or a sequence of visual tasks, at least one adapted optotype can be displayed progressively smaller, so that the visual tasks become progressively more difficult. Alternatively, the differently sized adapted optotypes can be displayed simultaneously. This allows researchers to determine the maximum size of the directional feature at which the subject can still recognize the adapted optotype.

[0041] The refractive error data required for the procedure can, for example, correspond to the best correction and / or refraction the subject needs to correct their refractive error. Additionally or alternatively, the refractive error data can also deviate somewhat from the best required optical corrections. For example, the refractive error data can correspond to the data determined for the subject based on an objective refraction measurement. The objectively determined refraction data, at least in the axis position determined in this process, usually correspond very closely to the axis position of the cylinder correction actually required by the subject.

[0042] As an optical effect, in addition to, for example, the best correction, a slightly "blurred," or altered, optical correction can also be applied, for instance, when determining the subject's sensitivity. In this case, intentionally "worsened" refractive error data can also be used.

[0043] In one variation, the applied optical effect can be completely independent of the subject's refractive error data. Here, the dimension of the directional feature of the displayed, adjusted optotype can be kept constant, and instead, the applied optical effect for this constant dimension can be varied until the subject can (or can no longer) recognize the directional feature of the adjusted optotype. In this way, a visual acuity-correction value pair can be determined that is independent of the (subjectively and / or objectively determined) optimal correction.

[0044] In principle, visual acuity can be determined most accurately as a visual acuity characteristic for the selected preferred direction if the optimal optical correction required by the subject in the selected preferred direction is used as the optical effect.

[0045] This method allows for the determination of a subject's visual acuity characteristics, such as visual acuity, without requiring the use of optical cylinder correction devices. Instead, customized optotypes are used, precisely aligned with the axis of the required cylinder correction, thus eliminating the need for the application of optical cylinder correction devices. This enables the determination of visual acuity characteristics using, for example, a less expensive device that cannot itself apply optical cylinder correction.

[0046] Furthermore, the method allows the refraction unit to be combined with additional devices, as more space is available for these additional devices if the option of applying the required cylinder correction is not needed. For example, a refractometer, particularly an autorefractor, can be used as the refraction unit to apply the optical effect.

[0047] In a visual acuity test, the refractive error of the subject can only be corrected for the selected preferred direction, but not for the principal section perpendicular to it for the required cylinder correction.

[0048] As adapted optotypes, those whose lowest spatial frequencies lie in the direction of the most uncorrected principal meridian, i.e., are aligned parallel to it, can be used. Alternatively or additionally, the highest spatial frequencies of the optotypes used can lie in the direction of the best-corrected principal meridian, i.e., are aligned parallel to it.

[0049] When using objective measurements and / or combined objective and subjective measurements to provide the refractive error data, the axis position, i.e., the orientation, can be directly derived from the objective data, as objective axis measurements are usually very reliable. The objectively measured cylinder, i.e., the objectively measured required optical cylinder correction, can be reduced somewhat compared to the measured refractive error data, since the objectively measured cylinder is often not perceived in its full strength by the subject. If necessary, the spherical equivalent should be calculated before adjusting the cylinder power and used instead of the sphere when calculating the principal meridians.

[0050] According to one embodiment, the directed feature of the adapted optotype has a sequence of light and dark areas that follow one another along the preferred direction. The sequence of light and dark areas can, for example, be oriented perpendicular to the lines of a hatching pattern or perpendicular to the arrangement of the gap in a Landolt ring. Thus, perpendicular to the gap in a Landolt ring, the dark circle's edge is followed first by the light gap, and then again by the dark circle's edge. Therefore, the directed feature of a Landolt ring is arranged perpendicular to the gap. In a Snellen E, the directed feature is arranged perpendicular to the three parallel E lines. In general, the directed feature can correspond to a sequence of at least one light area followed by a dark area, preferably at least the interruption of a dark area by a light area, or conversely, at least the interruption of a light area by a dark area.The light and / or dark areas can be formed, for example, as lines and / or have edges oriented perpendicular to the preferred direction.

[0051] According to one embodiment, an unadapted standard optotype with a directional feature is provided. The standard optotype is rotated in a display plane such that its directional feature is aligned parallel to the preferred direction. Finally, the rotated standard optotype is displayed as the adapted optotype. The display can, in particular, take place on a screen within a display plane. Initially, the unadapted standard optotype is used, which is then rotated (e.g., purely computationally, without being displayed) so that it is correctly aligned with the selected preferred direction. This transforms the unadapted standard optotype into the adapted optotype. Only after this internal calculation is the adapted optotype displayed. The display plane can be, for example, the plane within which the screen can display the optotypes.The display plane is preferably arranged approximately perpendicular to the subject's line of sight and / or approximately parallel to the selected preferred direction.

[0052] By using an initially unadjusted standard optotype with a directional feature, this unadjusted standard optotype can be easily transformed into an adjusted optotype by rotating it, for example, around the center point of the standard optotype and / or around another point in the display plane. This adjusted optotype can then be adapted to any axis position of the required optical cylinder correction. Furthermore, the adjusted optotype can be scaled as desired on the display, allowing it to be shown larger or smaller depending on the current visual task being presented to the subject.

[0053] According to one embodiment, the axis position is selected as a first preferred direction, which is assigned to the optical cylinder correction and which is arranged in the first principal meridian of the required optical cylinder correction, wherein the optical effect is an optical sphere correction which corrects the refractive error of the subject in the first principal meridian according to the refractive error data, and wherein the visual acuity characteristic of the subject for this first principal meridian is determined.Alternatively or additionally, a second preferred direction is selected that is rotated 90° to the axis position and is located in the second principal meridian of the required optical cylinder correction. The optical effect applied is an optical sphere correction that corrects the subject's refractive error in the second principal meridian according to the refractive error data. The subject's visual acuity for this second principal meridian is determined as the visual acuity characteristic. If the first preferred direction is selected, the optical sphere correction applied can be precisely the one specified in the refractive error data as the required optical sphere correction.If the second preferred direction is selected, i.e., the second principal meridian, the optical sphere correction can be the sum of the optical sphere correction stored in the refractive error data plus the stored optical cylinder correction. This sum corresponds to the correction required by the subject in the second principal meridian. Thus, with the optical sphere correction selected in this way, the subject's refractive error is corrected relatively well and / or as effectively as possible, at least in the selected preferred direction, i.e., in the selected principal meridian.

[0054] In a training course, the subject's visual acuity is determined for both the first and second principal meridians of the required optical cylinder correction, and a direction-independent visual acuity is derived from this. In other words, the first preferred direction is selected, and the subject's visual acuity for the first principal meridian is determined. Similarly, the second preferred direction is selected, and the subject's visual acuity for the second principal meridian is determined. The results of the visual acuity test can initially be reported for each principal meridian. Furthermore, a direction-independent visual acuity can be derived from these two values. This direction-independent visual acuity can, for example, be used to...The values ​​may be given as the highest value obtained in the measurements, as the lowest value, as the arithmetic mean, as the geometric mean, as the harmonic mean, as the logarithmic mean, as the quadratic mean, as the cubic mean, or as a combination of selected values ​​of the aforementioned values.

[0055] According to one embodiment, visual acuity is determined for only one of the two principal meridians. In this case, a preferred principal meridian is selected. The preferred principal meridian can be the one in which the required optical correction is more strongly in the positive direction, or more strongly in the negative direction, or in which a stronger correction is required in magnitude, or in which a weaker correction is required in magnitude. Alternatively, the principal meridian whose axis is closer to the vertical can be selected, or the principal meridian whose axis is closer to the horizontal.

[0056] Visual acuity can generally be understood as the ability to recognize an object depending on its size, but also as the ability to recognize it depending on other parameters that influence its appearance, such as contrast. Visual acuity can also be a combination of the ability to recognize an object depending on its size and the ability to recognize it depending on contrast and / or other such parameters.

[0057] According to one embodiment, a Landolt ring is used as the adapted optotype, the gap of which is displayed rotated by 90° relative to the selected preferred direction. This 90° rotation of the gap to the selected preferred direction ensures that the dark-light-dark sequence across the gap of the Landolt ring is precisely aligned with the selected preferred direction. Thus, the directional feature of the Landolt ring is positioned exactly parallel to the selected preferred direction, and the visual acuity for the selected preferred direction can be easily determined.

[0058] According to one embodiment, a Snellen E is used as a customized optotype in which the connecting line linking the three parallel E lines is arranged parallel to the selected preferred direction. The directional feature of this Snellen E is the sequence of the three parallel E lines, i.e., for example, the sequence light (background), dark of the top line, light of the space, dark of the middle line, light of the space, dark of the bottom E line, and finally light of the background. This also allows for easy adaptation of the Snellen E as a standard optotype to the preferred direction and thus its use as a customized optotype.

[0059] In a training course, the adapted optotype is displayed at least once rotated 90° clockwise and at least once counterclockwise. The participant is then asked to distinguish between these two different rotated adapted optotypes as part of a visual task. For example, the participant might be asked to distinguish whether the gap in the Langolt ring faces left or right, assuming the preferred direction is oriented vertically upwards. A similar approach is used when employing the Snellen E as an adapted optotype.

[0060] According to one embodiment, a hatched area is used as the adapted optotype, in which the hatching lines are arranged perpendicular to the selected preferred direction. The hatched area can be, for example, a shape such as a circle, a rectangle, a symbol, an animal, letters, or the like. The shape is filled with hatching. Preferably, the shape has no border that could interfere with the hatching, but is simply a hatched, borderless shape. The hatching lines are displayed perpendicular to the preferred direction, since the directional feature, as the relevant feature of the optotype, is the sequence of alternating light and dark areas of the hatching. It can be advantageous if the shape itself is as uniform as possible and has few details, for example, as a circle or a square.Therefore, figures that are as simple and low in detail as possible are preferred. To adjust the orientation of the directed feature, either the entire optotype, including the hatching, can be twisted and / or rotated, or only the hatching within the constant area and / or figure. The hatching can be binary, i.e., have hard black and / or white edges, or it can have a continuous gradient. For example, a continuous hatching can have a sinusoidal intensity gradient or a similar intensity gradient.

[0061] According to one embodiment, in addition to the adapted optotype, at least one further optotype is displayed, the gray value of which corresponds approximately to an average gray value of the adapted optotype, and the subject is asked to distinguish between the displayed optotypes as part of a visual task. Instead of an optotype with an average gray value, an optotype can also be used whose hatching is not perpendicular to the selected preferred direction like the adapted optotype, but rather approximately parallel to the preferred direction. Due to the subject's astigmatic refractive error being incorrectly corrected for this hatching orientation, such an optotype appears to them as essentially gray perpendicular to the preferred direction.For example, several such gray optotypes and one adapted optotype, or conversely, several adapted optotypes and one gray optotype, can be displayed on a single screen during a visual task. The subject can be asked to identify the one of the displayed optotypes that differs from the others.

[0062] According to one embodiment, the applied optical effect is varied at least up to a limit refraction for the selected preferred direction, beyond which the subject can recognize the directional feature of the adapted optotype. The dimension of the displayed adapted optotype can be kept constant. For example, an extreme value of the refractive unit used, e.g., ±20 diopters, can be used as the starting value for the applied optical effect. Alternatively, a diopter value that deviates by a predetermined margin, e.g., ±5 diopters, from the optical sphere correction actually required according to the refractive error data can be used as the starting value. After applying the starting value, the applied optical effect is varied, e.g., continuously or in fixed steps, until the subject can (or can no longer) recognize the directional feature of the adapted optotype.The optical effect applied when recognizing the directional feature of the fitted optotype corresponds, as limit refraction, to an optical correction in which the subject has a visual acuity dependent on the dimension of the directional feature of the displayed fitted optotype. Thus, a visual acuity-refraction value pair for the preferred direction is determined as a visual acuity characteristic.

[0063] If this procedure is repeated with at least one second adapted optotype, in which the directional feature is dimensioned differently, a second visual acuity-refraction value pair can be determined, which differs from the first visual acuity-refraction value pair. From these two different visual acuity-refraction value pairs, the subject's sensitivity, for example, can be determined.

[0064] In an alternative embodiment, the dimension of the directional feature of the adapted optotype is varied at least up to a limit dimension at which the subject can still recognize the directional feature. The applied optical effect can be kept constant. For example, an optical correction can be applied that, according to the refractive error data, corrects the subject's refractive error in the selected preferred direction. For instance, an optimal optical correction determined through objective and / or subjective refraction can be used. In this alternative, the dimension of the directional feature of the adapted optotype can be varied, and it can be verified up to which limit dimension the subject can still recognize the directional feature. Visual acuity can then be determined from this limit dimension using conventional methods.The variation in the dimension of the directional feature of the fitted optotype can be achieved by displaying differently sized fitted optotypes and / or by varying the size of the displayed fitted optotype(s). This can be done within at least one visual task and / or a sequence of different visual tasks, with at least one fitted optotype being displayed within each visual task. In this way, visual acuity can be determined as a characteristic of visual acuity for the selected preferred direction. A visual acuity-refraction value pair with the corresponding preferred direction can also be determined.

[0065] If this procedure is repeated with at least one second optical effect applied in the selected preferred direction, a second visual acuity-refraction value pair can be determined, which differs from the first visual acuity-refraction value pair determined. From these two different visual acuity-refraction value pairs, the sensitivity of the subject can, for example, be determined.

[0066] In general, according to one embodiment, at least one visual acuity and / or at least one sensitivity and / or at least one visual acuity-refraction value pair can be determined as visual acuity characteristics.

[0067] Here, the sensitivity can be determined as a function of a sensitivity metric, for example, specifically for at least the selected preferred direction. Additionally, a sensitivity for the second preferred direction can also be determined, i.e., the direction rotated 90° relative to the first selected preferred direction. Alternatively or additionally, a direction-independent sensitivity can also be determined. The direction-independent sensitivity can be determined, for example, from the two sensitivities for the first and second preferred directions, or based on two direction-independent visual acuity-refraction value pairs (where, for example, the corresponding direction-independent visual acuity has been determined as an average of the visual acuity values ​​for the two preferred directions), or based on a suitable sensitivity metric that can determine a direction-independent sensitivity from at least two direction-dependent visual acuity-refraction value pairs.

[0068] According to one embodiment, the subject is presented with at least one visual task dependent on the displayed, adapted visual acuity symbol, which the subject answers while providing active and / or passive feedback. One embodiment of active feedback could be, for example, the subject verbally answering a question from an optician and / or another examiner regarding a visual task. Similarly, active feedback could be given, for example, by pressing a button and / or a mouse, with a gesture, and / or by looking. The subject's gaze can be recorded, for example, using an eye-tracking unit.

[0069] An eye-tracking unit like this can also provide passive feedback. This allows the unit to detect which optotype the subject is currently fixating on. This reveals whether the subject is subconsciously fixating on an optotype that differs from the others because they have recognized it, or whether they are unable to recognize the different optotype. Visual tasks with passive and active feedback can be combined. Ideally, the subject's feedback is recorded without intervention from an examiner. The subject can either actively input the feedback themselves, for example, using a button and / or a mouse-like controller, or it can be passively recorded.Eliminating the need for an examiner to perform the visual acuity test eliminates a potential source of error in the test: the human examiner. Furthermore, eliminating the human examiner can save costs and / or time.

[0070] According to one embodiment, the subject's visual acuity in the selected preferred direction is determined under two different applied optical effects, and the subject's sensitivity is calculated from this. For example, the visual acuity in the selected preferred direction can be determined once with the optimal and / or best optical effect for that direction, and again with a different optical effect. This second optical effect might be shifted, for example, by ±0.5 diopters relative to the best effect. The subject's sensitivity can then be determined from the two visual acuity values ​​obtained for the two different optical effects (i.e., corrections).

[0071] In principle, sensitivity can also be determined based on two visual acuity values, neither of which is obtained with the optimal correction. Using a mathematical model, the sensitivity of the eye and / or the subject can be calculated from the two obtained visual acuity values. Therefore, it is not absolutely necessary that the best correction is already known at the time of the visual acuity test.

[0072] It is not necessary to record all correction values ​​and / or visual acuity values ​​used for sensitivity measurement with the method according to the invention. For example, within the framework of an autorefractometric and / or aberrometric measurement, a first visual acuity can be determined, e.g., at a given distance from the refraction objectively determined in that measurement, and a second visual acuity can be determined, e.g., within the framework of a subsequent subjective refraction, at the best optical correction resulting from the subjective refraction.

[0073] However, two or more visual acuity values ​​can also be recorded using the method according to the invention. For example, during an autorefractometric and / or aberrometric measurement, a first visual acuity value can be determined, e.g., at the objectively determined best correction, and a second visual acuity value at a given interval. The objective refraction determined in this way can be used as the best optical correction to calculate the subject's actual visual acuity.

[0074] According to one embodiment, a subjective and / or objective refraction is performed, and the refractive error data of the subject is derived from the refractive error determined. For example, the refractive error data can be determined from an objective refraction, using the determined optimal optical corrections and the determined optimal axis position as the refractive error data. Alternatively or additionally, a subjective refraction can be performed. In this case, the refractive error data can be based on the result of the subjective refraction. Finally, the two results can also be combined, and the refractive error data can be derived from an average of the objectively determined best correction and the subjectively determined best correction.Particularly in the context of sensitivity testing, optical corrections that differ from the determined best correction can also be used as refractive error data.

[0075] In one embodiment, for example, an objective refraction measurement is first performed on the subject, and the best optical correction determined is used as refractive error data. Subsequently, a subjective refraction is performed, during which two visual acuity values ​​are determined using the method according to the invention. The sensitivity is then determined from these two visual acuity values. In particular, one visual acuity value is determined after completion of the subjective refraction based on refractive error data resulting from the subjectively determined best optical correction. In this embodiment, both an objective and a subjective refraction are performed, the subject's visual acuity is determined, and their sensitivity is determined. Only a spherical optical correction is applied for determining visual acuity. An optical cylinder correction is not required.

[0076] According to one embodiment, the subject's visual acuity is determined using the method and converted into a different visual acuity type. This conversion can be performed subsequently. Visual acuity is typically dependent on the optotype used. Since there are different methods for determining visual acuity, e.g., based on numbers or using a grating, such as FrACT, the visual acuity values ​​can depend on the measurement method used. The measurement-method-dependent visual acuity values ​​can be converted into one another. This conversion can be performed using a calibration function that carries out the desired conversion.

[0077] The calibration function can be determined using regression from a dataset containing numerous visual acuity values, and thus visual acuity types, for the same individual, obtained through different measurement methods (e.g., based on numerical values ​​and FrACT). This allows for the correlation of the two different visual acuity types and / or values ​​to be established using the dataset. In the simplest case, the calibration function can be a function of the visual acuity determined by the chosen method, calculating as its function value the visual acuity value that would have resulted from the other desired measurement method.

[0078] To improve conversion accuracy, the calibration function can depend on additional parameters, such as the person's pupil diameter prior to the visual acuity measurement, the orientation of the selected preferred direction, the fitted optotypes used, the uncorrected optical power in one or both principal meridians (e.g., the best-corrected or the most uncorrected principal meridian), other parameters of the fitted optotypes used (e.g., their contrast), or a combination of some or all of these parameters. Using the calibration function allows the visual acuity value determined by this method to be converted into a visual acuity value calculated using other methods, e.g., optotypes without a directional feature.

[0079] One aspect concerns the use of adapted optotypes, each of which has a directional feature arranged parallel to a preferred direction, which either corresponds to an axis position associated with an optical cylinder correction required by a subject, or which is rotated by 90° to this axis position, or the preferred direction can be derived from wavefront data using a point spreading function to determine the subject's visual acuity characteristics for the selected preferred direction, taking into account at least one dimension of the oriented feature of the adapted optotype.

[0080] The use of the adapted optotype can occur particularly within the framework of the procedure described above. Therefore, all statements regarding the procedure can also apply to its use, and vice versa.

[0081] One aspect concerns a device for determining the visual acuity characteristics of a subject who has at least one astigmatic refractive error. The device has a selection module that chooses a preferred direction. This preferred direction either corresponds to an axis position associated with an optical cylinder correction required by the subject or is rotated 90° from this axis position. Alternatively, the preferred direction can be derived from wavefront data using a point spread function. A refraction unit is configured to apply an optical effect to the subject, at least in the selected preferred direction. The refraction unit can, for example, be configured as an aberrometer and / or a refractometer and / or apply a rotationally symmetric lens as the spherical correction.A display module includes a display and shows at least one adapted optotype with a directional feature on the display such that the directional feature of the adapted optotype is arranged parallel to the preferred direction. A visual acuity characteristic determination module determines the subject's visual acuity characteristics for the selected preferred direction, taking into account at least one dimension of the directional feature of the adapted optotype and the applied optical effect.

[0082] The device can be used, for example, to carry out the procedure described above and / or to use the adapted optotypes described above. Therefore, all statements regarding the device also apply to the procedure and its use, and vice versa.

[0083] The dimension of the directed feature can be, for example, a distance between hatching lines, a contrast strength, a line thickness and / or a gap width.

[0084] According to one embodiment, the device includes an eye-tracking unit that tracks at least one eye of the subject when the at least one adapted optotype is displayed. The eye-tracking unit can be used to determine the subject's gaze direction and to register active and / or passive feedback from the subject as a response to a visual task.

[0085] Within the scope of this invention, the terms “essentially” and / or “approximately” may be used to include a deviation of up to 5% from a numerical value following the term, a deviation of up to 5° from a direction following the term and / or from an angle following the term.

[0086] Terms such as above, below, over, under, lateral, etc. refer - unless otherwise specified - to the Earth's reference system in an operating position of the subject matter of the invention.

[0087] The invention is described in more detail below with reference to exemplary embodiments shown in the figures. Here, identical or similar reference numerals may denote identical or similar features of the embodiments. Individual features shown in the figures may be implemented in other exemplary embodiments. The figures show: Fig. 1A Examples of displayed optotypes for determining visual acuity; Fig. 1B the one for the in Fig. 1A shows the visual impression of a subject whose cylindrical refractive error is corrected for the second principal meridian with an optical sphere correction; Fig. 1C, which is for the in Fig. 1A shows the visual impression of a subject whose first principal meridian of cylindrical refractive error is corrected with an optical sphere correction; Fig. 2A Examples of adapted optotypes for a visual task for a subject who has been corrected for the second principal meridian of his cylindrical refractive error with an optical sphere correction; Fig. 2B, which is for the in Fig. 2A shows the visual impression of a subject whose cylindrical refractive error is corrected for the second principal meridian with an optical sphere correction; Fig. 3A Examples of adapted optotypes for a visual task for a subject who has been corrected for the second principal meridian of his cylindrical refractive error with an optical sphere correction; Fig. 3B, which is for the in Fig. 3A shows the visual impression of a subject whose second principal meridian of cylindrical refractive error is corrected with an optical sphere correction; Fig. 4A the visual impression of a subject of adapted optotypes resulting from differently dimensioned optotypes, wherein the subject is corrected for the second principal meridian of his cylindrical refractive error with an optical sphere correction; Fig. 4B the visual impression of a subject of adapted optotypes resulting from differently dimensioned optotypes, wherein the subject is corrected for the second principal meridian of his cylindrical refractive error with an optical sphere correction; Fig. 5A Examples of adapted optotypes for a visual task for a subject who has been corrected for the second principal meridian of his cylindrical refractive error with an optical sphere correction; Fig. 5B, which is for the in Fig. 5A shows the visual impression of a subject whose cylindrical refractive error is corrected for the second principal meridian with an optical sphere correction; Fig. 6. An exemplary image or photograph that conveys a feeling of distance to the viewer; Fig. 7 the picture or photo of Fig. 6 with exemplary adapted optotypes integrated into or superimposed on the image; and Fig. 8 A diagram showing the range of accommodation as a function of age (Duane curve).

[0088] The figures show embodiments of optotypes and the resulting visual impression in a subject with astigmatic refractive error. The subject is assumed to have a refractive error of +2.75 diopters in the sphere and an astigmatism of -3.0 diopters at an axis of 12°. These refractive error parameters are to be understood as examples, and the following embodiments are generally applicable to subjects with a refractive error of s in the sphere and an astigmatism of z at an axis of α.

[0089] The subject's refractive error can be determined through subjective and / or objective refraction. This yields refractive error data that includes spherical and astigmatic refractive errors, including axis position, i.e., at least the set of values ​​{s; z; α}, in this example the set of values ​​{+2.75dpt; -3.0dpt; 12°}.

[0090] Fig. Figure 1A shows examples of optotypes that can be displayed to the test subject to determine their visual acuity. Landolt rings are used as optotypes, with the gaps oriented from left to right at angles of 180°, 135°, 90°, 45°, and 0°. These five left-hand Landolt rings are standard optotypes, such as those used in conventional visual acuity testing.

[0091] Right in Fig. 1A shows two special and adapted optotypes, where the gap is shown aligned to the angles 168° and 78°.

[0092] When determining visual acuity, the subject is fitted with and / or presented with an optical correction, which allows the subject to view and attempt to identify optotypes. A refraction unit, positioned, for example, in front of the subject's eye(s), can be used for this purpose.

[0093] For example, a refraction unit can be used that can only apply optical sphere corrections to the subject, but not necessarily optical cylinder corrections. Thus, a refraction unit that only corrects spherically can be used, or a refraction unit that can only apply a limited selection of axis positions and / or optical cylinder corrections.

[0094] To determine the visual acuity characteristics of the subject, a preferred direction is first selected from the refractive error data. The preferred direction is a direction in a plane that is approximately perpendicular to the subject's line of sight. The preferred direction can be located in the same plane in which the axis of the subject's cylindrical refractive error is defined.

[0095] The preferred direction can now be either the axis α, and thus the first principal meridian of the subject's cylindrical refractive error, or a perpendicular direction in the same plane, α + 90°, and thus the second principal meridian of the subject's cylindrical refractive error. In the example, the first preferred direction for the first principal meridian would be a direction of 12° in a plane approximately perpendicular to the subject's gaze direction, and the second preferred direction for the second principal meridian would be a direction of 102° in a plane approximately perpendicular to the subject's gaze direction.

[0096] If the first preferred direction is selected, the subject can be given an optical sphere correction of s using the refraction unit, in this example +2.75 diopters. This correctly corrects their refractive error in the first preferred direction, but not in the other directions, especially not perpendicular to the first preferred direction.

[0097] If the second preferred direction is selected, the subject can be given an optical sphere correction of s+z using the refraction unit, in this example -0.25 diopters (calculated from: +2.75 diopters - 3.0 diopters). This correctly corrects their refractive error in the second preferred direction, but not in the other directions, especially not perpendicular to the second preferred direction.

[0098] If, for example, the subject is given an optical sphere correction of -0.25 diopters, their refractive error under the second preferred direction V2 at 102° is corrected relatively accurately. This correction is in Fig. Figure 1B, far left, is shown schematically. Since the axis length of the refractive error is normally determined by looking at the subject's eyes, and the optotypes are usually displayed from the subject's perspective, the measurement angle of the axis position is exactly the mirror image of the display angle of the optotypes. This means that the second preferred direction V2 is aligned at a display angle of 78° on a display showing the optotypes, which corresponds to an axis position at a measurement angle of 102° when looking at the subject's eyes.

[0099] For example, a vertically upward-pointing display angle (corresponding to "12 o'clock") corresponds to the 90° position. Likewise, a vertically upward-pointing measurement angle (corresponding to "12 o'clock") on the display plane also corresponds to 90°.

[0100] A rightward-facing display angle at "3 o'clock" corresponds to 0°. However, this rightward-facing display angle corresponds to a measurement angle rotated to the left (since it is mirrored) when looking at the display plane, i.e., a measurement angle of 180°.

[0101] Therefore, there are differing angle values ​​between the display angles, which are defined on the display plane of the display, and the measurement angles, which are measured with a view to the eyes of the test subject.

[0102] Fig. 1B shows the subject's visual impression when viewing the in Fig. The optotypes shown in Figure 1A appear blurred, particularly in the direction perpendicular to the second preferred direction V2. The optotypes shown in Figure 1A are blurred. Fig. The visual impression shown in 1B is calculated for the subject from the example with the refractive error data {s=+2.75dpt; z=-3.0dpt; α=12°}.

[0103] As in Fig. When shown in 1B, the optotypes in particular, where the gap is shown at the display angles of 90° and 45°, appear very blurry to the test subject.

[0104] For the test subject, specially adapted optotypes are now used, in which the gap is aligned perpendicular to the second preferred direction V2, i.e., at display angles of 168° and 348°. The adapted Landolt ring at display angle 168° is also used above this angle. Fig. 1A is shown as the actually displayed, adjusted optotype. In these two adjusted optotypes, a directional feature of the Landolt ring is aligned exactly parallel to the second preferred direction V2, namely the transition from the black circle's edge to the white gap and back to the black circle's edge. Therefore, at least the gap of the two adjusted Landolt rings, "rotated" to the display angles of 168° and 348°, appears relatively sharp to the test subject; see the two right-hand visual impressions in [reference missing]. Fig. 1B. This is because the subject's refractive error in his second principal meridian, i.e. along the second preferred direction V2, is quite well and / or optimally corrected by the provision of the optical sphere correction of -0.25 diopters.

[0105] The directional feature of the Landolt rings, whose gap is indicated at the display angles of 90° and 45°, is relatively steep (i.e., almost perpendicular) to the corrected second preferred direction V2, which is why a strongly blurred visual impression results, especially for these two optotypes. However, blurred visual impressions also occur for the other standard optotypes, preventing an accurate determination of visual acuity.

[0106] If the subject is fitted with an optical sphere correction of +2.75 diopters, their refractive error under the first preferred direction V1 at a measurement angle of 12° is corrected relatively accurately or optimally. This correction is in Fig. 1C is indicated on the far left. This axis length under the measuring angle of 12° appears on the display in the display plane under the display angle of 168°. Thus, the first preferred direction V1 is aligned on the display under the display angle of 168°.

[0107] Fig. 1C shows the subject's visual impression when viewing the in Fig. The optotypes shown in Figure 1A appear blurred, particularly in the direction perpendicular to the first preferred direction V1. The optotypes shown in Figure 1A are blurred. Fig. The visual impression shown in 1C is again calculated for the subject from the example with the refractive error data {s=+2.75dpt; z=-3.0dpt; α=12°}.

[0108] As in Fig. When shown in 1C, the standard optotypes, in which the gap is shown at the display angles of 180°, 135°, and 0°, appear particularly blurry to the test subject.

[0109] For the test subject, specially adapted optotypes can now be used again, in which the gap is aligned perpendicular to the first preferred direction V1, i.e., at display angles of 258° and 78°. The adapted Landolt ring at display angle 78° is also available above this angle. Fig. 1A is shown as the actually displayed, adjusted optotype. In both adjusted optotypes, the directional feature of the Landolt rings is aligned exactly parallel to the first preferred direction V1, namely the transition from the black circle's edge to the white gap and back to the black circle's edge. Therefore, at least the gap of the two adjusted Landolt rings, rotated to the display angles of 258° and 78°, appears relatively sharp to the test subject; see the two right-hand visual impressions in Fig. 1C. This is again due to the fact that the refractive error of the subject in his first principal meridian, i.e. along the first preferred direction V1, is quite well and / or optimally corrected by the provision of the optical sphere correction of +2.75 diopters.

[0110] The directional feature of the Landolt rings, the gap of which is shown at the display angles of 180°, 135°, and 0°, is relatively steep (i.e., almost perpendicular) to the corrected first preferred direction V1, which is why a strongly blurred visual impression results, especially for these three optotypes.

[0111] As part of a visual task to determine visual acuity, the subject, whose second preferred direction V2 is corrected with an optical sphere correction of -0.25 diopters, can now be asked where the gaps of the two optotypes displayed at angles of 168° and 348° point, e.g., whether they point more to the left or right.

[0112] Alternatively or additionally, the subject, whose first preferred direction V1 is corrected with an optical sphere correction of +2.75 diopters, can be asked in another visual task to determine visual acuity where the gaps of the two optotypes displayed at angles of 258° and 78° point, e.g., whether they point more upwards or downwards.

[0113] This allows testing to determine whether the subject can still recognize the directional feature as a detail of the adjusted optotype. Depending on the level of detail the subject can just barely discern, the visual acuity for the selected preferred direction V1 and / or V2 can be determined.

[0114] For the calculation of the resulting visual impression, which in Fig. 1B and Fig. As shown in Figure 1C and the following figures, it was assumed that the subject's pupil diameter was 3.0 mm, the wavelength was 550 nm, and the distance to the display was 5 m. Furthermore, it was assumed that the optotypes were displayed as a rendered image with 1024×1024 pixels, where the image has a side length of 204.8 mm and the side length of one pixel corresponds to 40 µrad = 0.1375 arcminutes.

[0115] The Snellen-E belongs to the same category of adapted optotypes as the Landolt rings. The relevant feature, i.e., the directional characteristic of the Snellen-E, is the sequence: - dark area of ​​an outer cross line, - bright area of ​​the background, - dark area of ​​the middle cross line, - bright area of ​​the background, and - dark area of ​​the other outer cross line.

[0116] The light background above and / or below may also form part of the sequence. Therefore, when using Snellen Es, the longitudinal line connecting the transverse lines must be oriented parallel to the selected and corrected preferred direction V1 or V2, which, as with the Landolt ring, allows only two different orientations.

[0117] Fig. Figure 2A shows further adapted optotypes for the subject with the exemplary refractive error. The adapted optotypes are hatched, borderless squares with solid lines, which are displayed on the screen. The hatching lines of the first, third, and fourth optotypes from the left are aligned parallel to a display angle of 78°, while the hatching lines of the second optotype from the left are aligned parallel to a display angle of 168°.

[0118] The hatching lines of each optotype all have the same thickness and orientation. Any two adjacent hatching lines always maintain the same and constant distance from each other.

[0119] The hatching lines provide a directional feature of the adapted visual acuity symbols. The direction of this directional feature is the direction of the change between light and dark areas, i.e., the direction perpendicular to the hatching lines.

[0120] If the subject is corrected by applying a purely spherical optical correction of -0.25 diopters for their second preferred direction V2, then the subject will have the following result: Fig. Visual impression shown in 2B. The first, third and fourth optotypes from the left appear as grey spots, while the hatching of the second optotype can be recognized by the subject.

[0121] The subject can thus, within the context of a visual acuity task, identify the adapted optotype that differs from the others. In this example, it is the second optotype from the left, whose directional feature is aligned parallel to the selected and corrected second preferred direction V2, i.e., the display angle of 78° corresponds to the measurement angle of 102°, which is the second principal meridian of the subject's cylindrical refractive error.

[0122] The distance between two adjacent hatching lines and / or the thickness of the black hatching lines can be used to determine the visual acuity of the detected detail.

[0123] Fig. Figure 3A shows further optotypes for the test subject with the exemplary refractive error. The optotypes are again hatched, borderless squares with solid lines, which are displayed on the screen. Here, the hatching lines of the first, third, and fourth optotypes from the left are aligned parallel to a display angle of 315°, while the hatching lines of the second optotype from the left are aligned parallel to a display angle of 135°.

[0124] The size of the squares, as well as the spacing and thickness of the hatching lines, can be adjusted accordingly. Fig. The optotypes shown in 2A correspond to the optotypes. Again, the second optotype from the left differs from the others.

[0125] If the subject is corrected by applying a purely spherical optical correction of -0.25 diopters for their second preferred direction V2, then the subject will have the following result: Fig. 3B shows the visual impression. Since none of the optotypes are well adapted to the corrected second preferred direction V2 under the display angle of 78°, the subject cannot recognize a single hatching of the optotypes, because for him the visual impression of a grey spot or blurred square results for each of the four optotypes.

[0126] The visual impression thus differs significantly from the visual impression obtained with optotypes optimized for the subject, cf. Fig. 2A and Fig. 2B.

[0127] Fig. Figure 4A shows the subject's visual impression when corrected by applying a purely spherical optical correction of -0.25 diopters for their second preferred direction V2 at a display angle of 78°. Four borderless hatched squares are displayed as optotypes, with their hatching lines parallel to a display angle of 168°. This aligns the directional feature of these optotypes parallel to the corrected second preferred direction V2, allowing the subject to distinguish at least the hatching of some of the adjusted optotypes, e.g., the two rightmost adjusted optotypes.

[0128] The hatched lines of the optotypes, however, have different widths and spacings. The leftmost optotype has a distance between two black hatched lines of logMAR -0.66, the second optotype from the left of -0.26, the third optotype from the left of 0.14, and the fourth optotype from the left of 0.54. This distance can be used as a measure of visual acuity. Therefore, if the subject can only recognize the two optotypes on the right, of which the more finely hatched optotype (i.e., the third from the left) has a distance of logMAR 0.14, this smallest discernible detail can be used to determine visual acuity.

[0129] Fig. Figure 4B shows the subject's visual impression when corrected by applying a purely spherical optical correction of -0.25 diopters for their second preferred direction V2 at a display angle of 78°. Here again, four borderless hatched squares are displayed as optotypes, their hatching lines as in Fig. 4A have different widths and different spacings. From left to right, the optotypes point in the same way as in Fig. 4A a distance between two adjacent black hatching lines of logMAR-0.66; -0.26; 0.14 and 0.54.

[0130] The hatching lines are displayed parallel to the display angle of 78°, which is why they appear maximally blurry to the test subject; this is because the directional features of the optotypes are aligned perpendicular to the corrected second preferred direction V2. Thus, the in Fig. The optotypes used in 4B can at most be used as grey-appearing optotypes, but not as adapted optotypes recognizable to the subject thus corrected.

[0131] Fig. Figure 5A shows further optotypes for the test subject with the exemplary refractive error. The optotypes are hatched, borderless squares with continuous lines, displayed on the screen. The hatching lines of all optotypes are aligned parallel to a display angle of 168°. However, only half of the squares are hatched. For the first and third optotypes from the left, the upper halves are hatched; for the second and fourth optotypes from the left, the lower halves are hatched. The other halves are filled in gray for the first and second optotypes from the left, and with a shortened hatching perpendicular to the gray lines (i.e., parallel to a display angle of 78°) for the third and fourth optotypes from the left.

[0132] The hatching lines provide a directional feature of the adapted visual acuity symbols. The direction of this directional feature is the direction of the change between light and dark areas, i.e., the direction perpendicular to the hatching lines.

[0133] If the subject is corrected by applying a purely spherical optical correction of -0.25 diopters for their second preferred direction V2, then the subject will have the following result: Fig. Visual impression shown in 5B. For the first and third optotypes from the left, the hatching appears in the upper half, for the other two in the lower half.

[0134] The other half of each optotype appears as a grey patch. For the test subject, it makes little difference whether the other half is actually filled with a medium grey value or with hatching lines parallel to the selected second preferred direction.

[0135] The subject can therefore be asked, as part of a visual task to determine visual acuity, to distinguish the displayed adapted optotypes depending on their visual acuity.

[0136] This also allows the use of optotypes that have differently filled areas, in particular hatching that only fills part of the adapted optotype.

[0137] The size of the recognized detail for determining visual acuity can again be determined by the distance between two adjacent hatching lines and / or the thickness of the black hatching lines.

[0138] As an alternative to the hatched squares shown in the figures, any type of shape, such as circles, rectangles, symbols, animals, letters, etc., filled with hatching, can be used as adapted visual acuity symbols. Preferably, they should not have any border lines that could affect the visual perception of the hatching.

[0139] The hatching lines can be perpendicular to the selected and corrected preferred direction V1 or V2, since the directional feature and relevant characteristic is the alternation of light and dark areas within the hatching lines. For this method, it is advantageous if the figure itself has as few details as possible, such as a circle or a square. To adjust the orientation, the entire optotype, including the hatching, or only the hatching within the optotype can be rotated. The hatching can be binary, i.e., with hard black edges, or continuous, e.g., with a sinusoidal intensity gradient. Visual tasks

[0140] To determine visual acuity, subjects can be given visual tasks in which adapted optotypes are displayed. These visual tasks can be categorized as either those with active or passive feedback from the subject. Active feedback can be understood as a statement from the subject, either verbally or by consciously viewing an optotype and recording their gaze direction using eye tracking. Passive feedback can be understood as following a moving optotype. The eye movement recorded by an eye-tracking unit allows conclusions to be drawn as to whether the optotype is still being reliably recognized.

[0141] The optotypes are displayed and thus presented to the test subject using a defined presentation method. A presentation method encompasses properties such as contrast, size, and hatching frequency. Size is a particularly important property for optotypes that can be displayed in two ways that are mirror images of each other with respect to the selected preferred direction, such as Landolt rings and Snellen Es. Hatching frequency is a particularly important property for optotypes that feature hatched areas and / or consist of hatched areas.

[0142] The presentation may be worsened by changing the presentation style to one that makes it less recognizable, for example by reducing the size (especially in the case of adapted optotypes of the type that can be displayed in two ways that are mirror images of the selected preferred direction), reducing the contrast and / or increasing the frequency of the hatching (especially in the case of adapted optotypes of the type that have hatched areas and / or consist of hatched areas).

[0143] In one embodiment of a visual task with active feedback, one or more adapted optotypes are presented, which can be displayed in two ways that are mirror images of the selected preferred direction. The subject is expected to recognize the orientation of these displayed optotypes.

[0144] Displaying several optotypes of the same presentation allows for a more reliable assessment of the response. Deteriorating the presentation style until the optotypes can no longer be recognized allows for the determination of visual acuity.

[0145] In one embodiment of a visual task with active feedback, one or more adapted optotypes are presented that have hatched areas and / or consist of hatched areas. The subject is asked to identify the presence of hatching in the optotype.

[0146] Displaying several optotypes of the same presentation allows for a more reliable assessment of the response. Deteriorating the presentation until the optotypes or the presence of hatching can no longer be recognized allows for the determination of visual acuity.

[0147] Furthermore, one or more adapted optotypes with adapted orientations, as well as one or more adapted optotypes with a different orientation (e.g., orthogonal orientation), can be presented. For optotypes that have hatched areas and / or consist of hatched areas, the optotypes can be presented with uniform fill, and the subject can be asked whether they can discern differences and / or which one or more optotypes differ from the others. This type of visual task is also known as a "forced choice" task.

[0148] In one embodiment of a visual task with passive feedback, one or more adapted optotypes of one of the aforementioned types are presented in motion. The presentation method can be continuously and / or gradually degraded. Based on the eye movements recorded by an eye-tracking unit, it is then possible to determine the presentation conditions under which the optotype and / or visual object is still reliably recognized. From this, the subject's visual acuity can be derived and / or determined.

[0149] The optotypes can be displayed using a light field display. The applied optical sphere corrections do not need to be physically applied; instead, they can be simulated as wavefronts. Combination with eye tracking

[0150] For visual tasks with active feedback, eye tracking allows for automation of the process; for visual tasks with passive feedback, eye tracking may be absolutely necessary.

[0151] In one embodiment, the subject's gaze direction while performing the visual task can be determined using at least one image and / or video of the pupil and / or one or more Purkinje reflexes. The gaze direction can also be determined from a combination of methods, e.g., using Purkinje reflexes captured in a video of the pupil. For this purpose, the device for determining visual acuity can include at least one calibrated image capture device, e.g., a digital camera.

[0152] In one embodiment, an eye-tracking unit is used to position an optical unit, i.e., to center and / or focus the optical unit. For example, a measuring head of the device can be centered and / or focused. This positioning can then be kept constant, and the eye-tracking unit can be used to determine the subject's gaze direction, for example, for passive and / or active response to a visual task. In this way, different tasks can be performed with just a single eye-tracking unit. Integration into an optometric measuring device

[0153] Visual acuity testing can be combined with refractive error testing, particularly to determine refractive errors in terms of sphere, cylinder, and axis. This also allows for the determination of lower-order and, if applicable, higher-order aberrations.

[0154] For this purpose, a device for determining visual acuity is connected and / or combined with an autorefraction or aberrometry unit.

[0155] In one embodiment, an autorefractor and / or an aberrometer is used as the refraction unit, which includes a display unit and an optical unit used to display the adjusted optotype and thus the target. This unit can optionally also be used for fogging to determine visual acuity without requiring additional optical components.

[0156] Ideally, the display unit is designed as a programmable display to show customized representations for different tasks. Alternatively, the optotype display can be used with fog for autorefractometric and / or aberrometric measurements. Switching between the displays is possible using a beam splitter and / or mechanical means.

[0157] Such a device makes it possible to first determine the refractive error using the autorefractometer and / or the aberrometer, and to derive the refractive error data and the preferred direction with the effect to be applied to this preferred direction from the result of this measurement.

[0158] With such a device, an existing eye-tracking unit, which is used to center and / or focus the autorefractometric and / or aberrometric measurement, can be used for eye-tracking the gaze direction of the subject.

[0159] The same unit can be used in this device to present at least one optotype, and thus the target, and optionally a fog, during autorefractometric and / or aberrometric measurements. For autorefractometric and / or aberrometric measurements, using a relatively small optotype as a target can be sufficient or even advantageous, as it pre-adjusts the subject's gaze before fine-tuning is achieved by looking at a prominent optotype.

[0160] In a foggy state, a small optotype can be used as a target and / or be advantageous because - provided the subject cannot see details - the small bright spot of a small target controls the gaze better than a more extensive one.

[0161] For visual acuity testing, a larger optotype target is often helpful, as it allows for the presentation of several different optotypes and, particularly in visual tasks where eye movement is recorded, permits a greater degree of eye movement. This can be achieved with a component device that allows adjustment of both the vergence and / or divergence (the "optical distance") of the light from the presented target and the size of the target image. This can be accomplished, for example, by combining a display with two axially movable spherical lenses, where the axial distances of both lenses can be adjusted independently of the display.

[0162] One or more other measurement units can be integrated additionally or instead, such as an opacity unit, a topography and / or tomometry unit, a Scheimpflug camera, and / or a tonometry unit. Individual components from multiple units can also be used. Influence of accommodation and other principal meridian

[0163] Should the precise design of the optotypes and / or the visual task potentially lead to an influence of accommodation and / or the unconsidered principal meridian, the procedure can be varied as follows.

[0164] Accommodation causes the planes in which both principal meridians are sharply focused to be shifted forward (i.e., from the retina towards the lens). Therefore, in this embodiment, the posterior principal meridian (i.e., the one refracted less sharply by the eye) is sharply focused on the retina with spherical correction, and / or, if blurring (e.g., during sensitivity testing) is desired, it is projected in front of the retina. To avoid the influence of accommodation, the preferred direction for presenting the optotypes is the direction in which the less sharply refracted principal meridian is sharply focused.

[0165] According to one embodiment, the preferred direction is thus the principal meridian for which the subject's eye exhibits weaker refraction. This reduces the effect of accommodation on visual acuity measurement.

[0166] In order to avoid the influence of the other principal meridian when determining visual acuity for an optical sphere correction that deviates from the best correction in the principal meridian under consideration, e.g., in the case of an applied blur, e.g., to determine sensitivity, the correction can deviate against the direction that would be required for the correction in the other principal meridian.

[0167] In this context, particularly with regard to the preceding consideration of accommodation, a consideration of the less refracting principal section and a blurring in the positive direction is used, which is also referred to as nebulization in the narrower sense.

[0168] Thus, in one embodiment, the principal meridian for which the subject's eye exhibits weaker refraction is selected as the preferred direction. To determine sensitivity, a visual acuity value is recorded using an optical sphere correction that deviates positively from the determined optimal optical sphere correction. Additionally, a visual acuity value can be recorded using the determined optimal optical sphere correction. From these two visual acuity values, both the subject's visual acuity and sensitivity can be determined as accurately as possible, thereby reducing the influence of both accommodation and the other principal meridian. Consideration of HOA

[0169] If a wavefront measurement of the eye is performed, possibly also taking into account higher-order aberrations (HOA), this wavefront measurement can be used instead of the objectively and / or subjectively determined refraction values ​​to provide the refractive error data. Thus, the preferred direction can be selected based on the wavefront measurement, which then serves as the basis for the adjusted optotypes. Furthermore, the strength of the optical sphere correction required for this selected preferred direction can also be derived from the wavefront measurement.

[0170] A point spread function can be determined from the wavefront data, the optical sphere correction (and / or corrections) applied during visual acuity testing, and a pupil size, using methods known from the literature. Instead of determining the preferred direction of the adjusted optotypes based on the subjective and / or objective refraction in second (Zernike) order, the preferred direction can be derived from the point spread function, e.g., from the direction and / or axis of the smallest extent of the point spread function. Here, the direction of least confusion can be selected, e.g., as the direction of the smallest standard deviation of the point spread function. Determination of sensitivity

[0171] In some embodiments, the sensitivity of at least one eye of a test subject or spectacle wearer is determined. This allows for the calculation, optimization, or evaluation of a spectacle lens for the test subject's at least one eye, taking into account the determined sensitivity of that eye. This can be used in the manufacturing of spectacle lenses.

[0172] In state-of-the-art methods for optimizing a spectacle lens, the lens is optimized by minimizing or maximizing an objective function that incorporates actual values ​​and corresponding target values ​​of at least one imaging property or aberration of the lens. This at least one imaging property or aberration can directly quantify a wavefront deviation from a reference wavefront. An example objective function is, for instance: F=∑i[GR,i(RIact(i)−RSoll(i))2+GA,i(AIst(i)−ASPK,Somm(i))2+...], where: i (i = 1 to N) denotes an evaluation point of the spectacle lens; R Ist (i) denotes the actual spherical effect or refractive error at the i-th evaluation point; R Ist (i) denotes the spherical target effect or the target refractive error at the i-th evaluation point; Branch Ist (i) denotes astigmatism or astigmatic error at the i-th evaluation point; Branch soll (i) denotes the target astigmatism or the target astigmatic error at the i-th evaluation point.

[0173] Sizes G R,i ,G A,i ,... are weights of the respective mapping property or aberration that are used in the optimization.

[0174] A direct quantification of wavefront deviation in diopters without considering the effective pupil size is not the best possible criterion for describing and evaluating a spectacle wearer's perception through a lens, due to the dependent depth of field. Based on this finding, DE 10 2017 007 663 A1 proposes that the target or...

[0175] The quality function directly considers visual acuity. The visual acuity included in the target or quality function depends on the assignment of at least one imaging property or aberration of a spectacle lens system, whereby the at least one imaging property or aberration can be evaluated at a suitable evaluation surface (e.g., at the vertex sphere or in the eye). The spectacle lens system can consist of at least one lens (e.g., a lens from a refraction spectacle). Preferably, however, the spectacle lens system includes further components such as a model eye or eye model, which can be based on average values ​​of spectacle wearers or on at least one individual parameter of the spectacle wearer's eye. In other words, the spectacle lens system underlying the assignment of at least one imaging property or aberration to the spectacle wearer's visual acuity can be a spectacle lens-eye system.

[0176] As described in DE 10 2017 007 663 A1, an exemplary objective or quality function, which is derived from the visual acuity V via the assignment of at least one imaging property or aberration ΔU, can be used. s,j depends on the visual acuity of the spectacle wearer or an average spectacle wearer, e.g. exhibiting the following structure: Fs=∑i[Gs,j,iV(VIact(ΔUs,j(i))−Vset(ΔUs,j(i)))2+...].

[0177] In the formula above, V(ΔU) denotes s,j (i)) a function that describes the dependence of visual acuity on at least one imaging property or aberration of a spectacle lens system at the i-th evaluation site (i = 1, 2, 3, ..., N) on an evaluation surface. In other words, V(ΔU) describes s,j(i)) an exemplary assignment of at least one imaging property or aberration of a spectacle lens system to the visual acuity of the subject or spectacle wearer or of an average spectacle wearer when viewing an object through the spectacle lens system. The argument ΔU s,j is generic and can denote any imaging property or aberration of a spectacle lens system, describing the effect of the spectacle lens system on a light beam emanating from an object or the difference between the effects of the spectacle lens system on a light beam emanating from an object and on a reference light beam converging on the retina of the eye. One or more imaging properties or aberrations can be included in and evaluated in the objective or quality function, where the subscript j,j ≥ 1 denotes the j-th imaging property or aberration.

[0178] V Ist (ΔU s,j(i)) refers to the visual acuity determined at the i-th evaluation point based on the assignment and actual value of at least one imaging property of the spectacle lens to be calculated (e.g. optimized) or evaluated, and V Soll (ΔU s,j (i)) denotes the corresponding target value for visual acuity.

[0179] At least one imaging property or aberration can be calculated or evaluated on a suitable evaluation surface. The subscript "s" accordingly stands for any evaluation surface for the at least one imaging property or aberration 4U. s,j The evaluation surface can be, for example, a plane (evaluation plane) or a curved (e.g., spherical) surface. The evaluation surface can be, for example, the vertex sphere or a surface within the eye, such as one of the following planes or surfaces: a plane or a (e.g. spherical) surface behind the cornea, the anterior surface of the eye lens or a plane tangential to the anterior surface of the eye lens, the posterior surface of the eye lens or a plane tangential to the posterior surface of the eye lens, the level of the exit pupil (AP); or the plane of the lens posterior surface (L2).

[0180] The size Gs,iso,iV denotes the weighting of the function assigned to the mapping property ΔU s,j specified visual acuity at the i-th evaluation point.

[0181] For example, one of the visual acuity models described in DE 10 2017 007 663 A1, or any other suitable visual acuity model (which in particular describes visual acuity as a function of refraction or refraction error), can be used, preferably in combination with a procedure for how the visual acuity model, in conjunction with a transformation of the target values ​​and weights, is to be incorporated into the objective function of an optimization. It should be noted here that, within the scope of this description, a sensitivity metric (as described below) can preferably be used based on such a visual acuity model (as a functional dependence of a visual acuity value on refraction / refraction error). In particular, a preferred sensitivity metric could be used as a derivation of a visual acuity model (i.e., the function of the visual acuity value on refraction / refraction error) with respect to refraction / refraction error.

[0182] The objective function can also be used to evaluate a spectacle lens, whereby the actual value of at least one imaging property of the spectacle lens to be evaluated is calculated at at least one evaluation point of the spectacle lens to be evaluated and compared with the corresponding target value.

[0183] As further explained in DE 10 2017 007 663 A1, knowledge of the so-called sensitivity, i.e., the change in visual acuity with refractive error, is particularly helpful for calculating, optimizing, and / or manufacturing highly individualized and high-quality spectacle lenses. Thus, the assignment of at least one imaging property or aberration of a spectacle lens system to the visual acuity of the spectacle wearer, or the function V(ΔU), can be used. s,j(i) ) depend parametrically on the measured initial visual acuity and / or the determined sensitivity of the spectacle wearer.

[0184] Sensitivity is a quantity or parameter used in spectacle optics and ophthalmology (especially phenomenologically) to describe or specify the dependence of visual acuity on refractive error. The sensitivity of an eye refers specifically to the change in visual acuity in response to a change in refractive error. In particular, sensitivity can be defined as the derivative of visual acuity after refractive error, or as the local derivative of visual acuity after refractive error for a specific refractive error. Refractive error is a deviation of the effect or refraction applied to at least one eye of the subject during visual acuity testing from an ideal refraction determined or known for that eye. The ideal refraction (hereinafter also referred to as optimal refraction or target refraction) can, for example, be...Sensitivity can be determined from a conventional objective and / or subjective refraction measurement. In particular, it describes how much visual acuity changes when an optical effect or correction placed in front of the eye is altered. Sensitivity can be quantitatively described, especially using a sensitivity metric and / or a visual acuity model.

[0185] The sensitivity of at least one eye of a test subject can thus be taken into account when calculating and / or creating individual spectacle lenses, especially when creating multifocal lenses such as ophthalmic lenses. Spectacle lenses can have transitions between areas with different optical corrections, for example, transitions between a viewing point for distance and a viewing point for near vision. These transitions between lens areas with different optical corrections can be designed in various ways. For example, they are referred to as hard or soft transitions, depending on how sharp or gradual the change in refraction is along the transition. In highly individualized and high-quality spectacle lenses, such a transition (but also other areas of the lens) can specifically influence the sensitivity of at least one eye of the test subject.be adjusted for eyeglass wearers.

[0186] To determine the sensitivity of at least one eye of a subject to blur, at least two applied effects and the corresponding visual acuity achieved with each are required. Within the scope of the invention, these can be determined as visual acuity-refraction value pairs of the visual acuity characteristics. Relevant models and corresponding formulas for calculating sensitivity are described below. According to the prior art, to determine sensitivity, quantized effects are presented to the subject or at least one eye of the subject (e.g., in steps of 0.25 diopters using conventional trial lenses). Using a visual acuity chart with optotypes in quantized sizes or quantized visual acuity levels, the corresponding visual acuity is determined for each presented effect. Furthermore, the optimal correction (or the optimal refraction) must be determined for the subject.Target refraction) must be determined in order to convert the expected effects into a false refraction.

[0187] The double quantization inherent in the conventional method leads to high measurement uncertainty. Conventional methods are not only time-consuming but can also be psychologically disadvantageous, since at least one of the subject's eyes is given a weaker correction after the optimal refraction has been determined, and the subject then has to perform visual tasks with this weaker correction to determine sensitivity. This sequence is necessary in the conventional approach because a defined fogging for visual acuity measurement can only be set once the optimal refraction is known.

[0188] According to one aspect, it is therefore an object of the present invention to determine the sensitivity of at least one eye of the test subject, which is particularly necessary for calculating, optimizing, evaluating, and / or manufacturing highly individualized and high-quality spectacle lenses, in an improved manner, especially in a simple and rapid way. Furthermore, it may be an object of the present invention to provide a method and a device for calculating, optimizing, evaluating, and manufacturing spectacle lenses that are highly individualized and of high quality due to the consideration of the sensitivity of at least one eye of the test subject. It may also be an object of the present invention to provide such improved spectacle lenses. Determination of sensitivity as a visual acuity characteristic under variation of the applied optical effect

[0189] In some embodiments, the sensitivity of at least one eye of a subject is determined as a visual acuity characteristic based on at least two provided visual acuity-refraction value pairs.

[0190] While in one alternative the applied optical effect is kept constant and changed, in a second alternative the dimension of the directional feature of the adapted optotype is kept constant and the applied optical effect is varied. This second alternative is explained in more detail below.

[0191] In this second alternative, the visual acuity-refraction value pairs can be provided through the following steps: - Projecting a target, which may contain at least one adapted optotype, with an adjustable target refraction corresponding to the applied optical effect, into at least one eye of the subject, wherein the target is designed to verify a predetermined visual acuity; and - Determining a visual acuity limit refraction of at least one eye of the subject corresponding to the given visual acuity by varying the target refraction of the target projected into at least one eye of the subject and recording a subject action which establishes that the identifiability of the target for the subject has changed at the time of the subject action.

[0192] As mentioned at the beginning, the "sensitivity" (with regard to blurriness) of at least one eye of the subject is understood as the dependence of the visual acuity of at least one eye of the subject on a refractive error, whereby the "refractive error" is a deviation of an effect or refraction applied to at least one eye of the subject during the visual acuity determination from an ideal or optimal refraction (target refraction) determined or known for at least one eye.

[0193] Visual acuity (or "visual acuity") is a measure of the (central) sharpness of at least one eye of a subject. Visual acuity is usually determined in bright light. Specifically, it can be defined as the reciprocal of the smallest perceptible gap in the standard optotype, the Landolt ring. In humans, visual acuity can be determined using a vision test. Optotypes are presented to the subject, and their responses indicate whether they have correctly identified them. Visual acuity depends on which optotypes the subject can identify with the correct refraction. Optotypes typically have a defined size, brightness, shape, and contrast. They can be displayed on a chart or projected.

[0194] In the method according to the invention, the target comprises at least one adapted optotype for each visual task, in which the directed feature is arranged parallel to the selected preferred direction.

[0195] Using a projector instead of a chart has the advantage of being independent of the testing distance. DIN standards exist for reproducible visual acuity testing. According to these standards, the standard optotype is the so-called Landolt ring, a ring of defined width with a gap of the same width, which can be positioned in eight different directions. By recognizing the direction of the gap, the test subject demonstrates that their resolving power is at least equal to the width of the gap. In practice, however, standardized images of numbers are usually used as optotypes because they are easier to understand. Other standardized optotypes also exist, such as the "Snellen E," the "Pflüger E-hook" (in which the middle line is shorter), and others suitable for testing the visual acuity of illiterate individuals and preschool children, as well as for non-verbal communication.

[0196] Visual acuity is determined between corrected vision, such as with glasses or contact lenses, and uncorrected vision. Uncorrected visual acuity is also referred to as raw visual acuity. The abbreviations "sc" ("sine correctione," Latin for "without correction") and "cc" ("cum correctione," Latin for "with correction") are also frequently used.

[0197] The sensitivity of at least one eye can be determined, in particular, based on a sensitivity metric. Using a sensitivity metric, sensitivity can be calculated even if the applied refractive values ​​do not have a predetermined interval between them.

[0198] The sensitivity metric represents the dependence of visual acuity on (mis)fraction. The difference between two refractive values ​​can be part of a sensitivity metric. The sensitivity metric can be defined in the metric space of refractive values. Each refractive value in the sensitivity metric can be assigned a visual acuity value, or vice versa. Refraction can, for example, be defined in at least three-dimensional space. A refractive value can typically be described by the coordinates s, c, and α. Here, s can depend on the strength of an optical correction of the sphere, c on the strength of an optical correction for a cylinder, and α on the axial position of this cylinder. The strength of the optical correction for the cylinder is sometimes denoted by z as an alternative to c.In this metric space of refractive values, at least the refractive values ​​for a given first and a given second visual acuity can be determined and are therefore known when calculating sensitivity. The sensitivity metric can be used to determine the sensitivity as a function of any two fundamentally different refractive values. By using such a sensitivity metric, the determination of sensitivity becomes independent of visual acuity measurements at given refractive values, as is usual with conventional methods. In this way, the determination of sensitivity can become independent of visual acuity measurements at at least one predetermined and / or fixed refractive difference from the refractive result (or from the optimal refraction).Target refraction), and on the other hand, visual acuity measurements at at least one predetermined and / or fixed relative refraction distance between the two applied refractions. This makes it easier for both the refractionist and the subject to obtain the measurement data necessary for sensitivity determination. Examples of a sensitivity metric

[0199] Sensitivity can be calculated using a metric space in which different refractive values ​​represent individual points. A refractive value can be represented three-dimensionally, for example, with the coordinates s, c, and α. Here, s can depend on the strength of a spherical correction and be expressed, for example, in diopters (which can also be abbreviated as dpt). c can depend on the strength of a cylindrical correction and be expressed, for example, in dpt. α can depend on the axis of the cylindrical correction and be expressed, for example, in degrees, e.g., from 0 to 180°. Alternatively, other coordinates can be used.

[0200] In the following example, it is assumed that the best refraction (also referred to as optimal or ideal refraction within this description), i.e., a specific objective and subjective refraction result, is denoted by s0, c0, and α0 in this sensitivity metric, and the corresponding visual acuity is denoted by v0. At least two visual acuity-refraction value pairs are provided when performing the procedure. In general, n refractions can be performed. i , c i , α i with corresponding visual acuity v i with i ∈ [1, ..., n] and n ≥ 2. At least one visual acuity-refraction value pair for at least one eye of the subject may already be known and provided as a known value pair. Providing the values ​​includes, in particular, determining and / or measuring them.

[0201] In one possible sensitivity metric, the difference between a refraction i and the best refraction in the middle sphere d is calculated. i and in the cylinder a i with equation (1) to: di=(si+12⋅ci)−(s0+12⋅c0)ai=ci2+c02−2⋅ci⋅c0⋅cos(αi−α0) Simple bilinear model of a sensitivity metric with knowledge of a target refraction

[0202] In one embodiment of a bilinear model of a sensitivity metric, the following relationship, shown in equation (2), applies to the dependence of visual acuity for each individual measurement for a refraction i. In a simplified case, it can be assumed that the subject cannot compensate for nebulization by accommodation. lgvi=md⋅|di|+ma⋅ai+lgv0

[0203] Here m d for the sensitivity at a spherical distance and m afor the sensitivity at a cylindrical distance. Such a distinction between spherical and cylindrical refractive errors can be used to account for the fact that subjects can react very differently to these two components of a refractive error. Thus, data from D. Methling: Determination of Visual Aids, 2nd ed. Ferdinand Enke Verlag, Stuttgart 1996, show that, empirically determined in the population average, equations (3) approximately apply: md=21dpt⋅lg0.5=−0.601dpt−1ma=11dpt⋅lg0.5=−0.301dpt−1

[0204] In general, the preceding equation (2) has the independent parameters m a , m d , v0. Therefore, the system of equations (2) with three measurements i=1,2,3 of refractions (s1, c1, α1; s2, c2, α2; s3, c3, α3) at three (especially given) different visual acuity values ​​v1, v2, v3 can be uniquely solved for the system of equations (2a): ma=−1denominator(log(v1|d2|−|d3|)+log(v2|d3|−|d1|)+log(v3|d1|−|d2|)) md=−1denominator(log(v1a3−a2)+log(v2a1−a3)+log(v3a2−a1)) log v0=−1denominator(log(v1a2|d3|−a3|d2|)+log(v2a3|d1|−a1|d3|)+log(v3a1|d2|−a2|d1|))with denominator=(a2−a3)|d1|+(a3−a1)|d2|+(a1−a2)|d3|

[0205] For example, a visual acuity measurement can be taken under optimal correction conditions, i.e., at the target refraction (in particular, determined from an objective and / or subjective refraction measurement). Then, for example, at i=3: (s3, c3, α3) = (s0, c0, α0). Under these optimal correction conditions, a3 = a0 = 0 and d3 = d0 = 0. Thus, the third of equations (2a) is automatically satisfied. The other equations then take the following form of the system of equations (4): ma=−1denominator(|d2|log(v1 / v0)−|d1|log(v2 / v0)) md=−1denominator(−a2 log(v1 / v0)+a1 log(v2 / v0))with denominator=a2|d1|−a1|d2|

[0206] The system of equations (4) thus provides an embodiment of a simplified bilinear model of a sensitivity metric. The system of equations (4) can be solved given the target refraction and two additional refraction values ​​for two additional visual acuity values ​​(for i=1,2). The visual acuity-refraction value pairs used here can be determined using the method according to the invention. The sensitivity can then be determined from the system of equations (4). The sensitivity describes the dependence of visual acuity on the (incorrect) refraction. This can be expressed, for example, by the values ​​m a and m d be described.

[0207] If, in addition to the visual acuity v0, more than two additional refractions are measured at given visual acuity values ​​during the target refraction, the sensitivity can be determined more accurately by... d and m dThe sensitivity can be determined from all data using a adjustment procedure, such as the method of least squares. Furthermore, outliers in the measurement data can be excluded to improve the quality of the sensitivity determination. Simplified linear model of a sensitivity metric with knowledge of a target refraction

[0208] In a further simplified, less individualized model of the sensitivity metric, e.g., if only one measurement is available for a refraction error i=1, a relationship between the spherical and cylindrical refraction distances can be assumed according to equation (5): md=mma=f⋅md=f⋅m

[0209] Here, the parameter f can be derived from empirical values ​​and, for example, be a scalar. With the assumption according to equation (5), the system of equations (2) simplifies to the following equation (6): lg vi=m⋅(d1+f⋅a1)+lg v0 lg vi=m⋅(ai+f⋅di)+lg v0

[0210] This allows the sensitivity m to be determined from a measurement with an incorrect refraction i using equation (7): m=ai+f⋅|di|lg vi− lg v0

[0211] A value for f can be derived from relevant literature, e.g., f = 1 / 2, derived from Applegate, RA, Sarver, EJ, Khemsara: “Are all aberrations equal?”, J Refract Surg. 2002, 18: pages 556-562. Or f = 1, derived from Atchison et al.: “Blur limits for defocus, astigmatism and trefoil”, VisionResearch, 2009.

[0212] Equation (5) does not necessarily require a linear relationship. Alternatively, more complex relationships can be formulated, and the sensitivity derived from them—e.g., as a function of the number of independent parameters and / or refraction measurements—by substitution into appropriately resolved equations (see equations (4) and (7)). The sensitivity can also be derived from a least-squares adjustment method. Further models of a sensitivity metric with knowledge of subjective refraction

[0213] Sensitivity can also be calculated based on a different model. For example, R. Blendowske, "Unaided Visual Acuity and Blur: 'A Simple Model'", Optometry and Vision Science, Vol. 92, No. 6, 2015, describes models that are particularly simple and based on only a few parameters. Such simple models are especially suitable for calculating sensitivity and for fitting when data is limited, for example, because they effectively prevent overfitting.

[0214] If a larger number of parameters are individually available, a model with many different parameters is more suitable, as described, for example, in the publication DE 10 2017 007 663 A1.

[0215] In principle, a variety of different models can be used. The specific model used in each case may depend on the number of visual acuity-refraction value pairs provided or determined. With a sufficiently large number of visual acuity-refraction value pairs, relatively complex, not necessarily linear models can be developed, the parameters of which can be adapted to the measurements.

[0216] The models listed above as examples can be generalized, for example, by defining a function describing visual acuity in the power vector space with contours of constant visual acuity that correspond to ellipsoids or ovoids containing the point of maximum visual acuity. This can be done analogously to a method presented in A. Rubin and W.F. Harris: “Closed Surfaces of Constant Visual Acuity in Symmetric Dioptric Power Space”, Optometry and Vision Science, Vol. 78, No. 10, 2001. Axis ratios can vary individually within a range of 0.25 to 4. Instead of individually measured values, mean values, medians, or other estimates of the corresponding model parameters of the population can also be used to calculate visual acuity.

[0217] In one embodiment, a generalization of the preceding equation (6) leads to different factors f, e.g. to equation (8): lg vi={(d1,aiort,aiobl)R[m12000m22000m32]RT(di,aiort,aiobl)T}1 / 2+lg v0

[0218] Here, a denotes i ort and a i ort The astigmatism of refractive error with orthogonal (J0) or oblique (J45) axis positions and are defined as: aiort=−ci2cos(2αi)+c02cos(2α0) and aiobl=−ci2sin(2αi)+c02sin(2α0).

[0219] R represents a rotation matrix, which defines the orientation of an ellipsoid of constant visual acuity in the power vector space of vectors. (di,aiort,aiobl) The eigenvalues ​​m1, m2, m3 denote the sensitivities to nebulization in the direction of the first, second and third column vectors of the rotation matrix R in the power vector space. Implementations of models of a sensitivity metric without knowledge of the target refraction

[0220] In some embodiments, sensitivity can be determined without knowing or determining the target refraction. This is possible if a corresponding refraction or visual acuity limit refraction is determined for several predefined, different visual acuity values. In this case, the best refraction or target refraction can be determined from the resulting measurement data. Furthermore, the actually determined best refraction can be verified from the measurement data using a model of a sensitivity metric.

[0221] It can be assumed that a nebulization, i.e., an intentional refraction error towards minus, can be compensated for by the subject through accommodation of at least one eye. In this case, a point at which the visual acuity curve bends can be chosen in the linear model according to the preceding equations (2) and (6). In non-linear models, where saturation occurs, the optimal refraction can be calculated directly as a parameter of the system of equations. For this purpose, the refraction error, i.e., the distances d, must be entered into the corresponding formulas, especially into equation (1). i and a i , replaced by the difference between the best refraction and the set or applied correction.

[0222] The embodiments of models of a sensitivity metric described above are examples to illustrate how sensitivity can be determined within the scope of the present invention.

[0223] The target can be a real target (or real object) or a virtual target (or virtual object). Specifically, the target can be a real object or a virtually projected object (or a projected virtual object). A target can be realized, for example, by a display (e.g., with one or more lenses and / or one or more mirrors), by a light-field display, and / or by a badaloptometer (which allows for constant magnification despite changes in effect) and projected onto at least one eye of the subject.

[0224] A "virtual object" or "virtual target" is understood to be, in particular, an optical imaging system that generates wavefronts emanating from virtual object points, such that these wavefronts strike at least one eye of the subject. The wavefronts generated by the virtual target (each corresponding to a virtual object point) and striking at least one eye of the subject can have an adjustable spherical curvature and / or an adjustable cylindrical curvature component, wherein the cylindrical curvature component is preferably adjustable both with respect to the magnitude of the curvature and with respect to the axis position.

[0225] Preferably, the virtual position of the virtual object (target) can be changed so that different accommodation states of at least one eye can be stimulated. In particular, the position of the virtual object can preferably be changed between a position for stimulating distance accommodation and a position for stimulating near accommodation. Additionally, the position of the virtual object can preferably be adjusted such that at least one eye of the subject is no longer able to accommodate to the virtual object. In this case, the virtual object (target) can only be perceived as blurry by the subject in all directions. This results in the relaxation of the ciliary muscles. Such a state is referred to as a "fogged" state.

[0226] A target is projected into at least one eye of the subject with an adjustable or variable target refraction (or target effect). This projection can be achieved using an optical system that can also adjust and / or vary the effect or refraction of the target, i.e., the target refraction. Within the scope of this invention, "target refraction" is thus understood to mean the refraction (in particular spherical and / or astigmatic refraction) applied or caused by the optical system with which the target is projected into at least one eye of the subject, or with which the target is presented to at least one eye of the subject.

[0227] The target is defined as an optical projection into or onto the subject's eye, such that this projection creates an image on the retina that corresponds to the image of a real object at a specific distance from the eye. This specific distance is also referred to as the virtual position for the virtual target. In other words, a target, as described here, is an image of an object projected onto at least one of the subject's eyes. A backlit slide, for example, can be used as the object. Since the target in the case of a virtual target is not (directly) a real object at the virtual position, a suitable design of the optical system for projection can also simulate a virtual position beyond infinity. This corresponds to wavefronts that converge towards the eye (i.e., in the direction of propagation).

[0228] The projection of a target (in particular a virtual target) into at least one eye of the test subject using an optical system is generally known, so it will not be discussed in detail within the scope of the present invention. For example, the projection of a target into at least one eye of the test subject is described in K. Nicke and S. Trumm: “Spectacle Lenses of the Future - Step 3 The DNEye Scanner”, Der Augenoptiker, June 2012, or also in German patent application DE 102013 000 295 A1.

[0229] The target projected into at least one eye of the subject is designed to verify a given, in particular predetermined and / or known, visual acuity (or a given visual acuity level). "Verifying a given visual acuity" here means, in particular, that the target can be used to determine or ascertain (especially based on a subject action) whether at least one eye of the subject achieves the given visual acuity or visual acuity level. In other words, the target specifies a particular visual acuity or visual acuity level, the attainability of which for at least one eye of the subject can be determined (especially based on a subject action). Specifically, the target is designed (in particular, dimensioned) in such a way that a given visual acuity or visual acuity level can be assigned to it.In other words, the target is a target with a predetermined visual acuity or visual acuity level. This means that the subject, particularly with ideal refraction or correction of any refractive error in at least one of the subject's eyes, can recognize or identify the target, provided that at least one of the subject's eyes achieves or exhibits at least the visual acuity or visual acuity level specified by the target. This visual acuity level is linked to and / or dependent on the dimension of the directional feature of the adapted optotype.

[0230] In particular, the target can include or be a customized optotype suitable for determining visual acuity. The dimension or size of the directional feature of the optotype depends on the predetermined visual acuity or visual acuity level. Specifically, the dimension or size of the directional feature of the optotype is chosen such that only a subject with a visual acuity at least equal to the predetermined visual acuity or visual acuity level can recognize and / or identify the directional feature of the optotype.

[0231] The target can also be an image or photograph containing two or more details, the recognition of which can be assigned to a specific visual acuity or visual acuity level. The image can, in particular, depict objects (such as a road stretching to infinity, a sky, a distant balloon, etc.) that can evoke a sense of vastness or distance in the viewer. The details mentioned above, contained in the image (such as symbols or fabric panels on a hot air balloon or the basket of a hot air balloon, clouds or symbols on clouds, lines on a road, symbols on roadside signs, etc.), are explicitly included in the term "optical symbol" within the scope of this description. A particularly suitable symbol as an optotype comprises, for example, one or more concentric rings that merge into a circle at a given level of blur.

[0232] The determination of the visual acuity or visual acuity levels of a target, target or optotype can, as is known, be done, for example, by calculating the visual angle of details, or by recognizing subjects with known visual acuity characteristics.

[0233] After projecting the target into at least one eye of the subject, a visual acuity limit refraction corresponding to the specified visual acuity or visual acuity level is determined for at least one eye of the subject.

[0234] The term "visual limit refraction" or "visual level limit refraction" refers to the refraction at which the target's identifiability changes for the subject. Specifically, "visual limit refraction" or "visual level limit refraction" refers to the refraction at which the subject can no longer see the target presented to them or the virtual target projected into at least one eye, which is characterized by a predetermined visual acuity or visual level. a) starting from a nebulized state by varying the target refraction (applied or caused by the optical system) can detect and / or identify for the first time, or b) starting from an unfogged state, by varying the target refraction (applied or caused by the optical system) it can no longer detect and / or identify.

[0235] The visual acuity limit is determined by varying the target refraction of the target projected into at least one eye of the subject and by detecting a subject action (e.g., a message or input from the subject, in particular the pressing of a button or joystick). The variation of the target refraction can be stepwise or, preferably, continuously. Preferably, the variation of the target refraction is monotonous and / or continuous. The subject action signals or indicates that the identifiability of the target for the subject has changed at the time of the action. In other words, the subject signals, by means of the action, that they can recognize or identify the target for the first time, or can no longer recognize or identify it, given the target refraction present at the time of the action.In particular, the visual acuity limit refraction corresponds to the target refraction or target effect present at the time of the subject's action or applied by the optical system.

[0236] Thus, the sensitivity of at least one eye of the subject is determined, taking into account the given visual acuity or visual acuity level and the corresponding visual acuity limit refraction. For this purpose, adapted optotypes can be used, the dimension of which corresponds to the given visual acuity values ​​or levels.

[0237] This method can be performed particularly within the framework of autorefractometric or aberrometric measurements. For this purpose, at least one pair of visual acuity level and corresponding applied correction is recorded. This is achieved by a signal from the subject during the change in the applied correction on a target with a defined visual acuity level (i.e., a defined size of a visual symbol).

[0238] As mentioned previously, determining sensitivity requires at least two pairs of visual acuity level and corresponding applied correction. Conventional methods determine the visual acuity level achieved by the subject with each defined applied correction (i.e., the minimum size at which the subject can still recognize the optotype). In this variant of the procedure, however, the dimension of the directional feature of the adapted optotype (and thus the visual acuity level) remains constant for at least one of these pairs, while the applied correction is varied. The subject signals when they can just barely, or no longer, recognize an adapted optotype of a defined size.

[0239] In contrast to the state of the art, this alternative does not require the visual acuity level for a specific applied effect – with a priori known or a priori unknown refractive error – to determine the sensitivity, but rather the applied effect required to achieve a given visual acuity.

[0240] This approach allows for the simple and rapid determination of sensitivity. In particular, it enables the sensitivity (as a subjective measurement) to be determined easily and without significant additional effort during a standard objective refraction measurement. Specifically, it avoids the need for complex measurements during subjective refraction and eliminates the psychologically challenging step of having the subject perform visual tasks with a weaker correction after the optimal refraction has been determined. Furthermore, this approach can be advantageously combined with other measurements to determine individual parameters for advanced lenses (e.g., near vision testing, pupillometry, keratography) and for optometric or ophthalmological screening, as well as with measurements for generating reports (such as keratography, opacity, pachymetry, tomography, tonometry, or retinal imaging).

[0241] In one embodiment, before projecting a target designed to verify (or determine) a predetermined visual acuity into at least one eye of the subject, an objective and / or subjective refraction result (in particular, a combined refraction result based on objective and subjective measurements, which also includes further data such as low- and / or high-order aberrations from aberrometry or other biometric data such as corneal shape, lens-retinal distance, anterior chamber depth, etc.) is determined for at least one eye of the subject. A "refraction result" is understood to mean, in particular, a determined refractive value. In this way, unlike the previous approach, the determination of sensitivity can be combined with one or more aberrometric or autorefractometric measurements.In particular, the determination of visual acuity can be combined with the measurement of autorefractometric or aberrometric data in the non-accommodated and accommodated states.

[0242] Preferably, the objective refraction value or result is determined under a fogged condition. For this purpose, a target (e.g., an image or photograph) can be presented to the subject, or a corresponding virtual target can be projected into at least one of the subject's eyes (using the optical system). This target has an effect that causes the subject to perceive the target only as blurred (or not completely sharp), thereby relaxing the ciliary muscle of at least one of the subject's eyes. Such fogging can be achieved, for example, with an additional effect of approximately 1.25 to 1.5 diopters compared to the optimal refraction of at least one of the subject's eyes.

[0243] In a special embodiment, the accommodation state of the eye can also be monitored in order to obtain even more reliable values ​​for sensitivity.

[0244] Preferably, before varying the target refraction, the target is projected into at least one of the subject's eyes with a starting target refraction—that is, the initial optical effect applied, at least in the selected preferred direction—such that the subject can only perceive the target as blurry (or not completely sharp) and / or cannot identify it. In other words, a starting target refraction is preferably chosen such that the subject cannot focus the target or the adapted optotype through accommodation. This is achieved, in particular, by shifting the starting target refraction towards the positive direction compared to the optimal refraction of at least one of the subject's eyes. Only by changing the target refraction towards the negative direction can a state be reached in which the subject can perceive and / or identify the target or optotype.This has the additional advantage that the subject does not initially know the target or optotype and is therefore more likely to perform the action at the correct time, namely only when they can actually identify the target or optotype. If, on the other hand, the subject already knows the target or optotype beforehand or at the beginning of the measurement (due to a corresponding initial target refraction with which they see the target or optotype clearly), it has been recognized within the scope of the present invention that while such a procedure is possible as an alternative, it may be inferior to the preferred embodiment mentioned above in terms of accuracy and reliability. This is because a subject who already knows the target or optotype in advance often tends to misjudge the point in time at which, after varying the target refraction towards plus, they can see the target or optotype clearly.Visual acuity signs are no longer recognized and / or can no longer be identified, signaling something too late.

[0245] In a further embodiment, the method comprises, either before or after the steps of projecting a target designed to verify a predetermined visual acuity into the subject's at least one eye and determining a visual acuity limit refraction corresponding to the predetermined visual acuity of the target, determining an optimal refraction (target refraction) of the subject's at least one eye. In particular, the method may include determining an objective and / or subjective refraction or an objective and / or subjective refraction result. Determining an optimal refraction may also include determining a combined refraction or a combined refraction result based on an objective and / or subjective refraction measurement, in which, in particular, further data such as low- and / or high-order aberrations from aberrometry are also taken into account.Further biometric data (such as corneal shape, lens-retinal distance, anterior chamber depth, etc.) of at least one eye of the subject must be taken into account. In this sense, the terms "refraction" and "target refraction" (or "refraction result") in the context of "optimal refraction" should not be limited to corrections of low-order aberrations (e.g., sphere and astigmatism), but can also include higher-order aberrations. Therefore, the term "refraction" could also be understood more generally as "correction." Preferably, the optimal refraction of at least one eye of the subject is determined in a fogged state, which can be achieved by holding a suitable target in front of or projecting a suitable target into the subject's eye (see above).Furthermore, according to this preferred embodiment, the visual acuity achieved by at least one eye of the subject after compensation of any refractive error in that eye (e.g., based on a determined optimal refraction) is determined. In other words, the visual acuity is determined after the refractive error determined by the refraction measurement has been substantially corrected using an optical system or lenses whose effect corresponds to the determined refraction result; that is, the visual acuity cum correctione (VCC). The visual acuity can be determined using known methods. In particular, the determined optimal refraction and the measured corresponding visual acuity represent one of the at least two provided visual acuity-refraction value pairs that are used or considered in determining the sensitivity.In this way, it is possible to combine or integrate sensitivity determination with measurements of objective and / or subjective refraction. Sensitivity can thus be determined quickly and easily, especially in conjunction with other measurements.

[0246] In a further embodiment, the method, preferably after projecting a target designed to verify a predetermined visual acuity into at least one eye of the subject and after determining a visual acuity limit refraction corresponding to the predetermined visual acuity of the target, further comprises the following steps: - Determining a subjective refraction result or a subjective refraction for at least one eye of the subject; - Determining the visual acuity achieved by at least one eye of the subject when compensating for any refractive error of at least one eye of the subject, based on the determined subjective refraction result.

[0247] The determined subjective refraction and the visual acuity of at least one eye of the subject determined during this subjective refraction preferably represent one (or another, in particular a second, third, fourth, etc.) of the visual acuity-refraction value pairs provided by the procedure for determining the sensitivity.

[0248] Furthermore, the procedure preferably includes determining the optimal refraction of at least one eye of the subject based on the subjective refraction result and an objective refraction result. The optimal refraction is, in particular, a combined refraction derived from the subjective and objective refraction results. Determining a combined refraction result from objective and subjective refraction measurements is generally known and is therefore not explained in detail within the scope of this description. For example, a combined refraction can be determined by first performing an objective refraction measurement and then adjusting the objective refraction result using a subsequent subjective refraction. In particular, it is also possible to determine a combined refraction by calculating the average of the objective and subjective refractions.

[0249] In a further embodiment, the sensitivity is determined based on at least one calculated refraction error, wherein the at least one calculated refraction error is calculated based on a determined optimal refraction. The optimal refraction can be a determined objective and / or subjective refraction. In particular, the optimal refraction can represent a combined refraction of an objective and a subjective refraction.

[0250] Preferably, the refractive error is determined "ex-post," that is, only after projecting a target designed to verify a predetermined visual acuity into at least one eye of the subject, and after determining a visual acuity limit refraction corresponding to the predetermined visual acuity of the target. Preferably, the refractive error is determined only after determining at least one visual acuity-refraction value pair. Preferably, the refractive error is determined after performing an objective and / or subjective refraction measurement, and in particular after determining an ideal refraction or an ideal refraction result from an objective and subjective refraction measurement. For example, in a preferred embodiment, the following steps can be performed, particularly in the specified order: 1) Performing an objective refraction measurement (within the framework of the procedure according to the invention); 2) Determining at least one visual acuity-refraction value pair (within the framework of the procedure according to the invention); 3) Performing a subjective refraction measurement; 4) Determining an ideal refraction or refraction result from objective and subjective refraction measurements; and 5) Calculating the refraction errors and sensitivity based on the result from step 4, i.e., on the basis of the determined ideal refraction or the determined ideal refraction result.

[0251] In another embodiment, varying the target refraction includes a monotonous decrease in the target refraction and / or a monotonous increase in the target refraction.

[0252] In another embodiment, the visual limit refraction corresponding to the predetermined visual acuity of at least one eye of the subject is determined by lowering the target refraction and recording a subject action during this lowering, and / or by increasing the target refraction and recording a subject action during this highering. With each subject action, it is determined that the identifiability of the target for the subject has changed at the time of the respective action. In this way, the "point of blurring" is approached from different directions. In other words, one point of blurring can be determined when increasing the target refraction and another point of blurring when decreasing it. These points of blurring can differ from each other and can subsequently be averaged.In particular, the sensitivity can be determined from both uncertainty points by minimizing the squared error using known metrics.

[0253] In another embodiment, at least two of the provided visual acuity-refraction value pairs are provided by the following steps: - Projecting a first target with a first adjustable and / or variable target refraction into at least one eye of the subject, wherein the first target is designed to verify a predetermined (predetermined and / or known) first visual acuity (or a predetermined first visual acuity level); - Determining the first visual acuity limit refraction of at least one eye of the subject corresponding to the given first visual acuity (or the given first visual acuity level) by varying (in particular continuously, monotonously and / or steadily varying) the first target refraction of the first target projected into at least one eye of the subject and recording a first subject action that signals or establishes that the identifiability of the first target for the subject has changed at the time of the first subject action; - Projecting a second target with a second adjustable and / or variable target refraction into at least one eye of the subject, wherein the second target is designed to verify a predetermined (predetermined and / or known) second visual acuity (or a predetermined second visual acuity level) that differs from the predetermined first visual acuity (or the predetermined first visual acuity level); - Determining a second visual acuity limit refraction of at least one eye of the subject corresponding to the given second visual acuity (or the given second visual acuity level) by varying (in particular continuously, monotonously and / or steadily varying) the second target refraction of the second target projected into at least one eye of the subject and recording a second subject action that signals or establishes that the identifiability of the second target for the subject has changed at the time of the second subject action.

[0254] In particular, the sensitivity of at least one eye of the subject is determined using or considering the predetermined first visual acuity and the corresponding first visual acuity limit refraction, as well as using or considering the predetermined second visual acuity and the corresponding second visual acuity limit refraction. Preferably, the first predetermined visual acuity or the first predetermined visual acuity level of the first target is lower than the second predetermined visual acuity or the second predetermined visual acuity level of the second target. For example, the first predetermined visual acuity or the first predetermined visual acuity level may have a value of 0.8 logMar, while the second predetermined visual acuity or the second predetermined visual acuity level has a value of 1.0 logMar. Or, for example, the first predetermined visual acuity or the first predetermined visual acuity level may have a value of 0.4 logMar, while the second predetermined visual acuity or the second predetermined visual acuity level may have a value of 0.0 logMar.The second predefined visual acuity level has a value of 0.8 logMar or 1.0 logMar. It is understood that other values ​​can also be selected. Preferably, the change in the predefined visual acuity or visual acuity level from one virtual target to the next target is in the range of 0.2 logMar to 0.7 logMar, more preferably in the range of 0.2 logMar to 0.5 logMar, and most preferably in the range of 0.2 logMar to 0.3 logMar.

[0255] In another embodiment, determining a visual acuity limit refraction involves measuring and / or monitoring the accommodation state of at least one eye of the subject, wherein the measurement of the accommodation state is performed, in particular, at least at the time of or immediately after the subject's action. The results of such a measurement or monitoring can be used to control the procedure (e.g., aborting or repeating individual steps in the event of unwanted accommodation (e.g., exceeding a certain threshold)). The measurement can be performed continuously or only at or immediately after the subject's action. Furthermore, an accommodation state (sphere, cylinder, low- or high-order aberrations) measured, ideally at the time of the subject's action, can be included in the calculation of the sensitivity or the refractive error.For example, the amount of accommodation can be subtracted from the distance of the applied correction to the refractive value for distance vision. Expressed as formulas, in the simplest case, the following applies: Sensitivity represents the visual acuity V as a function f of the refractive error F, i.e., V = f(F). Here, F is the refractive error. - without accommodation, the difference between the actual applied action T and the ideal action I, i.e., F = T - I; and - accommodation is the difference between the actual applied effect T and the currently measured effect G a , so F = T - G a .

[0256] If there is a deviation D between the ideal effect I and the measured effect with a relaxed eye (effect G0), then: I = G0 + D. Accordingly, in this situation, F = T - (G0+D) or F = T - (G a+D). For spherical values, this formula can be used as described. For cylindrical values, the cross-cylinder formula should be used accordingly. Zernike coefficients (also for higher-order aberrations) or power vectors can be used analogously.

[0257] Alternatively or additionally, determining the visual acuity limit refraction can include measuring and / or monitoring the pupil size (e.g., pupil radius) of at least one of the subject's eyes, with the pupil size measurement being performed at least at the time of, or immediately after, the subject's action. The pupil size can be measured, for example, using a camera that is part of a refraction unit, such as an autorefractor or aberrometer, or using a separate camera. The pupil size measured at the time of the subject's action (i.e., at the point of blur) or shortly before or after (e.g., up to 2 seconds before reaching the point of blur) can be used to determine the sensitivity of at least one of the subject's eyes to blur.In particular, the measured pupil size can be used to quantify the blurring of the image on the retina, preferably with the aid of a suitably parameterized eye model and a known additional fogging. Instead of a complete eye model, a simpler description can also be used. For example, the angle at which the dispersion disk of a blurred point can be observed for a given pupil size and additional fogging can be calculated (see, for example, WO 2019 034525 A1). Within such a visual acuity model, the sensitivity can be determined as the decrease in visual acuity per unit angle of the dispersion disk.

[0258] In a further embodiment, to determine a visual acuity limit refraction, the subject is presented with a visual task offering at least two, preferably at least three, particularly preferably at least four, and especially four or eight, possible different answers, whereby the subject can answer the visual task based on the subject's action. A "visual task" here is understood to be, in particular, a task that has a predetermined and therefore verifiable solution. Specifically, the visual task is thus a verifiable task (i.e., a visual task whose solution is known and therefore verifiable). In other words, the subject's action goes beyond simply communicating the recognizability or identifiability of the target. Preferably, the visual task is based on a forced choice, i.e., the subject is "forced" to make a selection from several or more possible answers.The task involves making at least two or a multitude of possible answers, with the correct answer preferably being predetermined or known. Such a visual task is referred to as a "forced choice" visual task. Solving the visual task, or making a selection, can be done, for example, using a joystick that allows the subject to control different directions. For instance, the visual task might involve the subject using a joystick to identify the position or direction of the gap in a fitted visual symbol. If the fitted visual symbol is, for example, a Landolt ring, there are two possible positions and thus two possible answers for the subject, indicating how the directional feature can be positioned parallel to the selected preferred direction. It goes without saying that other visual symbols can also be used, so the subject's answers may depend on the fitted visual symbol.In this way, the procedure becomes more accurate and reliable than if the test subject only had to give an unverified response (e.g., "yes" or "no" or "recognizable" or "not recognizable").

[0259] In a further embodiment, prior to the step of determining a visual acuity limit refraction, initial aberrometric data of at least one eye of the subject are acquired, preferably for a distance accommodation state and / or a foggy state of at least one eye of the subject, and particularly at a first brightness level. Furthermore, the method preferably comprises acquiring second aberrometric data of at least one eye of the subject for a near accommodation state of at least one eye of the subject, particularly at a second brightness level, the value of which is lower than that of the first brightness level. The acquisition of the second aberrometric data preferably takes place prior to the step of determining a visual acuity limit refraction. In the context of this description, "aberrometric data" (or "aberrometric data") refers to the following:"Aberrometric measurements" are understood to mean data for describing the aberrations of an eye (measurements for obtaining this data), the information content of which corresponds at least to the term of the order "defocus" when represented with Zernike coefficients, but ideally includes higher orders (e.g., coma and spherical aberrations). In particular, the "aberrometric data" can also include or be (purely) autorefractometric data. Specifically, the acquisition of aberrometric data also includes the acquisition of (purely) autorefractometric data (i.e., sphere and / or cylinder and / or axis). The first and second brightness values ​​are preferably each in the mesopic vision regime (preferred luminance in the range of approximately 0.003 cd / m²). 2 up to about 30 cd / m 2 , particularly preferably in the range of approximately 0.003 cd / m² 2 up to about 3 cd / m 2 , even more so in the range of approximately 0.003 cd / m² 2up to approximately 0.3 cd / m 2 , most preferred in the range of approximately 0.003 cd / m² 2 up to approximately 0.03 cd / m 2 ) provided. Brightness is always understood to mean, in particular, the brightness at the location of the eye or the brightness that can be perceived by the eye.

[0260] Along with the acquisition of initial aberrometric data and / or the acquisition of secondary aberrometric data (i.e., particularly at the first and second brightness levels and the first and second accommodation states), initial and secondary pupillometric data can also be acquired for at least one eye of the subject. The term "pupillometric data" (or pupillometric measurements) refers to information about the size of the pupil (or measurements used to obtain this data), which includes at least one dimension (e.g., a radius) but can also describe the shape of the pupil in a more complex way. Additionally, the pupillometric data can contain information about the position of the pupil (e.g., relative to the corneal vertex or the optical axis of the eye).

[0261] Another aspect concerns a method for calculating, optimizing or evaluating a spectacle lens for at least one eye of a subject or spectacle wearer, taking into account the sensitivity of the subject's at least one eye, wherein the sensitivity of the subject's at least one eye is determined by one of the methods according to the invention.

[0262] In particular, the procedure for calculating, optimizing, or evaluating a spectacle lens for at least one eye of a test subject may include the following steps: a) Providing an assignment of at least one imaging property or aberration of a spectacle lens system to the visual acuity of the spectacle wearer or of an average spectacle wearer when viewing an object through the spectacle lens system; b) Determining or specifying an objective function for the spectacle lens to be calculated or evaluated, in which the assignment from step (a) is to be evaluated; c) Calculating or evaluating the spectacle lens to be calculated or evaluated by evaluating the objective function, whereby the objective function is evaluated at least once.

[0263] The assignment of at least one imaging property or aberration of a spectacle lens system to the visual acuity of the wearer can depend parametrically on the measured initial visual acuity and / or the measured sensitivity of the wearer. Calculating and / or optimizing the spectacle lens can, in particular, include minimizing or maximizing the objective function. Furthermore, the method for calculating, optimizing, or evaluating a spectacle lens can include calculating the path of at least one light beam emanating from the object for at least one viewing direction using wavefront calculation, ray calculation, or wavefield calculation through the spectacle lens system and / or through the spectacle lens to be calculated or evaluated, up to an evaluation surface within the spectacle lens system.Furthermore, the method for calculating, optimizing, or evaluating a spectacle lens can include calculating the difference between the light beam emanating from the object and a reference light beam converging on the retina of a model eye at the evaluation surface, and determining at least one imaging property or aberration based on the calculated difference. The calculation of at least one light beam emanating from the object is preferably performed by wavefront analysis, wherein calculating the difference at the evaluation surface includes calculating the wavefront difference between the wavefront of the light beam emanating from the object and the wavefront of the reference light beam converging on the retina, with the wavefront difference being calculated at the evaluation surface.Furthermore, the method for calculating, optimizing or evaluating a spectacle lens can include assigning a geometric-optical angle and / or a square shape in geometric-optical angle space to the calculated wavefront difference, wherein at least one imaging property or aberration depends on at least one component of the geometric-optical angle and / or the square shape.

[0264] Alternatively or additionally, the procedure for calculating, optimizing, or evaluating a spectacle lens may include the following steps: - Specifying a first surface and a second surface for the spectacle lens to be calculated or optimized; - Determining the path of a principal ray through at least one viewing point of at least one surface of the spectacle lens to be calculated or optimized into a model eye; - Evaluating an aberration of a wavefront resulting along the principal ray from a spherical wavefront incident on the first surface of the spectacle lens at an evaluation surface in comparison to a wavefront converging at a point on the retina of the eye model; - iteratively varying at least one area of ​​the spectacle lens to be calculated or optimized until the evaluated aberration corresponds to a predetermined target aberration.

[0265] Another aspect concerns a process for manufacturing a spectacle lens, comprehensively: - Calculating or optimizing a spectacle lens according to the inventive method for calculating or optimizing a spectacle lens; and - Manufacturing the calculated or optimized spectacle lens.

[0266] Furthermore, the invention provides a computer program product, particularly in the form of a storage medium or a data stream, containing program code designed, when loaded and executed on a computer, to perform a method according to the invention, in particular for determining the sensitivity of at least one eye of a test subject and / or for calculating, optimizing, or evaluating a spectacle lens and / or for manufacturing a spectacle lens. In other words, the invention provides a computer program product comprising machine-readable program code that, when loaded on a computer, is suitable for executing the method according to the invention described above. In particular, a computer program product is understood to be a program stored on a data carrier. Specifically, the program code is stored on a data carrier.In other words, the computer program product comprises computer-readable instructions which, when loaded into a computer's memory and executed by the computer, cause the computer to perform a method according to the invention.

[0267] In particular, the invention provides a computer program product which contains a program code that is designed and configured, when loaded and executed on a computer, to carry out an inventive method for determining the sensitivity of at least one eye of a test subject and / or an inventive method for calculating, optimizing or evaluating a spectacle lens and / or an inventive method for manufacturing a spectacle lens.

[0268] Another aspect concerns a device for determining the sensitivity of at least one eye of a subject, comprising: - a target delivery device for providing a target designed to verify a given visual acuity and configured to display at least one adapted optotype; - an optical system for projecting the target with a target refraction into at least one eye of the subject, wherein the optical system is designed to adjust and vary the target refraction; - a feedback unit for recording a subject action in order to determine that, at the time of the subject action, particularly as a result of varying the target refraction of the target projected into at least one eye of the subject using the optical system, the identifiability of the target for the subject has changed; and - a visual acuity limit refraction determination unit for determining a visual acuity limit refraction of at least one eye of the subject corresponding to the specified visual acuity, wherein the visual acuity limit refraction determination unit is designed to record (in particular to determine and store) the target refraction caused by the optical system at the time of the subject's action.

[0269] The target delivery device can include, for example, an electronic display or a digital screen. In particular, the display can be designed so that individual pixels, different areas, or different components of the display can be addressed individually, especially to display composite optotypes. For example, segments of a ring can be displayed, which can be used to generate or display Landolt C optotypes with differently oriented apertures. Alternatively or additionally, complete optotypes, such as letters or numbers, can also be designed as whole, and in particular switchable, LCD elements. Generally, the display is configured to show customized optotypes.

[0270] The target delivery device can, for example, include a folding, sliding, or rotating mechanism, such as magnetic or motorized, with which different targets or images can be displayed and / or exchanged. The targets or images can also be partially transparent and contain only areas that are to be displayed in addition to another image.

[0271] Transparent, backlit images can also be designed so that certain parts of the image are only visible when one or more specific light sources (e.g., in otherwise shaded areas or with special wavelengths) are switched on or off.

[0272] The optical system is positioned between at least one eye of the subject and the target delivery device or the target itself. The optical system may be configured as a refraction unit. It is designed to create different target effects as optical effects, at least in the selected preferred direction, thereby influencing the target's detectability for at least one eye of the subject. The optical system may be designed to provide various spherical effects. This can be achieved, for example, by arranging one or more spherical lenses, such as in a Badal system. Alternatively or additionally, one or more adaptive lenses, possibly in combination with conventional lenses, may be used.In more complex cases, the optical system can be designed to create or produce various cylindrical effects or higher-order effects in addition to or instead of spherical effects.

[0273] The optical system can include at least one lens with a spherical effect and / or at least one lens with a cylindrical effect.

[0274] For example, the optical system can comprise a magazine containing a variety of spherical and / or cylindrical lenses, each exhibiting different spherical or cylindrical effects, and the magazine can be designed and arranged such that individual spherical or cylindrical lenses and / or combinations of several spherical or cylindrical lenses from the magazine can be selected and used to project the target. The optical system can also, for example, include an Alvarez lens system. In other words, the subject is presented with a target (or a projected or virtual target) through which the subject sees the target or virtual target. The optical system can also, for example, include two lenses that can be rotated relative to each other, each with at least one cylindrical component in its effect.In particular, the optical system can comprise two cylindrical lenses with interlocking, mutually facing rotationally symmetrical surfaces, preferably planar surfaces. The optical system can also comprise a positive and a negative cylindrical lens with oppositely equivalent effects, which are rotatably mounted relative to each other and preferably slidably relative to each other.

[0275] Furthermore, the optical system may alter the target's viewing angle when applying different effects. This can either be prevented by appropriately designing the optical system or calculated and compensated for in the display. For this, the viewing angle must be determined as a function of the applied effect, and a visual acuity value assigned based on this actual viewing angle. This can be achieved, for example, by determining the magnification of the optical system and correspondingly reducing the size of the target. Alternatively, the optical system can be calibrated using a camera. By directly measuring the target size with a camera positioned in place of at least one of the subject's eyes (and looking into the optical system), the camera can be positioned to directly measure the target size.

[0276] The participant's feedback or action can, in principle, be verbal. In this case, a user can note the state of the optical system during the feedback or participant action and / or relay the feedback directly to the feedback system. However, this approach is prone to errors and causes delays. Therefore, direct feedback from the participant to the feedback system is preferred. In the simplest case, the feedback system can comprise a single button. In a further preferred embodiment, the feedback system can also comprise two buttons ("+" and "-"), three buttons ("+", "-", and "OK"), four buttons (e.g., "+", "-", "OK", and "Cancel"), etc., and / or a joystick. Alternatively or additionally, the feedback system can include a microphone for capturing verbal utterances from the participant.

[0277] In one embodiment, the device comprises an evaluation unit for determining the sensitivity of at least one eye of the subject based on at least two provided visual acuity-refraction value pairs. The visual acuity limit refraction determination unit can be a component of the evaluation unit. In other words, the evaluation unit can include the visual acuity limit refraction determination unit.

[0278] In a further embodiment, the device comprises an autorefractometric or aberrometric measuring unit for determining one or more objective refractions of at least one eye of the subject, wherein the autorefractometric or aberrometric measuring unit is preferably designed to measure and / or monitor the accommodation state of at least one eye of the subject. Furthermore, the autorefractometric or aberrometric measuring unit can include a camera for determining the pupil size (in particular, the pupil radius) of at least one eye of the subject. Alternatively or additionally, the autorefractometric or aberrometric measuring unit can include a calibration camera for calibrating the optical system.The camera for determining pupil size and the calibration camera can also be implemented in a single camera that combines both functions (determining pupil size and calibrating the optical system).

[0279] In a further preferred embodiment, the device comprises a pupil size measuring unit (in particular a camera) for determining the pupil size (in particular a pupil radius) of at least one eye of the subject. Alternatively or additionally, the device may include a lighting device for generating at least two brightness levels. Alternatively or additionally, the device may include a pupillometer device designed to acquire first pupillometric data of the at least one eye at a first brightness level and to acquire secondary pupillometric data of the at least one eye at a second brightness level.

[0280] Another aspect concerns a device for calculating, optimizing or evaluating a spectacle lens for at least one eye of a subject taking into account the sensitivity of the subject's at least one eye, comprising a device according to the invention for determining the sensitivity of the wearer's at least one eye.

[0281] The device for calculating, optimizing, or evaluating a spectacle lens may, in particular, include the following components: - a surface model database for specifying a first surface and a second surface for the spectacle lens to be calculated or optimized; - a principal ray determination module for determining the path of a principal ray through at least one viewing point of at least one surface of the spectacle lens to be calculated or optimized into a model eye; - an evaluation module for evaluating an aberration of a wavefront resulting along the principal ray from a spherical wavefront incident on the first surface of the spectacle lens at an evaluation surface in comparison to a wavefront converging at a point on the retina of the eye model; and - an optimization module for iteratively varying at least one area of ​​the spectacle lens to be calculated or optimized, until the evaluated aberration corresponds to a specified target aberration.

[0282] Another aspect concerns a device for manufacturing a spectacle lens, comprising: - Calculation or optimization means designed to calculate or optimize the spectacle lens according to a method according to the invention for calculating or optimizing a spectacle lens; and - Processing tools designed to process the spectacle lens according to the result of the calculation or optimization.

[0283] Another aspect concerns a spectacle lens which was produced by a method according to the invention for producing a spectacle lens and / or by means of a device according to the invention for producing a spectacle lens.

[0284] Furthermore, the invention offers a use of a spectacle lens manufactured according to the manufacturing process of the present invention, in particular in a preferred embodiment, in a predetermined average or individual position of use of the spectacle lens in front of the eyes of a specific spectacle wearer for the correction of a visual impairment of the spectacle wearer.

[0285] In particular, a computer-implemented method according to the invention can be provided in the form of ordering and / or industry software. Specifically, in such a method, the data required for the calculation and / or optimization and / or manufacture of a spectacle lens can be acquired and / or transmitted.

[0286] An inventive device and / or system, e.g., for ordering a spectacle lens, may in particular comprise a computer and / or data server designed to communicate via a network (e.g., the Internet). The computer is in particular designed to execute a computer-implemented method, e.g., ordering software for ordering at least one spectacle lens, and / or transmission software for transmitting relevant data, and / or determination software for determining relevant data, and / or calculation or optimization software for calculating and / or optimizing a spectacle lens to be manufactured, according to the present invention.

[0287] The following section describes individual embodiments for solving the problem based on the Fig. Figures 6-8 are described by way of example. Some of the described embodiments exhibit features that are not strictly necessary to carry out the claimed subject matter, but which provide desirable properties in certain applications. Thus, embodiments that do not possess all the features of the embodiments described below are also considered to be disclosed within the scope of the described technical teaching. Furthermore, to avoid unnecessary repetition, certain features are mentioned only in relation to some of the embodiments described below. It should be noted that the individual embodiments should therefore not only be considered individually, but also in combination. From this combination, the person skilled in the art will recognize that individual embodiments can also be modified by incorporating one or more features from other embodiments.It should be noted that a systematic combination of the individual embodiments with one or more features described in relation to other embodiments may be desirable and useful and should therefore be considered and also be regarded as covered by the description.

[0288] The Fig. Figure 6 shows an exemplary image or photograph, which includes a hot air balloon and a road and conveys a sense of distance to the viewer. Such an image can, for example, be projected as a target (in particular as a virtual target) into at least one eye of a test subject within the scope of the present invention, in order to carry out an objective refraction measurement, for example, in a foggy state in which the test subject can only perceive the image or details of the image in a blurred manner.

[0289] The Fig. Figure 7 shows the image or photo of Fig. 6. An image is presented with exemplary, adapted optotypes integrated into or superimposed on the image for a selected preferred direction. Each of these adapted optotypes has a predetermined visual acuity or visual acuity level. In the inventive method, the image with the adapted optotypes is provided with an adjustable target refraction using an optical system. This target refraction is varied by means of the optical system, and the subject signals, by means of a subject action, that the identifiability of the target or the adapted optotypes has changed for them at the time of the subject action. In this way, visual acuity-refraction value pairs can be provided to determine the sensitivity of at least one eye of the subject.

[0290] One or more targets can be presented to the subject or projected as virtual targets into at least one of the subject's eyes. Depending on the design, two or more targets can be used, which can also be identical in content.

[0291] For example, a first target could be an image that conveys a sense of distance (see e.g. Fig. 6), a second target one or more adapted optotypes in a specific size, and a third target one or more adapted optotypes in a different size.

[0292] Alternatively, the first target can be an image that conveys a sense of distance, while the second and third targets can be identical in content and contain one or more adapted optotypes in one of two sizes each.

[0293] Alternatively, all three targets can be identical and represent an image that conveys a sense of distance but includes one or more details, the recognition of which can each be assigned to a specific visual acuity level. These details are explicitly included in this description by the term "adapted optotype." Examples of such details in an image containing, for example, a hot air balloon and a road are: - Symbols or fabric panels on the hot air balloon, as well as the basket of a hot air balloon, - Clouds or symbols on clouds, - Lines on a road, and / or - Symbols on signs at the roadside.

[0294] A particularly suitable symbol, for example, has one or more concentric rings which merge into a circle at a given level of blur.

[0295] In contrast to the prior art, these embodiments do not determine the visual acuity level for a specific applied effect, but rather the applied effect required to achieve a predetermined visual acuity. Furthermore, the determination of visual acuity can be combined with the measurement of autorefractometric or aberrometric data in the non-accommodated and accommodated states. In a special embodiment, the accommodation state of the eye can also be monitored to obtain even more reliable sensitivity values. A. Procedure according to an exemplary embodiment without subjective refraction

[0296] An examination of the subject subject can take place, for example, as follows: 1) Using autorefractometric or aberrometric measurements, the subject's objective refractive value is determined. For this, the subject is presented with an initial target. A suitable optical system then creates an initial effect that prevents the subject from seeing the target clearly, thereby inducing relaxation of the ciliary muscles. 2) A second target is then presented to the subject, and a second effect is applied using the optical system. This effect is designed so that a subject with high visual acuity cannot recognize at least one of the adjusted optotypes. This is achieved primarily by selecting a spherical effect as the applied optical effect, corresponding to the middle sphere or one of the two principal meridians of the objective refractive value, plus an additional positive optical effect. This latter effect—often called "fogging"—is chosen because the subject cannot compensate for it through accommodation. Standard values ​​based on mean values ​​for a large number of subjects can be used to determine the rate at which the applied optical effect is changed. For example, it is known that visual acuity is approximately halved with a 0.5 diopter spherical effect or a 1 diopter cylinder effect.Preferably, the target refraction is varied as an applied optical effect at a rate between 1 / 16 diopters per second and 1 / 2 diopter per second. The additional optical effect can also depend on the pupil size measured by the aberrometry unit. For example, it can be inversely proportional to the pupil radius, so that subjects with smaller pupils are preferably fogged with a stronger effect than subjects with larger pupils to ensure that the blurring perceived by all subjects is similar. 3) Alternatively, a spherocylindrical effect can be applied as the optical effect. For example, a cylindrical effect for the optical system can be derived from the objective refraction, and a mean objective refraction value can be superimposed with an additional positive spherical effect. Alternatively or additionally, the objective refraction value can be superimposed with an astigmatic offset (so-called astigmatic nebulization). The optical effect is then slowly changed (e.g., between 1 / 16 diopters per second and 1 / 2 diopter per second) towards optimal or objective refraction (by varying the spherical and / or astigmatic effect). 4) As soon as the subject can recognize the directional feature of the adjusted optotype of the second target by changing the applied optical effect, they indicate this (e.g., by pressing the "OK" button). If necessary, they can adjust the limiting effect themselves (e.g., using the "+" and "-" buttons) and confirm it (e.g., also by pressing the "OK" button). The effect set in this way is saved as the "visual limiting effect" or "visual limiting refraction" upon recognition of the second target. 5) The third target is presented to the subject. 6) The optical power is now changed further slowly (e.g. between 1 / 16 dpt per second and 1 / 2 dpt per second) towards the optimal or objective refraction value (by varying the applied optical power). 7) As soon as the subject can recognize the directional feature of the adjusted optotype of the third target by changing the applied optical effect, they indicate this (e.g., by pressing the "OK" button). If necessary, they can adjust the limiting effect (e.g., using the "+" and "-" buttons) and confirm it (e.g., also by pressing the "OK" button). The effect set at this point is saved as the "visual limiting effect" or "visual limiting refraction" upon recognition of the third target.

[0297] The sensitivity can be determined from the visual acuity levels of the two targets, more precisely, the two respective dimensions of the directional features of the two adapted optotypes, the objective refractive value, the applied optical effect when recognizing the second target, and the applied optical effect when recognizing the third target. For this purpose, a sensitivity metric, such as that described above in exemplary embodiments, can be used. The refractive errors result from the (e.g., spherical and / or astigmatic) difference between the applied optical effect when recognizing each target and the objective refractive value. B. Procedure according to an exemplary embodiment with subjective refraction

[0298] In this variant, steps 5) to 7) from the procedure described in section A can be omitted. Only the visual acuity for a target and the applied optical effect when recognizing (e.g., the directional features) of a target need to be determined. A subjective refraction measurement is then performed, determining the subjective refractive value and the visual acuity (visus cum correctione, VCC) achieved by the subject. The objective refractive value can be used as a starting point for the subjective refraction measurement.

[0299] Alternatively, the subjective refraction determination with visual acuity measurement can be performed before the steps in section A. In this case, the autorefraction or aberrometry and the determination of the objective refractive value (step 1) can be omitted, and the subjective refractive value can be used instead.

[0300] The refraction error can be calculated as the spherical or astigmatic difference between the effect when the target is detected and the subjective refraction value.

[0301] Instead of the subjective refractive value, a combined refractive value can also be used to calculate sensitivity or refractive error. This can be calculated based on the subjective refractive value and the objective refractive value, or other data (e.g., low- or high-order aberrations from aberrometry, or other biometric data such as corneal shape, lens-retinal distance, and anterior chamber depth). C. Adjusting the visual acuity level of a target

[0302] Furthermore, at least one visual acuity level of the adapted optotype(s) of a target can be adjusted to the individual subject. This is useful, for example, if the subject's astigmatism cannot be corrected. The visual acuity level(s) of the (virtual) target can then be chosen so that the target can still be recognized despite the refractive error remaining due to the astigmatism.

[0303] Information about visual acuity (e.g., visual acuity with correction or visual acuity without correction, for example, from subjective refraction testing) can also be incorporated into the determination of the target size, i.e., the dimension of the directional feature of the adapted optotype of the target.

[0304] If the subject cannot recognize the directional feature of the adapted optotype despite a slight deviation of the applied optical effect from the objective, subjective or combined refraction value, a lower visual acuity level can be used and the corresponding step repeated with a lower visual acuity level.

[0305] Additionally or instead, the findings from step 4 can be used to determine the visual acuity level in step 6.

[0306] To prevent the subject from already knowing the adapted optotype during multiple measurements or when switching eyes, at least one adapted optotype, symbol, or detail in the image can be changed between different measurements or when switching eyes. In particular, the selected preferred direction can be adjusted to the astigmatism of the other eye, or a change can be made from an adapted Landolt ring to an adapted Snellen E. Naturally, electronic displays are particularly well-suited as target delivery devices for this purpose. D. Finding the point of blur and adjusting the effect by the subject. Finding the point of blur.

[0307] As an alternative to the procedure in the previous sections, the optical effect provided at the beginning (i.e., in step 2) according to section A or B) can also be an effect that allows the recognition of the directional feature of the adapted optotype of the target. This can be an objective, subjective, or combined refractive value.

[0308] In steps 5 and 6, the applied optical stimulus is moved away from the original optical stimulus in the positive direction. This direction is chosen to prevent accommodation. In steps 4 and 7, the subject then signals the point in time at which they can no longer perceive the directional feature of the optotype.

[0309] If, analogous to the procedure in Section A, the applied optical effects for two visual acuity levels are determined, in this case the applied optical effects for the higher visual acuity level can first be determined (steps 2-4) and then (steps 5-7) for the lower visual acuity level. This allows the refractive error to be increased during the procedure, whereby first the directional feature of the adjusted optotype with the more difficult recognition (higher visual acuity level) and then the one with the easier recognition (lower visual acuity level) becomes unrecognizable. Correcting the (un)focus point

[0310] Optionally, in steps 4) and 7) of the above embodiments, the subject can correct the applied (i.e., created) optical effect if they are unsure whether they have signaled the correct time or the correct applied optical effect. This can be done, for example, using the "+" and "-" buttons of the feedback unit. Adjusting the (un)focus point by the test subject

[0311] The subject can also be asked directly to adjust the visual effect at which recognizing the directional feature of the fitted visual acuity symbol is either just barely possible or no longer possible. This can be done, for example, using the "+" and "-" buttons on the feedback unit. Approaching the (un)focus point from different directions

[0312] Furthermore, a point of uncertainty can be determined for increasing the value and another for decreasing it. These points can be different from each other and subsequently averaged. Alternatively, the sensitivity can be determined from both points of uncertainty by minimizing the squared error using known metrics. Repeat the measurement

[0313] Of course, the determination of the uncertainties can also be carried out several times in order to increase the measurement accuracy of the procedure. Monitoring of the accommodation state

[0314] During steps 3), 4), 6), and 7), in the procedure according to Section A, or during steps 3) and 4) in the procedure according to Section B, the accommodation state of at least one eye of the subject can be monitored using the autorefractometry or aberrometry unit. The results obtained can be used to control the procedure (e.g., to terminate or repeat individual steps in case of unwanted accommodation (e.g., exceeding a certain threshold)). The measurement can be performed continuously or only when detection is indicated.

[0315] Furthermore, an accommodation state (sphere, cylinder, low or high order aberrations) measured – ideally when signaling detectability – can be included in the calculation of sensitivity or refraction error. E. Blurring in the negative direction and incorporating a close-up measurement. Blurring in the negative direction.

[0316] In the above examples, the applied optical effect corresponds to a positive refractive error, since this cannot be compensated for by the subject through accommodation. However, the opposite approach is also possible, i.e., applying an optical effect that corresponds to a negative refractive error. The resulting accommodation can be managed as follows: - Ignoring accommodation; - Measuring subjects who, for example, have limited or poor accommodation due to physiological (e.g., age-related) or pharmacological (e.g., drops) conditions; - Measuring or monitoring the accommodation state; - Using assumptions about accommodation ability (e.g. depending on age according to the Duane curve, see Fig. 3).

[0317] The in Fig.The Duane curve shown in Figure 8 is taken from B. Lachenmayr, D. Friedburg, E. Hartmann, A. Buser: “Eye - Glasses - Refraction: Schober Course: Understand - Learn - Apply”, 2005, Fig. 1.29, and was originally published in Alexander Duane: “Studies in monocular and binocolar accommodation with their clinical applications”, Transactions of the American Ophthalmological Society, Vol. 20, 1922, pp. 132-157, PMID 16692582, PMC 1318318. The Duane curve shows that the human eye's ability to accommodate (accommodation range) decreases continuously from an average of 14 diopters to one diopter between the ages of eight and shortly after fifty.

[0318] The influence of accommodation on the sphere can be taken into account in the following ways, for example: - The amount of accommodation is subtracted from the amount of the distance of the applied effect from the refraction value for distance; - The refraction error is calculated directly from the applied effect and the measured or assumed refraction value.

[0319] Similarly, the astigmatic deviation can also be calculated using known formalisms (e.g., cross-cylinder formula, power vector notation) via the measured cylinder to account for changes in astigmatism due to accommodation. Furthermore, measured higher-order aberrations can be considered using known metrics. Incorporating a close-up measurement

[0320] The procedure described above can be combined with a determination of the objective near refraction values, the maximum accommodation, and / or the aberrations (lower or higher orders).

[0321] The procedure can be performed as follows: The eye's accommodation state is monitored using (ideally concurrent and as frequent as possible) autorefractometric or aberrometric measurements. An applied optical effect is used initially, allowing the recognition of the directional feature of the fitted optotype of the target. This can be an objective, subjective, or combined refractive value. In step 5) and, if necessary, step 6), the applied optical effect is then moved away from this optical effect in the positive direction. In step 4) and, if necessary, step 7), the subject signals the point at which they can no longer recognize the directional feature of the fitted optotype. If the applied effects are determined for two visual acuity levels, the applied effects for the higher visual acuity level can be determined first (steps 2-4) and then for the lower visual acuity level (steps 5-7).This allows the refractive error to be increased during the procedure, causing first the adjusted optotype with the more difficult recognition (higher visual acuity level) and then the one with easier recognition (lower visual acuity level) to become unrecognizable. The autorefractometric or aberrometric value measured when signaling the loss of recognition is used to calculate the sensitivity or visual acuity, respectively.

[0322] The value of the autorefractometric or aberrometric measurement, which corresponds to the greatest accommodation, is then used as the value (sphere, cylinder, low or high order aberration) for near refraction or for the maximum accommodative ability. F. Monitoring of pupil size

[0323] Furthermore, pupil size (e.g., pupil radius) can be monitored, for example, using a camera integrated into the autorefractometer or aberrometer, or using a separate camera. The pupil size measured at the point of blur or shortly before (e.g., up to 2 seconds before reaching the point of blur) can be used to determine the sensitivity to blur.

[0324] The measured pupil size can then be used to quantify the blurring of the image on the retina with the aid of a suitably parameterized eye model and the known additional fogging. For example, the angle at which the dispersion disk of a blurred point can be observed for a given pupil size and additional fogging can be calculated (see WO 2019 034525 A1). Within such a visual acuity model, the sensitivity can be determined as the decrease in visual acuity per unit angle of the dispersion disk. G. More complex models for sensitivity

[0325] In more complex models, a distinction can be made between the influence of spherical nebulae or refractive errors and astigmatic nebulae or refractive errors. For the same visual acuity level, spherical nebulae and astigmatic nebulae can be determined. I. Combination with other measurements

[0326] The present invention can be readily combined with or integrated into other measurements. In a preferred embodiment, the procedure according to Section A or B is performed after an autorefractometric or aberrometric distance measurement. This autorefractometric or aberrometric distance measurement already constitutes the first step according to Section A and does not need to be performed again. The procedure according to one of the above sections can be performed either before or after any near measurement. The former has the advantage that the (virtual) target is initially unknown to the subject, and the subject has already become familiar with the target for the near measurement. Reference symbol list V1 first preferred direction V2 second preferred direction

Claims

[1] Method for determining visual acuity characteristics of a subject who has at least one astigmatic refractive error, comprising the steps: - Providing refractive error data of the subject, wherein the refractive error data includes at least one axis position of a required optical cylinder correction; - Selecting a preferred direction (V1; V2) such that this preferred direction (V1; V2) either corresponds to the axis position assigned to the optical cylinder correction, or is rotated by 90° to this axis position, or the preferred direction (V1; V2) is derived from wavefront data using a point spreading function; - Creating a visual effect at least in the selected preferred direction; - Display of at least one adapted optotype which has a directional feature, wherein the adapted optotype is displayed oriented such that its directional feature is arranged parallel to the preferred direction (V1; V2); and - Determining the visual acuity characteristics of the subject for the selected preferred direction (V1; V2) taking into account at least one dimension of the directional feature of the adapted optotype as well as the applied optical effect; where a hatched area is used as the adapted optotype, in which the hatching lines are arranged perpendicular to the selected preferred direction (V1; V2); and / or in which, in addition to the adapted optotype, at least one further optotype is displayed, the gray value of which corresponds approximately to an average gray value of the adapted optotype, and the subject is asked to distinguish the displayed optotypes from each other as part of a visual task. [2] Method according to claim 1, wherein the directed feature of the adapted optotype has a sequence of light and dark areas which follow one another along the preferred direction (V1; V2). [3] Method according to claim 1 or 2, comprising the steps: - Providing an unadapted standard optotype with a directional feature; - Rotating the standard optotype in a display plane such that its directional feature is arranged parallel to the preferred direction (V1; V2); and - Displaying the distorted standard optotype as the adjusted optotype. [4] Method according to any one of the preceding claims, wherein: - as a first preferred direction (V1) the axis position is selected which is assigned to the optical cylinder correction and which is arranged in the first principal meridian of the required optical cylinder correction, wherein as the optical effect an optical sphere correction is applied which corrects the refractive error of the subject in the first principal meridian according to the refractive error data, and wherein as visual acuity characteristics the visual acuity of the subject for this first principal meridian is determined and / or - as a second preferred direction (V2) a direction rotated by 90° to the axis position is selected, which is arranged in the second principal meridian of the required optical cylinder correction, wherein as the optical effect an optical sphere correction is applied, which corrects the refractive error of the subject in the second principal meridian according to the refractive error data, and wherein as visual acuity characteristics the visual acuity of the subject for this second principal meridian is determined. [5] Method according to claim 4, wherein the visual acuity of the subject is determined for both the first and the second principal meridian of the required optical cylinder correction and a direction-independent visual acuity is derived from it. [6] Method according to one of the preceding claims, wherein a Landolt ring is used as the adapted optotype, the gap of which is displayed rotated by 90° to the selected preferred direction (V1; V2). [7] Method according to one of the preceding claims, wherein a Snellen-E is used as the adapted optotype, in which the connecting line linking the three parallel E lines is arranged parallel to the selected preferred direction (V1; V2). [8] Method according to claim 6 or 7, wherein the adapted optotype is displayed at least once rotated 90° clockwise relative to the preferred direction (V1; V2) and at least once rotated 90° counterclockwise relative to the preferred direction (V1; V2), and wherein the subject is asked to distinguish between these two differently rotated adapted optotypes as part of a visual task. [9] Method according to one of the preceding claims, wherein the applied optical effect is varied at least up to a limit refraction for the selected preferred direction, from which the subject recognizes the directional feature of the adapted optotype. [10] Method according to any one of claims 1 to 8, wherein the dimension of the directed feature of the adapted optotype is varied at least up to a limit dimension up to which the subject recognizes the directed feature of the adapted optotype. [11] Method according to one of the preceding claims, wherein at least one visual acuity and / or at least one sensitivity and / or at least one visual acuity-refraction value pair is determined as visual acuity characteristics. [12] Method according to one of the preceding claims, wherein the subject is presented with at least one visual task dependent on the displayed adapted visual sign, which the subject answers by providing active and / or passive feedback. [13] Method according to one of the preceding claims, wherein the visual acuity of the subject in the selected preferred direction (V1; V2) is determined under two different applied optical effects and a sensitivity of the subject is determined from this. [14] Method according to one of the preceding claims, wherein a subjective and / or objective refraction is performed and the refractive error data of the subject are derived from the refractive error of the subject determined therein. [15] Method according to one of the preceding claims, wherein the visual acuity characteristic of the subject is determined and converted into a different visual acuity type. [16] Using fitted optotypes, each having a directional feature arranged parallel to a preferred direction (V1; V2) which either corresponds to an axis position associated with an optical cylinder correction required by a subject, or which is rotated by 90° to that axis position, or the preferred direction (V1; V2) is derived from wavefront data using a point spreading function, to determine the subject's visual acuity characteristics for the selected preferred direction (V1; V2) taking into account at least one dimension of the directional feature of the fitted optotype; wherein - a hatched area is used as the adapted optotype, in which the hatching lines are arranged perpendicular to the selected preferred direction (V1; V2); and / or - in addition to the adapted optotype, at least one further optotype is displayed, the gray value of which corresponds approximately to an average gray value of the adapted optotype, and the subject is asked to distinguish between the displayed optotypes as part of a visual task. [17] Device for determining visual acuity characteristics of a subject who has at least one astigmatic refractive error, comprising: - a selection module which selects a preferred direction, wherein this preferred direction (V1; V2) either corresponds to an axis position which is assigned to an optical cylinder correction required by the subject, or is rotated by 90° to this axis position, or the preferred direction (V1; V2) is derived from wavefront data using a point spreading function; - a refraction unit configured to apply an optical effect to the subject in the selected preferred direction; - a display module with a display which shows at least one adapted optotype with a directional feature on the display such that the directional feature of the adapted optotype is arranged parallel to the preferred direction (V1; V2); and - a visual acuity characteristic determination module that determines the subject's visual acuity characteristics for the selected preferred direction (V1; V2), taking into account at least one dimension of the directional feature of the adapted optotype and the applied optical effect; wherein the display module is configured accordingly: - to display a hatched area as an adapted visual acuity symbol, in which the hatching lines are arranged perpendicular to the selected preferred direction (V1; V2); and / or - to display at least one additional optotype in addition to the adapted optotype, the gray value of which corresponds approximately to an average gray value of the adapted optotype, and the subject is asked to distinguish between the displayed optotypes as part of a visual task. [18] Device according to claim 17 comprising an eye tracking unit which tracks at least one eye of the subject when displaying the at least one adapted optotype.

Images