Method and optical device for determining visual acuity characteristics and / or refractive characteristics of a subject

Abstract

Method for determining visual acuity characteristics and / or refractive characteristics of a subject with a refractive error by means of an optical device (10) for displaying optotypes, which has a beam path through which the optotypes are displayed to the subject, wherein the optical device in the beam path has a target optic configured to image the optotype onto an entrance pupil of the subject, comprising the steps of: - providing effective aberration data of the imaging of an optotype through the beam path of the optical device (10) and through at least one refractive eye (20) onto the corresponding retina of the subject, wherein the effective aberration data include a combination of ocular aberration data of the at least one refractive eye of the subject with device aberration data of the optical device along the beam path of the device;- Selecting a preferred direction (V1; V2) depending on the effective aberration data, in particular based on effective wavefront data belonging to the effective aberration data; - Applying an optical effect at least in the selected preferred direction; - Displaying at least one fitted optotype having a directional feature, wherein the fitted optotype is displayed oriented so that its directional feature is parallel to the preferred direction (V1; V2); and - Determining the visual acuity characteristics and / or refractive characteristics of the subject for the selected preferred direction (V1; V2), taking into account at least one dimension of the directional feature of the fitted optotype and the applied optical effect.

Description

[0001] The invention relates to a method and an optical device for determining visual acuity characteristics and / or refraction characteristics of a subject.

[0002] Determining visual acuity as the visual acuity characteristic of a subject with a refractive error, especially an astigmatic refractive error, is a central task in optometry. A subject's astigmatic refractive error can be compensated by providing and / or applying an optical cylinder correction in addition to any optical sphere correction that may be required.

[0003] Known methods for determining the visual acuity of a subject with astigmatic refractive error are often time-consuming, labor-intensive, and / or error-prone, as they often rely on active feedback from the subject. Furthermore, determining visual acuity requires compensating for the subject's astigmatic refractive error by providing an optical cylinder correction and an optical sphere correction, for example, using a phoropter or trial glasses.

[0004] Holding the optical cylinder correction in front of the trial glasses or the phoropter is cumbersome and requires space, which is why the trial glasses or the phoropter can only be combined with other devices such as an eye tracker with difficulty.

[0005] Without providing the test subject with the required cylinder correction in the optical unit used, the astigmatic refractive error will not be compensated.

[0006] Therefore, often no or only a distorted visual acuity can be determined in the relevant area of ​​the subject, especially if the subject has a significant cylinder error.

[0007] The subsequently published document DE 10 2022 209 490 describes a method in which the visual acuity characteristics of subjects with astigmatic refractive error can be determined using adapted optotypes. The subject's refractive error data are taken into account to select a preferred direction, and at least one adapted optotype with a directional feature parallel to the preferred direction is displayed to the subject. This allows the subject's astigmatic refractive error to be reduced and / or compensated without the use of optical cylinder correction.

[0008] Unwanted optical aberrations can occur not only in the test subject, but also in devices with inferior or incorrectly aligned optical components, e.g., in optical devices with at least one tilted lens in the beam path, also known as the target beam path. Optical aberrations can also occur for other reasons, e.g., if the optical device is designed for more than just a display and therefore contains additional optical components that negatively impact the image quality in the beam path. Such optical components can be, for example, beam splitters arranged at positions where the light emitted by a target is not collimated.

[0009] The invention is based on the object of determining visual acuity characteristics and / or refraction characteristics simply and reliably using an optical device for displaying optotypes, in particular when the optical device itself has an optical aberration.

[0010] This object is achieved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims.

[0011] One aspect relates to a method, in particular a (fully) automatically performed method, for determining visual acuity characteristics and / or refraction characteristics of a subject having a visual impairment, by means of an optical device for displaying optotypes, which device has a beam path through which the optotypes are displayed to the subject. In this case, effective aberration data of the image of an optotype through the beam path of the optical device and through at least one ametropia-impaired eye onto the associated retina of the subject are provided, wherein the effective aberration data include a combination of eye aberration data of the at least one ametropia-impaired eye of the subject with device aberration data of the optical device along the beam path of the device.A preferred direction is selected depending on the effective aberration data, in particular based on effective wavefront data associated with the effective aberration data. An optical power is applied at least in the selected preferred direction. At least one adjusted optotype having a directional feature is displayed, wherein the adjusted optotype is displayed aligned such that the directional feature is arranged parallel to the preferred direction. Finally, the subject's visual acuity characteristics and / or refraction characteristics are determined for the selected preferred direction, taking into account at least one dimension of the directional feature of the adjusted optotype and the applied optical power.

[0012] The term "effective" in "effective aberration", "effective wavefront", etc. is used in this document to always refer to a composite optical system comprising both the optical device and at least one eye of the subject and / or taking into account the respective associated aberrations.

[0013] The subject's visual acuity and / or refractive characteristics can be determined for one eye, for both eyes individually (i.e., monocular), or for both eyes together (i.e., binocular). Preferably, the visual acuity and / or refractive characteristics are determined monocularly for each eye of the subject individually.

[0014] In the method, at least one optotype is displayed to the subject by means of the optical device. The optical device can comprise a light field display and / or a display and / or a refraction unit and / or a phoropter for displaying the optotype. The respectively displayed optotype is projected onto the subject's entrance pupil by the beam path of the optical device. The optical device can comprise an optical system in the beam path that can be configured to project the image of the optotype (e.g., as predetermined) onto the subject's entrance pupil. This optical system is also called a target optical system.

[0015] The subject has a visual impairment, which may include astigmatic refractive error. The subject's visual impairment corresponds to an ocular aberration of the subject. Furthermore, the optical device may also exhibit an imaging error when displaying the optotype through the optical path, which corresponds to a device aberration. The device aberration may also include an astigmatic imaging error.

[0016] Device aberrations can be caused by inferior and / or incorrectly aligned optical components of the optical device. For example, a tilted lens may be positioned in the optical path. Optical aberrations can also be caused by additional optical components in the optical path, such as beam splitters, which are positioned at positions where the light used to display the optotype is not collimated. The entire set of optical components in the optical path can be referred to as the optics of the optical device's optical path, specifically the target optics.

[0017] In general, a target can be generated by a display of the optical device, which is projected into the subject's pupil by the beam path and / or the target optics. The displayed optotypes can be used as the target, in particular the adjusted optotype. Alternatively, a point light source and / or another image can be displayed as the target.

[0018] The ocular aberration and the device aberration together result in the actual aberration occurring when displaying an optotype through the optical path of the optical device, the so-called effective aberration. The ocular aberration can be described by the ocular aberration data, the device aberration by the device aberration data, and the effective aberration by the effective aberration data.

[0019] The resulting effective aberration may exhibit effective astigmatism and / or coma, which is corrected and / or reduced during conventional refraction using optical cylinder correction. The astigmatism may be present either in the subject or in the optical device, or in both, and may result from a superposition of the aberrations.

[0020] People with astigmatic refractive error often require additional optical sphere correction, which is combined with optical cylinder correction. These optical corrections can be integrated into a spectacle lens, a contact lens, and / or an intraocular lens for the patient.

[0021] The applied optical effect can be achieved by placing an optical correction device (such as a lens) in front of the subject's respective eye. The optical correction manipulates the light entering the subject's eye. Thus, the optical corrections can correspond to a given optical effect, in particular an optical effect with a spherical and / or cylindrical optical effect.

[0022] To select the preferred direction, the effective aberration data is first required. The effective aberration data includes the ocular aberration data, which may have been determined, for example, during a subjective and / or objective refraction. The ocular aberration data may be available as prescription data for the subject. The method for determining visual acuity characteristics and / or refractive characteristics can be integrated into and / or performed after an objective and / or subjective refraction determination.

[0023] In addition, the effective aberration data includes the device aberration data. The device aberration data can be measured, for example, using a wavefront sensor and / or provided as effective wavefront data.

[0024] For the method, knowledge of the device aberration data and / or ocular aberration data per se is not absolutely necessary, as long as the effective aberration data is acquired, which contains the device aberration data and ocular aberration data in some way. However, the method can preferably comprise determining a device-specific device aberration, in particular, which is particularly preferably stored. The storage can take place in a database independent of the device and / or in a memory of the device and / or an external storage medium. The (device-specific) device aberration can, for example, be determined in advance as a result of a calibration protocol, for example in the factory or during commissioning, and then stored.However, it is understood that the device aberration does not need to be determined separately, and the method also works using the effective aberration data.

[0025] The effective aberration data can include at least one axis position of an effectively required optical cylindrical correction. Furthermore, the effective aberration data can also include the strength of the effectively required optical cylindrical correction. The effective aberration data can also include an effectively required optical sphere correction, the effectively required optical cylindrical correction, and / or the axis position of the cylinder associated with the cylindrical correction.

[0026] Alternatively, or in this case, the effective aberration data may be based on an effective wavefront analysis and be based on effective wavefront data thus determined.

[0027] The preferred direction is selected based on the effective aberration data, in particular on the resulting and thus assigned effective axis position of a required cylindrical correction. The preferred direction can be, for example, the effective axis position of the effective aberration directly, or a direction rotated by 90° to this effective axis position.

[0028] If the effective aberration data is based on effective wavefront data, the preferred direction can also be derived from this effective wavefront data using a point spread function. The preferred direction can be derived from a point spread function calculated based on the effective wavefront data. Here, the preferred direction can be selected, for example, as the direction and / or axis of the smallest extension of the point spread function. The direction of least confusion can be selected, for example, as the direction of the smallest standard deviation of the point spread function.

[0029] The effective axis position of the effective aberration can be arranged in a plane that is approximately perpendicular to a selected direction of gaze of the test subject. For example, a direction of gaze of the test subject in the position of use can be selected as the direction of gaze, which is defined in the relevant standards. The effective axis position can be arranged and / or defined in a plane that is approximately perpendicular to the position of use. In this case, the effective axis position can in particular be arranged in a plane in which a spectacle lens and / or a contact lens of the test subject is to be arranged. The effective axis position can therefore in particular coincide with an axis of an optical cylindrical correction that is to be integrated into a spectacle lens and / or a contact lens for the test subject.

[0030] The preferred direction can be arranged approximately in the first principal section of the effectively required optical cylinder correction and additionally approximately perpendicular to the subject's line of sight.

[0031] If a direction rotated by 90° relative to the effective axis position is selected as the preferred direction, the rotation of 90° occurs within a plane approximately perpendicular to the subject's line of sight. The selected preferred direction can be positioned approximately in the second principal section of the effectively required optical cylindrical correction and also approximately perpendicular to the subject's line of sight.

[0032] After a preferred direction has been selected as described based on the effective aberration data, the optical effect is applied at least in the selected preferred direction. For this purpose, a rotationally symmetric optical lens, such as an optical sphere correction, can be provided. In particular, the optical sphere correction can be applied that, based on the effective aberration data, at least partially corrects the subject's refractive error in the selected preferred direction.

[0033] If the effective axis position of the effectively required optical cylinder correction is selected as the preferred direction, i.e. the first principal section of the cylinder correction, then an optical sphere correction of the strength can be used as the optical effect, which corresponds exactly to the effectively required sphere correction resulting from the effective aberration data, without taking the effective cylinder error into account.

[0034] If the preferred direction is selected as the direction rotated by 90° to the effective axial position, i.e., the second principal section through the effectively required cylindrical correction, the optical effect can be, for example, an optical spherical correction with a strength that results from the sum of the effectively required spherical correction from the effective aberration data plus the resulting effectively resulting cylindrical correction (e.g., both given in diopters). When calculating the sum, the signs of the required effective spherical correction and the required effective cylindrical correction must be taken into account.

[0035] If the effective aberration data result in a required effective spherical correction of s and a required effective cylindrical correction of z (sometimes abbreviated as c), a correction with the value s can be applied as the optical power for the first principal section, and one with the value s+z for the second principal section.

[0036] The optical effect can be applied by holding the said optical effect in front of at least one eye of the subject. This can be achieved, for example, by physically holding the respective optical lens in front of the subject, e.g., using trial glasses and / or a refraction unit, which can be designed, for example, as a component of the optical device. In an alternative approach, the optical effect is not applied physically, but can be simulated as part of a wavefront simulation. The exact method of application can therefore depend on the refraction unit used.

[0037] To achieve the optical effect at least in the selected preferred direction, an optical spherical effect is preferably used, for example, a rotationally symmetric lens. This produces the desired optical effect not only in the selected preferred direction, but also throughout the entire sphere. An optical spherical effect can also be simulated in the virtual realm.

[0038] With the optical effect thus applied, the effective aberration can be at least partially corrected for the selected preferred direction.

[0039] It is noteworthy that no optical cylindrical correction is required to determine the visual acuity characteristics and / or refractive characteristics. It is sufficient to determine the visual acuity characteristics and / or refractive characteristics according to the methods by applying and / or maintaining a purely optical sphere correction, for example, without requiring an optical cylindrical correction.

[0040] Applying an optical sphere correction as the optical power is usually easier to implement than applying an optical cylinder correction, for example, because the sphere correction does not require consideration of the axial position. Thus, the procedure is simplified by eliminating the need for optical cylinder corrections.

[0041] The visual acuity characteristics can be determined, for example, as at least one visual acuity for the applied optical power, and / or a sensitivity of the subject, and / or a visual acuity-correction tuple pair. The refraction characteristics can be determined, for example, as at least one visual acuity-correction tuple pair and / or at least one refraction value. A visual acuity-correction tuple pair contains information about the visual acuity of the subject if the associated correction is applied as an optical power for at least the selected preferred direction. In this respect, the visual acuity-correction tuple pair can also contain the associated preferred direction. This tuple pair can, for example, be designed as a value pair. The tuple pair can, for example, contain the visual acuity in 20 / 10 notation and / or the correction can also consist of more than just a single value. In other words, the visual acuity and / or the correction can be stored as a tuple in the visual acuity-correction tuple pair.

[0042] Visual acuity determination based on optotypes, such as optotypes, is generally known. However, the invention uses not (only) normal and unadapted standard optotypes, but rather adapted optotypes that are adapted to the selected preferred direction and thus to the effective aberration of the subject and the optical device. Optotypes that exhibit a directional feature are suitable for this purpose.

[0043] The adjusted optotype has a feature with a specific orientation, which is the directional feature that the subject is supposed to recognize during a visual task. Optotypes with directional features are generally known, such as Landolt rings or the Snellen E scale. However, Landolt rings, for example, are standardly aligned so that the gap of the respective Landolt ring is located at exactly 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°.

[0044] Deviating from the generally accepted arrangement of the gap between the Landolt rings as optotypes, adapted optotypes are now used whose directional feature is arranged exactly and / or as exactly as possible parallel to the selected preferred direction. If the effective axial position assigned to the required optical cylindrical correction is, for example, exactly 12°, or generally exactly the angle α, and this effective axial position is selected as the preferred direction, the adapted optotype is arranged so that its directional feature is displayed exactly at the angle 12°, generally at the angle α. The display can be achieved using the optical device. The optotype is thus precisely adapted to the selected preferred direction, for which the applied optical sphere correction effectively corrects the effective aberration, including the subject's ametropia.

[0045] The arrangement of the directional feature of the adjusted optotype in the preferred direction enables the test subject to recognize this feature of the adjusted optotype even if it is not fully corrected, i.e., not also cylindrically corrected. Even if the test subject cannot see the adjusted optotype completely clearly because the effective astigmatism is not corrected by optical cylindrical correction, they can still at least recognize the directional feature if their visual acuity is sufficiently good. Thus, the adjusted optotype enables the test subject to recognize at least the directional feature of the adjusted optotype if they are optimally and / or at least sufficiently effectively corrected in the preferred direction by the applied optical power.

[0046] Finally, the subject's visual acuity and / or visual acuity characteristics for the selected preferred direction can be determined, taking into account at least one dimension of the directional feature of the adjusted optotype. The determination of the visual acuity and / or the desired characteristics can be performed in the usual way, i.e., depending on the dimension of the directional feature that the subject can just barely perceive and / or identify with the applied optical power.

[0047] To determine the dimension required for calculating visual acuity, the subject can be shown several adjusted optotypes sequentially and / or simultaneously that differ in one dimension of the directed feature. The subject can be asked to identify at least one adjusted optotype as part of at least one visual task.

[0048] Within the context of the visual task and / or a sequence of visual tasks, at least one adapted optotype can be displayed in progressively smaller sizes, making the visual tasks progressively more difficult. Alternatively, the differently sized adapted optotypes can also be displayed simultaneously. This allows the determination of the maximum size of the directional feature the subject can still recognize the adapted optotype.

[0049] The subject's effective aberration data, in combination with the device required for the procedure, may, for example, correspond to the best correction and / or the best refraction required by the subject to correct the effective aberration. Additionally or alternatively, the effective aberration data may also deviate slightly from the best optical corrections required. For example, ocular aberration data may only correspond to the effective aberration data determined for the subject based on an objective refraction measurement. The objectively determined refraction data usually correspond very precisely to the axial position of the cylindrical correction actually required by the subject, at least in the axial position determined in this way.

[0050] In addition to the best correction, a slightly "blurred" (i.e., modified) optical correction can also be applied as an optical effect, for example, when determining the subject's sensitivity. Intentionally "degraded" effective aberration data can thus also be used.

[0051] In one variant, the applied optical power can be completely independent of the effective aberration data. Here, the dimension of the directional feature of the displayed adjusted optotype can be kept constant, and instead, the applied optical power can be varied for this constant dimension until the subject can (or can no longer) recognize the directional feature of the adjusted optotype. In this way, a visual acuity-correction tuple pair can be determined that can be independent of the (subjectively and / or objectively and / or effectively determined) optimal effective correction.

[0052] In principle, however, a visual acuity determination as visual acuity characteristics for the selected preferred direction can be determined most accurately if the optimal optical correction that the subject effectively needs with the optical device in the selected preferred direction is used as the optical effect.

[0053] The method makes it possible to determine the subject's visual acuity and / or refractive characteristics, such as visual acuity, without requiring the subject to have and / or apply optical cylinder corrections. Instead, the adjusted optotypes are used, which, for example, are precisely adjusted to the axial position of the actually required cylinder correction, thus making the application of optical cylinder corrections unnecessary. This makes it possible to determine the visual acuity and / or refractive characteristics using, for example, a less expensive optical device that cannot itself apply optical cylinder correction.

[0054] Furthermore, the method allows the refraction unit used to be combined with additional instruments, as more space is available for additional instruments if the option of applying the required cylinder correction can be omitted. For example, a refractometer, particularly an autorefractometer, can be used as the refraction unit to apply the optical power.

[0055] In a visual acuity measurement, the effective aberration can only be corrected for the selected preferred direction, but not for the perpendicular principal section of the required cylinder correction.

[0056] As adjusted optotypes, optotypes can be used whose lowest spatial frequencies lie in the direction of the most uncorrected principal section, i.e., are aligned parallel to it. Alternatively or additionally, the highest spatial frequencies of the optotypes used can lie in the direction of the most corrected principal section, i.e., are aligned parallel to it.

[0057] The method makes it possible to at least partially compensate for unwanted and / or only difficult and / or disproportionately expensive disadvantages of the unwanted optical aberrations of the optical device by an optimized alignment of the adapted optotypes, so that a determination of visual acuity is possible despite the additional aberrations of the optical device.

[0058] By combining the unwanted aberration of the optical device, for example, with aberrations of the eye that cannot be corrected by the optical device, and aligning the adjusted optotypes to be displayed by the optical device according to the preferred direction resulting from the combined effective aberration, the effect of unwanted directional optical aberrations can be reduced and / or avoided. This applies in particular to astigmatic aberration and / or other unwanted aberrations such as astigmatism or coma that may be present in the optical path of the optical device.

[0059] The method can be carried out at least partially automatically, i.e., individual steps of the method can be carried out, for example, by means of software support and / or computer-implemented. In particular, at least one or all of the following steps of the method according to the first aspect can be computer-implemented: • The effective aberration data may be provided on a computer system, in particular in a storage medium. • The preferred direction can be determined automatically by a computer system, e.g. by computer-assisted evaluation of the effective aberration data and / or the associated effective wavefront data. • The application of the optical effect in at least the selected preferred direction can be carried out at least computer-assisted, e.g. by means of a computer-generated control signal which is sent to a light field display and / or a phoropter. • The display of the at least one adapted optotype with the directed feature, in particular on a display and / or a light field display, can also be computer-controlled. • The determination of the subject’s visual acuity characteristics and / or refraction characteristics for the selected preferred direction can also be carried out using software and thus computer-implemented.

[0060] In addition, at least some of the optional method steps described below can be computer-implemented and / or computer-assisted and / or fully or partially automated.

[0061] According to one embodiment, the effective aberration data includes an astigmatism of the at least one ametropia-affected eye and / or the optical device. This can result in an effective astigmatism of the combined optical system, optical device, and eye, and from this, for example, an effectively required cylinder correction with an associated effective axial position. Astigmatic aberrations can be particularly advantageously compensated and / or reduced with adapted optotypes.

[0062] According to one embodiment, the device aberration data of the optical device depend on and / or comprise a function of a target proximity, wherein the target proximity corresponds to a mean curvature of a wavefront propagating along the beam path of the optical device, in particular in a pupil plane of the at least one ametropia-impaired eye. Thus, the unwanted device aberrations can depend on the set proximity of a target. The target can be an optotype displayed by the optical device, in particular the at least one adjusted optotype. The target can be displayed on a display such as a screen of the optical device and imaged into the subject's eye through the beam path. For example, the magnitude and / or angle of the unwanted astigmatism of the optical device can change as a function of the proximity of the target.

[0063] Target proximity is understood to be the mean curvature of the wavefront propagating along the beam path of the optical device, in particular in the pupil plane or in the plane in the beam path at which, for example, glasses to be manufactured for the subject are to be arranged in a usage position. The wavefront can be generated by an image point of the target, i.e. by a point light source. Target proximity represents an adjustable device parameter of the optical device and can be changed and / or adjusted, for example, by changing the position of optical components, such as lenses, of the optical device and / or the target. This change and / or adjustment can be described using the target proximity function. Taking the target proximity function into account makes it easier to consider and / or adjust the device aberration and / or the device aberration data.

[0064] According to one embodiment, the device aberration data of the optical device depend on and / or include a pupil size of the at least one ametropia-impaired eye. Thus, the unwanted device aberrations effectively present and / or evaluated at the location of the entrance pupil of the subject's eye can depend on the subject's pupil size. In particular, in the presence of second-order astigmatism, the magnitude of the astigmatism of the optical device and / or its angle can depend on the pupil size. Taking the pupil size into account makes it easier to detect and / or adjust the device aberration and / or the device aberration data.

[0065] According to one embodiment, the device aberration data of the optical device are acquired as fixed device parameters of the optical device and / or as a function of adjustable device parameters of the optical device. The device aberrations can be acquired both with fixed device parameters and with variable device parameters of the optical device, e.g., with a fixed target proximity and with a variable target proximity. With variable device parameters, the device aberrations can be acquired taking into account a function of the target proximity.

[0066] In any case, the device parameters can be captured using at least one device model. To capture the device model, the optical imaging properties of the optical device can be simulated using ray computation applications such as ZEMAX. Alternatively, a device model can be tailored to the individual optical device and generated empirically from measurements at different target proximities and / or pupil sizes. If the effect of individual, even combined, optical components of the optical device is known, this information can be incorporated into the device model.

[0067] Dependencies of the device parameters on the target proximity and / or pupil size within the device model can be and / or become quantified, in particular in the device model.

[0068] According to one embodiment, the device aberration data of the optical device are measured using a wavefront sensor. For example, measurements from the wavefront sensor can be used to record the device aberration data and / or the device parameters. The wavefront sensor can measure the wavefront generated by a point light source located in the plane of the target through the imaging optics in the beam path of the optical device, i.e. the target optics, at the expected position of the entrance pupil. The point light source can be, for example, a luminous pixel or a group of luminous pixels of a microdisplay used to display the optotypes, or the diffuse scattered light of a focal point of a laser beam generated at the position of the target. Measurement using a wavefront sensor is relatively easy to perform and / or can deliver very accurate results.

[0069] The device model can be generated from such wavefront sensor measurements by fitting the Zernike coefficients corresponding to a pupil radius r0 with a polynomial of the target proximity, e.g., a linear or quadratic function of the proximity. For evaluation, the wavefront modeled in this way can be scaled in Zernike representation to the subject's pupil radius r0. Further details on determining the device models are provided below.

[0070] According to one embodiment, when selecting the preferred direction, the effective aberration data are used as the effective wavefront W eff taken into account, where: Weff=WF−WT(AT).

[0071] Here W F the wavefront of the refractive error of at least one eye of the subject and W T (A T ) which is determined by a target proximity A Tdependent wavefront of a device aberration of the optical device along the optical path of the optical device.

[0072] Equation (1) expresses a combination of the eye aberration and the device aberration mathematically as a sum. The wavefronts W F and W T refer to a common plane. If the ocular aberration, as is often the case, occurs in a plane fixed to the eye, preferably in the plane of the entrance pupil, W F be appropriately converted to this same level.

[0073] The aberrations effectively present when viewing the target are defined as the effective wavefront W eff The wavefront W FThe visual impairment of at least one eye of the subject concerns a wavefront entering the eye, which creates a focal point on the retina at the location of sharpest vision. The target proximity A T dependent wavefront W T (A T ) can be defined in the pupil plane at the location of the entrance pupil of the eye.

[0074] The preferred direction to which the adjusted optotype is aligned can be defined as the direction of the smallest extension of the effective wavefront W effcalculated point transfer function. The optotypes adjusted according to this preferred direction are generally better recognizable by the subject because their higher-frequency details are better transmitted through the composite optical system (consisting of the beam path of the optical device, in particular the target optics, and the subject's eye) when oriented in the preferred direction selected in this way than in other orientations, e.g., perpendicular to the preferred direction.

[0075] When considering the wavefront in second order, the cylinder axis of the effective wavefront W eff be used as the preferred direction.

[0076] When using adjustable device parameters, the target proximity and / or its function can be selected such that the point transfer function is minimized as a function of the target proximity and direction, i.e., a direction in the retinal plane. The target proximity and / or its function can be used as the setting condition for the adjustable device parameters. A numerical method can be used to set this setting condition.

[0077] The wavefronts can also be considered approximately in second order, e.g., as a quadratic function of the pupil coordinates. The setting condition, i.e., that the point transfer function is minimal as a function of target proximity and direction, can in this case be equivalent to at least one of the principal sections of the effective wavefront W eff is planar, and / or that the curvature matrix of W effhas at least one eigenvalue of 0. The preferred direction for the adjusted optotypes can be determined from the direction of the plano principal section of W eff and / or from the direction of the eigenvector of the curvature matrix of W eff to the eigenvalue of 0.

[0078] According to one embodiment, at least a first and / or second principal section of an effective wavefront of the effective aberration data is selected as the first and / or second preferred direction and / or a direction in which a curvature matrix of the effective wavefront of the effective aberration data has an eigenvalue of 0, in particular by means of the matrix equation: det(Weff(AT))=det(WF−WT(AT))=0.

[0079] Where W eff (A T ) the effective wavefront of the effective aberration data, W F the wavefront of the refractive error of at least one eye of the subject and W T (AT ) which is determined by a target proximity A T dependent wavefront of a device aberration of the optical device along the beam path of the optical device. For reasons of simplicity, equation (2) can preferably be approximated by relating it to the same wavefront data as equation (1), i.e., to wavefronts with the same reference plane as for equation (1), which there is preferably the entrance pupil of the eye. This approximation can preferably be dispensed with, and the vectors can be calculated in the actual display plane, which are then mapped onto vectors in the image plane or onto the zero vector. Here, too, a determinant equation is used, similar to equation (2), but based on transformed matrices, so that the anamorphic distortion introduced by the target optics between the display plane and the reference plane of the wavefronts from equation (1) is subtracted.

[0080] When determining the setting condition, the target proximities can be determined first. Usually, two target proximities result for the setting condition, except when the effective wavefront W eff is a plane wavefront, resulting in infinitely many solutions for the direction. The necessary device parameters of the setting condition are thus determined by searching for the zeros of the determinant of the curvature matrix as a function of the target proximity, e.g., numerically. Thus, the solutions A (T,1) and A (T,2) the matrix equation (2) listed above.

[0081] Afterwards, an eigenvalue decomposition of the found target proximities A (T,1) and A (T,2) associated curvature matrices of the effective wavefront W effThe eigenvectors with eigenvalue 0 correspond to the preferred direction along which the adjusted optotypes are aligned with their higher spatial frequencies.

[0082] The calculation of the target proximity and the preferred direction can also be done in other representations which are analogous to the curvature matrix of second-order wavefronts, e.g. in the power vector representation.

[0083] Instead of the target proximity, another device parameter can be used which significantly influences the target proximity, e.g. positions or distances of the lenses of the target optics and / or the position of the target.

[0084] The calculations carried out above mainly at the position of the entrance pupil of the subjects' eyes can be carried out analogously at other positions, e.g. in the vertex plane of a spectacle lens.

[0085] In a further development, an axial position located in the first principal section of the effective wavefront of the effective aberration data can be selected as a first preferred direction, and an optical sphere correction can be applied as the optical effect, which, according to the effective aberration data, corrects the ametropia of the subject and / or the optical device in the first principal section of the effective wavefront of the effective aberration data. The subject's visual acuity for this first principal section can be determined as the visual acuity characteristics.

[0086] Alternatively or additionally, an axial position located in the second principal section of the effective wavefront of the effective aberration data can be selected as a second preferred direction, and an optical sphere correction can be applied as the optical power, which, according to the effective aberration data, corrects the refractive error of the subject and / or the optical device in the second principal section of the effective wavefront of the effective aberration data. The subject's visual acuity for this second principal section can be determined as the visual acuity characteristics.

[0087] In this way, visual acuity can be determined using the optical device without the subject having to undergo cylinder correction.

[0088] The subject's visual acuity can be determined for the first and second principal section, which corresponds to the effective wavefront of the effective aberration data. From this, a direction-independent visual acuity can be derived. In other words, the first preferred direction is selected, and the subject's visual acuity for the first principal section is determined, and the second preferred direction is selected, and the subject's visual acuity for the second principal section is determined. As a result of the visual acuity determination, the result for each principal section can initially be given. In addition, a direction-independent visual acuity can be derived from these two visual acuity values. The direction-independent visual acuity can, for example,be expressed as the highest value determined during 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 ones of the above values.

[0089] In one embodiment, visual acuity is determined for only one of the two principal sections. In this case, an excellent principal section is selected. The excellent principal section can be the principal section for which the required optical correction is more pronounced in the plus direction, or more pronounced in the minus direction, or for which a stronger correction is required in terms of magnitude, or for which a weaker correction is required in terms of magnitude. The principal section whose axis position is closer to the vertical or the principal section whose axis position is closer to the horizontal can also be selected.

[0090] In general, visual acuity can be understood as detectability as a function of size, but also as detectability as a function of other parameters that influence the display, such as contrast. Visual acuity can also be used as a combination of detectability as a function of size and detectability of contrast and / or other of these parameters.

[0091] According to one embodiment, the directional feature of the adjusted 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 aligned perpendicular to the lines of a hatching, or perpendicular to the arrangement of the gap of a Landolt ring. Thus, perpendicular to the gap of a Landolt ring, the dark edge of the circle is first followed by the light gap and then again by the dark edge of the circle. Thus, the directional feature of a Landolt ring is arranged perpendicular to the gap. In a Snellen E, the directional feature is arranged perpendicular to the three parallel E lines. In general, the directional feature can correspond to a sequence of at least one light area following 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 aligned perpendicular to the preferred direction.

[0092] 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 arranged parallel to the preferred direction. Finally, the thus rotated standard optotype is displayed as the adapted optotype. The display can take place in particular on a screen of the optical device within a display plane. In this case, the unadapted standard optotype can initially be used as the starting point, which is rotated (e.g. purely mathematically, without being displayed) so that it is arranged correctly aligned with the selected preferred direction. In this way, the unadapted standard optotype is converted 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 should be used. The display plane is preferably positioned approximately perpendicular to the subject's line of sight and / or approximately parallel to the selected preferred direction.

[0093] By using an initially unadapted standard optotype with a directional feature, the adapted optotype can be easily created from this unadapted standard optotype by simply rotating it, e.g., around the center of the standard optotype and / or around another point in the display plane. This adapted optotype can be adjusted to any axis position of the required optical cylinder correction. Furthermore, the adjusted optotype can be scaled as required on the display, so that the adjusted optotype can be represented and / or displayed larger or smaller, depending on the visual task currently presented to the subject.

[0094] In embodiments, at least one of the following optotypes may be used as the adjusted optotype: - a Landolt ring whose gap is displayed rotated by 90° to the selected preferred direction; and / or - a Snellen E in which the connecting line connecting the three parallel E lines is arranged parallel to the selected preferred direction; and / or - a hatched area in which the hatching lines are arranged perpendicular to the selected preferred direction.

[0095] Rotating the Landolt ring gap 90° relative to the selected preferred direction ensures that the dark-light-dark sequence across the Landolt ring gap is aligned exactly in the selected preferred direction. This means that the directional feature of the Landolt ring is aligned exactly parallel to the selected preferred direction, allowing visual acuity for the selected preferred direction to be easily determined.

[0096] The sequence of three parallel E lines can be used as a directional feature of this Snellen E. For example, the sequence: light (background), dark upper line, light space, dark middle line, light space, dark lower E line, and finally light background. This also allows for easy adaptation of the Snellen E as a standard optotype to the preferred direction and thus its use as an adapted optotype.

[0097] The adjusted optotype can be displayed at least once rotated 90° clockwise relative to the preferred direction and at least once counterclockwise relative to the preferred direction. The test subject can be asked to distinguish between these two different rotated adjusted optotypes as part of a visual task. For example, the test subject can be asked to distinguish whether the gap in the Langolt ring is directed to the left or to the right, provided the preferred direction is approximately vertically upwards. The same applies to the use of the Snellen E as an adjusted optotype.

[0098] A hatched area can be used as at least one of the adapted optotypes, in which the hatching lines are arranged perpendicular to the selected preferred direction. A figure, for example a circle, a rectangle, a symbol, an animal, letters or similar, can be used as the hatched area. The figure is filled with hatching. Preferably, the figure does not have any edge lines that could disrupt the hatching, but is simply designed as a hatched, filled figure without a border. 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 figure itself is as uniformly formed as possible and has few details, for example if it is designed as a circle or a square.Preferred are therefore figures that are as simple and detailed as possible. 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., with hard black and / or white edges, or it can be continuous. For example, the hatching with a continuous gradient can be designed with a sinusoidal intensity gradient or a similar intensity gradient.

[0099] According to one embodiment, in addition to the adjusted optotype, at least one further optotype is displayed, the gray value of which approximately corresponds to an averaged gray value of the adjusted optotype, and the test subject is asked to differentiate the displayed optotypes from one another as part of a visual task. Instead of an optotype with an averaged gray value, an optotype can also be used whose hatching is not perpendicular to the selected preferred direction like the adjusted optotype, but approximately parallel to the preferred direction. Such an optotype appears to the test subject as an essentially gray optotype perpendicular to the preferred direction due to their astigmatic refractive error, which is incorrectly corrected for this hatching orientation.For example, several such gray optotypes and one adapted optotype can be displayed on one display plane during a visual task, or conversely, several adapted optotypes and one such gray optotype. The test subject can be asked to identify the displayed optotype that differs from the others.

[0100] According to one embodiment, the applied optical power is varied at least up to a limiting refraction for the selected preferred direction, above which the test subject can recognize the directional feature of the adjusted optotype. The dimension of the displayed adjusted optotype can be kept constant. An extreme value of the refraction unit used, e.g. ±20 diopters, can be used as the starting value for the applied optical power. Alternatively, a diopter value can be used as the starting value which deviates by a predetermined deviation of e.g. ±5 diopters from the optical sphere correction actually required according to the effective aberration data. After the starting value has been applied, the applied optical power is varied, e.g. continuously or in fixed steps, until the test subject can recognize (or can no longer recognize) the directional feature of the adjusted optotype.The optical power currently applied when recognizing the directional feature of the adjusted optotype corresponds, as limiting refraction, to an optical correction, with which the subject has a visual acuity dependent on the dimension of the directional feature of the displayed adjusted optotype. Thus, a visual acuity-refraction tuple pair for the preferred direction is determined as visual acuity characteristics.

[0101] If this procedure is repeated with at least a second adjusted optotype in which the directed feature has different dimensions, a second visual acuity-refraction tuple pair can be determined that differs from the first determined visual acuity-refraction tuple pair. From these two different visual acuity-refraction tuple pairs, for example, the subject's sensitivity can be determined.

[0102] In an alternative embodiment, the dimension of the directional feature of the adapted optotype is varied at least up to a limiting dimension up to which the test subject can recognize the directional feature of the adapted optotype. In this case, the applied optical power can be kept constant. As an optical power, for example, an optical correction can be applied which corrects the test subject's refractive error in the selected preferred direction according to the effective aberration data. For example, an optimal optical correction can be used which has been determined as part of an objective and / or subjective refraction. In this alternative, the dimension of the directional feature of the adapted optotype can be varied and it can be checked up to which limiting dimension the test subject can still recognize the directional feature. From this limiting dimension, the visual acuity can be determined in the classic way.The dimension of the directional feature of the adjusted optotype can be varied by displaying differently sized adjusted optotypes and / or by varying the size of the displayed adjusted optotype(s). This can be done within the context of at least one visual task and / or a sequence of different visual tasks, with at least one adjusted optotype being displayed within the context of each visual task. Thus, the visual acuity with this applied optical power can be determined as a visual acuity characteristic for the selected preferred direction. A visual acuity-refraction tuple pair with the associated preferred direction can also be determined here.

[0103] If this procedure is repeated with at least a second optical power applied in the selected preferred direction, a second visual acuity-refraction tuple pair can be determined that differs from the first determined visual acuity-refraction tuple pair. From these two different visual acuity-refraction tuple pairs, for example, the subject's sensitivity can be determined.

[0104] In embodiments, at least one visual acuity and / or at least one sensitivity and / or at least one visual acuity-refraction tuple pair and / or at least one refraction value can be determined as visual acuity characteristics and / or refraction characteristics. In particular, a value related to the visual acuity can be determined, i.e., at least one visual acuity and / or at least one sensitivity and / or at least one visual acuity-refraction tuple pair.

[0105] Here, the sensitivity can be determined depending on a sensitivity metric, e.g., specifically for at least the selected preferred direction. In addition, a sensitivity for the second preferred direction can also be determined, e.g., a direction rotated by 90° to the first selected preferred direction. However, a direction-independent sensitivity can also be determined (alternatively or additionally). The direction-independent sensitivity can, for example, be determined from the two sensitivities for the first and second preferred direction, or on the basis of two direction-independent visual acuity-refraction tuples (where, for example, the associated direction-independent visual acuity has been determined as an average of the visual acuity values ​​for the two preferred directions), or on the basis of a capable sensitivity metric that can determine a direction-independent sensitivity from at least two direction-dependent visual acuity-refraction tuples.

[0106] According to one embodiment, the subject is presented with at least one visual task dependent on the displayed adjusted optotype, which the subject answers by providing active and / or passive feedback. One embodiment of active feedback can, for example, be the subject verbally answering a question from an optician and / or another examiner regarding a visual task. Active feedback can also be provided, for example, by pressing a button and / or a mouse, with a gesture, and / or with a gaze. The subject's gaze can be recorded, for example, using an eye-tracking unit.

[0107] Using such an eye tracking unit, a passive response, i.e. passive feedback, can also be given. In this way, the eye tracking unit can detect which optotype the test subject is currently fixating. This can determine whether the test subject is, for example, subconsciously fixating on an optotype that differs from the others because they have recognized it, or whether the test subject is unable to recognize the different optotype. In principle, visual tasks with passive and active response can be combined. Preferably, the response, i.e. the feedback, from the test subject is recorded without any intervention from an examiner. In this way, the test subject can either actively enter the feedback themselves, for example using a button and / or a mouse-like control, or it can be recorded passively.Eliminating the need for an examiner as a necessary recipient of the visual task eliminates a potential source of error in visual acuity assessment: the human examiner. Furthermore, eliminating the need for a human examiner can save costs and / or time.

[0108] According to one embodiment, a preliminary preferred direction is selected in a numerical iterative method, initially taking into account only the ocular aberration data of at least one eye of the subject, and in at least one iteration step until a termination criterion is reached, the device aberration data of the optical device along the beam path of the device are additionally taken into account. Within the framework of the numerical iterative method, the target proximity can initially be determined without taking into account any cylindrical error of the target optics, e.g., solely based on the ocular aberration data and, if applicable, device aberration data without astigmatism, i.e., solely based on the refraction and any refractive error to be adjusted. Thus, in a first step, for example, only the astigmatism of the device can be omitted.The astigmatism of the ocular aberration data can be correctly taken into account from the beginning.

[0109] In an iteration step, which is carried out at least once or several times until the termination criterion is reached, a new preferred direction can first be determined by combining the astigmatism present at the current target proximity with the astigmatism of the subject's eye. Along the preliminary preferred direction determined by the axis of the combined, i.e. effective, astigmatism, the current curvature of the target wavefront is determined, as well as its deviation from the refraction, in other words the current refractive error in the preliminary preferred direction. The deviation of this current refractive error from the possible refractive error to be adjusted (or from 0, if no refractive error is to be adjusted) can be used to adjust the target proximity in the next iteration step by adjusting the target proximity by a predetermined fraction, e.g.a positive number up to and including 1, the deviation is changed in the direction that reduces the deviation of the refractive error. The termination criterion can then be checked at this new target proximity. If it has not yet been reached, the determination of the current provisional preferred direction of the current refractive error and the adjustment of the target proximity can be repeated until the termination criterion is met and / or a specified maximum number of repetitions is reached.

[0110] If the target optics of the optical device exhibit an astigmatic aberration, the uncorrected astigmatism of the eye and the astigmatism of the wavefront propagated through the beam path up to the entrance pupil of the eye can be calculated by combining them, the preliminary preferred direction can be determined accordingly, and the adjusted optotypes can be displayed aligned with the thus determined preliminary preferred direction. The combination can be achieved by adding and / or subtracting curvature matrices or power vectors, depending on the sign convention of the aberrations.

[0111] Within the scope of the invention, the preferred direction can be determined from the aberrations actually present when viewing the target and / or the optotypes displayed by the optical device, not just from the subject's ocular aberrations alone. The aberrations actually present when viewing the optotypes and / or the target can—but do not have to—be a function of the subject's target proximity and / or pupil size.

[0112] According to one embodiment, a refractive error in the principal section of an effective wavefront of the effective aberration data belonging to a preferred direction is generated when selecting the first and / or second preferred direction, in particular by means of the matrix equation: det(Weff(AT)−WΔS)=det(WF−WT(AT)−ΔS)=0

[0113] Where W ΔS a spherical wavefront with curvature ΔS of the refractive error, W eff (A T) the effective wavefront of the effective aberration data, W F the wavefront of the refractive error of at least one eye of the subject, and W T (A T ) which is determined by a target proximity A T dependent wavefront of a device aberration of the optical device along the optical path of the device.

[0114] In this way, a given refractive error and / or curvature ΔS, such as a fog, can be generated in the principal section belonging to the preferred direction. This allows a visual acuity to be measured at this refractive error ΔS. Analogous to the method described above, the more general matrix equation (3) is solved instead of the matrix equation (2). In this case, the one of the two solutions A (T,1) and A (T,2)The preferred direction should be selected to correspond to an effective wavefront that exhibits a greater magnitude of aberration in the principal section perpendicular to the preferred direction, i.e., a more disturbing aberration in the principal section along the preferred direction. In this preferred direction, astigmatism can generally be better reduced and / or compensated by the adjusted optotype than in the other direction.

[0115] In general, the astigmatic error of the optical path of the optical device can be counteracted not only by adjusting the axial position of the adjusted optotype to the preferred direction, but also or instead by adjusting the defocus to be adjusted, i.e., the refractive error ΔS. This can be done, for example, if the power is specified for the selected principal section. Alternatively or additionally, the specified power can be adjusted, especially if the power for the selected principal section is to be determined when a specific condition occurs, such as the recognizability of the optotype.

[0116] According to one embodiment, the method is carried out continuously with repeated adjustment of the preferred direction and / or a target proximity depending on a refractive error to be adjusted that varies in the preferred direction. The method can run continuously, wherein the adjustment of the preferred direction and the target proximity can take place in rapid succession depending on the refractive error to be adjusted in the preferred direction. In this way, it is possible to carry out visual acuity measurements with a changing refractive error in addition to visual acuity measurements with a static refractive error. For example, the refractive error can be used to correctly determine the level of refractive error up to which an optotype is displayed sharply, e.g. with increasing refractive error, and / or from which an out-of-focus optotype is displayed sharply, e.g. with decreasing refractive error.

[0117] According to one embodiment, the subject's visual acuity in the selected preferred direction is determined with two different optical powers applied, and from this, the subject's sensitivity is determined. For example, the visual acuity in the selected preferred direction can be determined once with the optimal and / or best optical power for this selected preferred direction, and again with a different optical power applied. This additional optical power can, for example, be shifted by ±0.5 dpt compared to the best power. The subject's sensitivity can be determined from the two visual acuity values ​​resulting for the subject with the two different optical powers (i.e., corrections).

[0118] In principle, sensitivity can also be determined based on two visual acuity values, neither of which is determined at the optimal correction. Using a mathematical model, the sensitivity of the eye and / or the subject can be calculated from the two determined visual acuity values. Thus, it is not necessary for the optimal correction to be known at the time of visual acuity determination.

[0119] Not all correction values ​​and / or visual acuity values ​​used for sensitivity measurement need to be recorded using the method according to the invention. For example, within the scope of an autorefractometric and / or aberrometric measurement, a first visual acuity can be determined, e.g., at a given distance from the objectively determined refraction, and a second visual acuity can be determined, e.g., within the scope of a subsequent subjective refraction, at the best optical correction resulting from the subjective refraction.

[0120] However, two or more visual acuity values ​​can also be recorded using the method according to the invention. For example, in the context of an autorefractometric and / or aberrometric measurement, a first visual acuity value can be determined at the objectively determined best correction, and a second visual acuity value at a given distance from it. The objective refraction determined in this way can be used as the best optical correction to calculate the subject's actual visual acuity.

[0121] According to one embodiment, a subjective and / or objective refraction is performed, and the subject's refractive error data is derived from the subject's refractive error determined thereby. For example, the ocular aberration data and / or the effective aberration data can be determined from an objective refraction, with the determined optimal optical corrections and the determined optimal axial position being used as ocular aberration data and / or effective aberration data. Alternatively or additionally, a subjective refraction can be performed. In this case, the ocular aberration data and / or the effective aberration data can be based on the result of the subjective refraction. Finally, the two results can also be combined, and an average of the objectively determined best correction and the subjectively determined best correction can be used as ocular aberration data and / or as the effective aberration data.Particularly in the context of a sensitivity determination, optical corrections that deviate from the determined best correction can also be used as eye aberration data and / or as the effective aberration data.

[0122] In one embodiment, for example, an objective refraction measurement is first performed on the test subject, and the best optical correction determined thereby is used as ocular aberration data. A subjective refraction is then performed, wherein two visual acuity values ​​are determined using the method according to the invention while the subjective refraction is being performed. The sensitivity is determined from these two visual acuity values. In particular, a visual acuity value is determined after completion of the subjective refraction on the basis of ocular aberration data and / or the effective aberration data resulting from the subjectively determined, best optical correction. In this embodiment, both an objective refraction and a subjective refraction are performed, the test subject's visual acuity is determined, and their sensitivity is determined. To determine the visual acuity, only a spherical optical correction is applied.Optical cylinder correction is not required.

[0123] According to one embodiment, the subject's visual acuity is determined using the method as a visual acuity characteristic and converted into a different visual acuity type. This conversion can be performed retrospectively. Thus, visual acuity usually depends on the optotype used. Since there are different methods for determining visual acuity, e.g., based on numbers or using a grating, e.g., FrACT, the visual acuity values ​​can depend on the determination method used. The measurement-method-dependent visual acuity values ​​can be converted into one another. The conversion can be performed using a calibration function that performs the desired conversion.

[0124] The calibration function can be determined using regression from a data set containing a variety of visual acuity values ​​and thus visual acuity types for the same person, determined using different measurement methods (e.g., based on numbers and FrACT). This allows the data set to be used to establish a correlation between the two different visual acuity types and / or visual acuity values. In the simplest case, the calibration function can be a function of the visual acuity determined using the method, and calculates the visual acuity value that would have resulted based on the other desired determination method as the function value.

[0125] To improve conversion accuracy, the calibration function can depend on additional parameters, e.g. the person's pupil diameter prior to visual acuity measurement, an orientation of the selected preferred direction, the adjusted optotypes used, the uncorrected optical power in one or both principal sections (e.g. in the best corrected or the most uncorrected principal section), additional parameters of the adjusted optotypes used (e.g. their contrast), or a combination of some or all of these parameters. Using the calibration function makes it possible to convert the visual acuity value determined using the method into a visual acuity value calculated using other methods, e.g. methods not provided with a directional feature.

[0126] According to one embodiment, the at least one adapted optotype is displayed without correction and / or without complete correction of a required optical cylindrical correction resulting from the effective aberration data, but nevertheless sharply represented for the test subject. In this case, image elements that appear sharp can be displayed to the test subject despite missing or incomplete correction of the effective astigmatic refractive error. For this purpose, the at least one image element is displayed as an adapted optotype, which is aligned with the preferred direction such that it is perceived as sharp by the test subject. This takes place without and / or without complete correction of the effectively required optical cylindrical correction. Because the at least one directional feature of the adapted optotype is displayed aligned parallel to the preferred direction, the test subject can perceive it sharply.This allows the adjusted optotype to be perceived sharply despite the lack of (complete) cylindrical correction, and can be focused on better and / or more easily by the subject than a blurred optotype. This can be advantageous, for example, when measuring accommodative ability, since subjects with uncorrected astigmatism are more likely to perceive an object becoming blurred.

[0127] For example, if an image of a hot air balloon is used as the target of a visual task, the direction in which the stripes on the hot air balloon run can be displayed parallel or perpendicular to the selected preferred direction. The subject can perceive the image of the hot air balloon with the stripes aligned in this way as a directional feature sharply, even without cylinder correction, and thus perceive it more quickly. The hot air balloon's stripe pattern can be displayed like a hatch, adjusted to the selected preferred direction.

[0128] This makes it possible to set a visual task with sufficient accuracy, e.g. when determining a refraction value and / or a visual acuity value without correcting the astigmatism of the subject and / or the optical device (or under incompletely corrected astigmatism).

[0129] One aspect relates to using adjusted optotypes each having a directional feature arranged parallel to a preferred direction determined from effective wavefront data to determine visual acuity characteristics and / or refractive characteristics of the subject for the selected preferred direction taking into account at least one dimension of the directional feature of the adjusted optotype.

[0130] The adapted optotype can be used, in particular, within the framework of the procedure described above. Therefore, all statements regarding the procedure can also apply to its use, and vice versa.

[0131] One aspect relates to an optical device for determining visual acuity characteristics and / or refraction characteristics of a subject who has a visual impairment. The device has a beam path through which optotypes can be displayed to the subject. For this purpose, the beam path can have a target optic for imaging the optotypes onto the subject's eye. The device has a selection module that selects a preferred direction depending on effective aberration data of the imaging of an optotype through the beam path of the optical device and through at least one ametropia eye onto the associated retina of the subject. The effective aberration data includes a combination of eye aberration data of the at least one ametropia eye of the subject with device aberration data of the optical device along the beam path of the device.A refraction unit is configured to apply an optical power to the subject at least in the selected preferred direction. The refraction unit can be designed, for example, as an aberometer and / or as a refractometer and / or apply a rotationally symmetric lens as sphere correction as the optical power. A display module has 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 characteristic determination module determines the visual acuity characteristics and / or refraction characteristics of the subject for the selected preferred direction, taking into account at least one dimension of the directional feature of the adapted optotype and the applied optical power.

[0132] The optical device can, for example, be used to perform the method described above and / or to use the adjusted optotypes described above. Therefore, all statements regarding the device also apply to the method and use, and vice versa.

[0133] For example, the dimension of the directed feature can be a distance between hatch lines, a contrast level, a thickness of lines and / or a width of gaps.

[0134] According to one embodiment, the device comprises an eye-tracking unit that tracks at least one eye of the subject while displaying the at least one adjusted optotype. Using the eye-tracking unit, the subject's gaze direction can be determined, and active and / or passive feedback from the subject can be registered as a response to a visual task.

[0135] In the context of this invention, the terms "substantially" and / or "about" 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.

[0136] Terms such as top, bottom, above, below, lateral, etc. refer - unless otherwise specified - to the Earth's reference system in an operating position of the subject matter of the invention.

[0137] The invention is described in more detail below with reference to exemplary embodiments shown in the figures. The same or similar reference numerals may denote the same or similar features of the embodiments. Individual features shown in the figures may be implemented in other exemplary embodiments. They show: Fig. 1 shows a schematic representation of an imaging optical system composed of a beam path and an eye according to an embodiment; Fig. 2A Examples of displayed optotypes for determining visual acuity; Fig. 2B which is suitable for the Fig. 2A shows the visual impression of a subject corrected for the second principal section of an effective aberration with cylindrical refractive error with an optical sphere correction; Fig. 2C which is suitable for the Fig. 2A shows the visual impression of a subject corrected for the first principal section of an effective aberration with cylindrical refractive error with an optical sphere correction; Fig. 3A shows embodiments of adapted optotypes for a visual task for a subject who is corrected for the second principal section of an effective aberration with cylindrical refractive error with an optical sphere correction; and Fig. 3B which is suitable for the Fig. 3A shows the visual impression of a subject corrected for the second principal section of an effective aberration with cylindrical refractive error using an optical sphere correction.

[0138] Fig. 1 shows a schematic representation of an imaging optical system 1 composed of a beam path of an optical device 10 and an eye 20 of a subject, according to one embodiment. The optical device 10 can have a display for displaying a target, in particular an optotype. The target is imaged onto the entrance pupil of the subject's eye 20 by a target optics along the beam path. The optical device 10 can have a light field display and / or a refraction unit and / or a display.

[0139] The optical device 10 can be arranged directly in front of the eye 20. The eye 10 can have a cylindrical refractive error, e.g., as a component of an ocular aberration of the subject. The optical device 20 can also have a further and / or different cylindrical imaging error, e.g., as a component of a device aberration.

[0140] When displaying an optotype using the optical device 10, the required light is projected both through the beam path of the optical device and through the subject's eye 20. The propagation direction of the wavefront required to display the optotype is Fig. 1 indicated as a dashed line.

[0141] This results in an effective wavefront W eff , which, as explained above, results from: Weff=WF−WT(AT).

[0142] Here W F the wavefront of the refractive error of at least one eye 20 of the subject and W T (A T ) which is determined by a target proximity A T dependent wavefront of a device aberration of the optical device 10 along the beam path of the optical device 10.

[0143] When displaying the adjusted optotype according to the invention, the effective aberration data are taken into account, which result, for example, from the effective wavefront W eff using equation (1) as a combination of the aberrations of the subject and the optical device 10.

[0144] In the Fig. 2 and Fig. Figure 3 shows embodiments of optotypes and the resulting visual impression for a subject and an optical device with an effective astigmatic refractive error. This assumes an effective refractive error in the sphere of +2.75 dpt and an effective astigmatism of -3.0 dpt at an axial position of 12°. These effective aberration data are to be understood as examples, and the following exemplary embodiments are generally applicable to subjects and optical devices that have an effective aberration in the sphere of s and an astigmatism of z at an axial position of α.

[0145] The subject's ocular aberration can be recorded as part of a subjective and / or objective refraction. The device aberration can be measured using a wavefront sensor. This results in effective aberration data, which includes the effective spherical and astigmatic aberration, including the axial position, for example, at least the value set {s; z; α}, in this example, the value set {+2.75 dpt; -3.0 dpt; 12°}.

[0146] Fig. Figure 2A shows examples of optotypes that can be displayed to the test subject to determine their visual acuity. Landolt rings are used as optotypes, with their gaps displayed from left to right at angles of 180°, 135°, 90°, 45°, and 0°. These five left Landolt rings are standard optotypes that can also be used in a conventional visual acuity test.

[0147] Right in Fig. Figure 2A shows two special and adapted optotypes in which the gap is displayed aligned to the angle 168° and 78°.

[0148] When determining visual acuity, an optical correction is applied and / or held in front of the subject, allowing the subject to view the optotypes and attempt to recognize them. This can be done using a refraction unit, which is positioned, for example, in front of the subject's eye or eyes.

[0149] For example, a refraction unit can be used that only allows the subject to perform optical spherical corrections, but not necessarily also optical cylindrical corrections. Thus, a refraction unit that only corrects spherical vision can be used, or a refraction unit that only allows for a limited range of axial positions and / or optical cylindrical corrections.

[0150] To determine the subject's visual acuity characteristics, a preferred direction is first selected from the effective aberration data. The preferred direction is a direction in a plane that can be approximately perpendicular to the subject's line of sight. The preferred direction can be located in the same plane in which the axial position of the effective cylindrical aberration is defined.

[0151] For example, either the axis position α can be selected as the preferred direction, thus representing the first principal section of the effective cylindrical aberration, or a direction perpendicular to it in the same plane, α +90°, thus representing the second principal section of the effective cylindrical aberration. In the example, the first preferred direction for the first principal section would be a direction of 12° in a plane approximately perpendicular to the subject's line of sight, and the second preferred direction for the second principal section would be a direction of 102° in a plane approximately perpendicular to the subject's line of sight.

[0152] 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 D. This correctly corrects the effective aberration in the first preferred direction, but not in the other directions, especially not perpendicular to the first preferred direction.

[0153] If the second preferred direction is selected, the refraction unit can apply an optical sphere correction of s+z to the subject, in this example -0.25 dpt (calculated from: +2.75 dpt - 3.0 dps). This correctly corrects the effective aberration in the second preferred direction, but not in the other directions, especially not perpendicular to the second preferred direction.

[0154] If, for example, the subject is given an optical sphere correction of -0.25 dpt, the effective aberration under the second preferred direction V2 at 102° is corrected relatively accurately. This correction is in Fig. 2B is shown schematically on the far left. Since the axial length of the effective aberration is normally determined with the subject's eyes in view, and the optotypes are usually displayed from the subject's perspective, the measurement angle of the axial position is exactly mirrored to 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 on which the optotypes are displayed, which corresponds to an axial position at a measurement angle of 102° with the subject's eyes in view.

[0155] For example, a vertically upward display angle (corresponding to "12 o'clock") corresponds to a 90° position. Likewise, a vertically upward measuring angle (corresponding to "12 o'clock") on the display plane corresponds to 90°.

[0156] A right-facing display angle at "3 o'clock" corresponds to 0°. However, this right-facing display angle corresponds to a measurement angle rotated to the left (mirror-inverted) with respect to the display plane, i.e., a measurement angle of 180°.

[0157] Therefore, there are different angle values ​​between the display angles defined on the display plane of the display and the measurement angles measured with a view of the subject's eyes.

[0158] Fig. Figure 2B shows the visual impression of the subject when looking at the Fig. 2A. The optotypes appear blurred, particularly in the direction perpendicular to the second preferred direction V2. Fig. The visual impression shown in Figure 2B is calculated for the subject from the example with the refractive error data {s=+2.75 dpt; z=-3.0 dpt; α=12°}.

[0159] As in Fig. As shown in Figure 2B, the optotypes in which the gap is displayed at the display angles of 90° and 45° appear particularly blurred to the subject.

[0160] 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 the display angles 168° and 348°. The adapted Landolt ring at the display angle 168° is also Fig. 2A shows 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 edge to the white gap and back to the black circle 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 subject, cf. the two right-hand visual impressions in Fig. 2B. This is because the effective aberration in the second principal section, i.e. along the second preferred direction V2, is fairly well and / or optimally corrected by the provision of the optical sphere correction of -0.25 dpt.

[0161] The directional feature of the Landolt rings, whose gap is displayed at angles of 90° and 45°, is relatively steep (i.e., almost perpendicular) to the corrected second preferred direction V2, resulting in a severely blurred visual impression, particularly for these two optotypes. However, blurred visual impressions also occur for the other standard optotypes, making an accurate visual acuity determination impossible.

[0162] If the subject is given an optical sphere correction of +2.75 dpt, the effective aberration under the first preferred direction V1 at a measurement angle of 12° is relatively accurately or optimally corrected. This correction is Fig. 2C is indicated on the far left. This axis length at the measurement angle of 12° appears on the display in the display plane at a display angle of 168°. Thus, the first preferred direction V1 is aligned at a display angle of 168° on the display.

[0163] Fig. 2C shows the visual impression of the subject when looking at the Fig. 2A. The optotypes appear blurred, particularly in the direction perpendicular to the first preferred direction V1. Fig. The visual impression shown in Figure 2C is again calculated for the subject from the example with the effective aberration data {s=+2.75 dpt; z=-3.0 dpt; α=12°}.

[0164] As in Fig. As shown in Figure 2C, the standard optotypes, in which the gap is displayed at the display angles 180°, 135°, and 0°, appear particularly blurred to the subject.

[0165] 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 the display angles of 258° and 78°. The adapted Landolt ring at the display angle of 78° is also Fig. 2A shows 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 edge to the white gap and back to the black circle 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 subject, cf. the two right-hand visual impressions in Fig. 2C. This is again due to the fact that the effective aberration in its first principal section, i.e. along the first preferred direction V1, is fairly well and / or optimally corrected by the provision of the optical sphere correction of +2.75 dpt.

[0166] The directional feature of the Landolt rings, whose gap is displayed at the display angles 180°, 135°, and 0°, is relatively steep (i.e. almost perpendicular) to the corrected first preferred direction V1, which is why a very blurred visual impression results, especially for these three optotypes.

[0167] As part of a visual task to determine visual acuity, the test subject, corrected in his second preferred direction V2 with his optical sphere correction of -0.25 dpt, can now be asked where the gaps of the two optotypes displayed at the display angles 168° and 348° point, e.g. whether they point more to the left or to the right.

[0168] Alternatively or additionally, the subject, corrected in his first preferred direction V1 with his optical sphere correction of +2.75 dpt, can be asked, in the context of another visual task to determine visual acuity, where the gaps of the two optotypes displayed at the display angles 258° and 78° point, e.g. whether they point more upwards or downwards.

[0169] This allows us to determine whether the subject can still recognize the directed feature as a detail of the adjusted optotype. Depending on the size of the detail the subject can still recognize, the visual acuity for the selected preferred direction V1 and / or V2 can be determined.

[0170] For the calculation of the resulting visual impression, which is Fig. 2B and Fig. 2C and the subsequent 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, with the image having a side length of 204.8 mm and the side length of a pixel corresponding to 40 µrad = 0.1375 arc minutes.

[0171] The Snellen E test belongs to the same category of adjusted optotypes as the Landolt rings. The relevant feature, i.e., the directional feature of the Snellen E test, 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 bar.

[0172] If necessary, the bright background above and / or below may also form part of the sequence. Thus, when using Snellen E-lines, the longitudinal line connecting the transverse lines must be oriented parallel to the selected and corrected preferred direction V1 or V2, which, like the Landolt ring, only allows two different orientations.

[0173] Fig. Figure 3A shows additional adjusted optotypes for the subject with the effective aberration used as an example. The adjusted optotypes used are borderless, hatched 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°.

[0174] The hatching lines of each optotype all have the same thickness and the same orientation. Any two adjacent hatching lines are always at the same, constant distance from each other.

[0175] The hatch lines provide a directional feature of the adjusted optotypes. The direction of the directional feature is the direction of the alternation of the light and dark areas, i.e., the direction perpendicular to the hatch lines.

[0176] If the subject is corrected by applying a purely spherical optical correction of -0.25 dpt for his second preferred direction V2, the subject will have the Fig. The visual impression is shown in Figure 3B. The first, third, and fourth optotypes from the left appear as gray spots, while the hatching of the second optotype can be recognized by the subject.

[0177] The test subject can thus identify the adjusted optotype that differs from the others in a visual task for determining visual acuity. 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° corresponding to the measurement angle of 102°, i.e., the second principal section of the effective cylindrical aberration.

[0178] The distance between two adjacent hatching lines and / or the thickness of the black hatching lines can be used as the size of the detected detail to determine the visual acuity. Visual tasks

[0179] To determine visual acuity, the test subject can be given visual tasks in which adapted optotypes are displayed. When it comes to visual tasks, a distinction can be made between visual tasks with active and passive feedback from the test subject. Active feedback can be understood as a statement from the test subject, which can be given either verbally or by consciously looking at an optotype and recording the direction of gaze using eye tracking. Passive feedback can be understood as following a presented optotype that is moving. Based on eye movement recorded by an eye tracking unit, it can be determined whether the optotype is still reliably recognized.

[0180] The optotypes are displayed using a defined presentation style and thus presented to the test subject. A presentation style refers to properties such as contrast, size, or frequency of the hatching. Size is a particularly important property for optotypes of the type that can be displayed in two mirror-inverted ways with respect to the selected preferred direction, such as Landolt rings and Snellen E's. Hatching frequency is a particularly important property for optotypes of the type that have hatched areas and / or consist of hatched areas.

[0181] The presentation style may be impaired by changing the presentation style to make it less recognizable, e.g. by reducing the size (particularly in the case of adapted optotypes of the type that can be displayed in two mirror-inverted ways with respect to the selected preferred direction), reducing the contrast and / or increasing the frequency of hatching (particularly in the case of adapted optotypes of the type that have hatched areas and / or consist of hatched areas).

[0182] In one embodiment of a visual task with active feedback, one or more customized optotypes of the type shown are presented, which can be displayed in two mirror-inverted ways with respect to the selected preferred direction. The subject is expected to recognize the orientation of these displayed optotypes.

[0183] Displaying multiple optotypes of the same presentation allows for a more reliable assessment of the response. A deterioration in the presentation to the point where the optotypes can no longer be recognized allows for the determination of visual acuity.

[0184] In one embodiment of a visual task with active feedback, one or more customized optotypes of the type that have and / or consist of hatched areas are presented. The subject is asked to detect the presence of hatching in the optotype.

[0185] Displaying multiple optotypes of the same presentation allows for a more reliable assessment of the response. A deterioration in the presentation to the point where the optotypes or the presence of a hatching pattern can no longer be recognized allows for the determination of visual acuity.

[0186] Furthermore, one or more adapted optotypes with an adapted orientation can be presented, as well as one or more adapted optotypes with a different orientation, e.g., with an orthogonal orientation. For optotypes of the type 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 detect differences and / or which one or more optotypes differ from the others. This type of visual task is also referred to as a "forced choice."

[0187] In one embodiment of a visual task with passive feedback, one or more adapted optotypes of one of the aforementioned types are presented in a moving state. The presentation type can be continuously and / or gradually degraded. Based on the eye movement recorded by an eye-tracking unit, it is then possible to determine the presentation conditions under which the optotype and / or visual object can still be reliably recognized. From this, the subject's visual acuity can be derived and / or determined.

[0188] The optotypes can be displayed using a light-field display. The applied optical sphere corrections do not need to be physically applied, but can be simulated as wavefronts. Characterization of the target optics and / or device aberration

[0189] According to the invention, the effective aberration, which is composed of the ocular aberration and the device aberration, is taken into account when selecting the preferred direction. At least one of the detection methods described below can be used to detect the device aberration, in particular the information about the target optics to be taken into account, in particular the astigmatic error generated by the target optics. Measuring the target optics of the optical device

[0190] The imaging properties, in particular the astigmatism, of the target optics in the beam path of the optical device can be measured, e.g. if no assumptions are used.

[0191] For this purpose, a point light source can be arranged at the location of a display on the optical device, which can be designed as a display, for example. This can be achieved, for example, by temporarily introducing a point light source at the position of the display and / or by switching on one or a few pixels of the display. The emerging light field can be measured using one of the known methods, e.g., using (Shack)-Hartman sensors, using interferometric methods, and / or by evaluating an intensity distribution of the emerging wavefront by fitting an ellipse and determining the semi-axis(es) of this ellipse.

[0192] Alternatively, a point light source can be inserted in place of the emerging wavefront, and a sensor can be inserted in place of the display. In this case, the measurement is performed backward, so to speak, through the beam path of the optical device.

[0193] Furthermore, you can work with the display of patterns instead of a single light point.

[0194] Details of the implementation of some of the above-mentioned and other possible measurement methods are disclosed, for example, in D. Malacara: “Optical Shop Testing”, 2nd edition, J. Wiley & Sons (1992). Characterization of components or modules of the optical device

[0195] As an alternative to measuring a light field, components and / or pre-assembled modules made up of multiple components of the optical device can also be measured to determine the light field. All or just one and / or several components and / or modules can be measured, in particular those with the highest (manufacturing) tolerance and / or whose tolerance has the greatest impact on the light field. The calculation can be simplified by considering the component(s) and / or module(s) with the highest (manufacturing) tolerance while neglecting the other components and / or module(s) with lower (manufacturing) tolerance.

[0196] Furthermore, individual properties (e.g. at least one position or tilt of a lens and / or a beam splitter) of components or modules can be measured and others (e.g. curvatures of the surfaces of the lens and thickness of the beam splitter) can be assumed and parameters for describing the astigmatic error of the device can be derived therefrom.

[0197] The measurements can be carried out either individually on the individual component and / or module or on one or more components representative of a batch (e.g. using the mean or median). Consideration of known properties of components of the optical device

[0198] In another case, it is possible to work only with known values ​​without measurements.

[0199] This is the case, for example, when individual components and / or the design of the associated imaging optics introduce known imaging errors into the system, e.g. an astigmatism of oblique beams due to inclined beam splitters. Dependence on the set effect

[0200] When measuring the target optics or individual components and / or modules according to the previous sections, measurements can be taken for several different optical effects and / or the behavior for other effects can be derived from one or more measurements based on model assumptions.

[0201] When characterizing with measured or assumed properties of individual components or modules according to the previous sections, the astigmatic error of the target optics can be calculated as a function of the assumed optical effect, for example, by reading the corresponding positions of the components and / or modules to each other and / or their properties as a function of the configuration necessary for the assumed optical effect, such as distances between individual optical components, into the calculation.

[0202] In the following, additional aspects within the scope of the invention which can be carried out independently of the method presented so far are disclosed. Display of sharply appearing image elements despite incomplete correction of the visual impairment

[0203] By combining any device aberrations along the beam path of the optical device with the eye aberration of the eye, or alternatively without taking the device aberrations into account, elements of an image displayed by the optical device through the beam path can be aligned on the basis of the preferred direction determined according to the invention in such a way that they are perceived as sharp by the subject.

[0204] This can be carried out independently of a visual acuity determination or as part of other measurements. For example, the method can also be used to determine the accommodative capacity of the test subject's eye. When measuring the accommodative capacity of the eye, a target can be displayed as an object gets closer and closer, regardless of uncorrected astigmatic refractive error. If the displayed object is sharply displayed, it can be fixated on more easily, which can be particularly advantageous when measuring accommodative capacity, since subjects with uncorrected astigmatism perceive blurring of the viewed object more quickly. If, for example, the image of a hot air balloon with a striped pattern is used as the target, the direction in which the stripes run can be selected and displayed perpendicular to the preferred direction determined using the method according to the invention.

[0205] This embodiment thus relates to a method in which the effective aberration data is provided as described above and the preferred direction is selected therefrom. In the same way, the optical power can be applied at least in the selected preferred direction. In contrast to the method for determining visual acuity characteristics and / or refractive characteristics of a subject, however, in the method for determining the accommodative ability, an adapted optotype is not necessarily displayed and the visual acuity characteristics and / or refractive characteristics are not determined depending on the directional feature of the adapted optotype, but rather a target with at least one directional feature is displayed. The directional feature can, for example, be designed as a striped pattern and the target as an image with this same striped pattern.

[0206] The optical device displays the target in such a way that its directional feature is parallel to the preferred direction. The subject's accommodation ability can then be determined based on the displayed target. Compensation of non-central aberrations

[0207] In addition to directional central aberrations such as astigmatism and / or coma, non-central aberrations such as distortions and chromatic aberration, i.e. wavelength-dependent distortion, can also be compensated within a limited scope. For this purpose, the adjusted optotypes can be designed in such a way that their image compensates for the aberrations caused by the beam path and / or the target optics. For this purpose, a transformation is applied to the, for example, undistorted adjusted optotypes, which compensates for any non-central aberration caused by the target optics. The non-central aberrations can be characterized using models in a similar way to the method described above. For example,Target wavefronts generated by point light sources at different positions on the target display are characterized using models that depend on the position of the point light source. To characterize chromatic aberration, the point light sources can be examined at different wavelengths corresponding to the wavelengths emitted by the screen. List of reference symbols 1 optical system 10 optical device 20 eyes V1 first preferred direction V2 second preferred direction QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2022 209 490

[0007] Cited non-patent literature

[0000] D. Malacara: “Optical Shop Testing”, 2nd edition, J. Wiley & Sons (1992

[0194]

Claims

[1] Method for determining visual acuity characteristics and / or refraction characteristics of a subject who has a visual impairment, by means of an optical device (10) for displaying optotypes, which has a beam path through which the optotypes are displayed to the subject, comprising the steps: - Providing effective aberration data of the image of an optotype through the beam path of the optical device (10) and through at least one ametropia-related eye (20) onto the associated retina of the subject, wherein the effective aberration data include a combination of eye aberration data of the at least one ametropia-related eye of the subject with device aberration data of the optical device along the beam path of the device; - selecting a preferred direction (V1; V2) depending on the effective aberration data, in particular on the basis of effective wavefront data belonging to the effective aberration data; - Creating an optical effect at least in the selected preferred direction; - displaying at least one adapted optotype having a directional feature, wherein the adapted optotype is displayed in such a way that its directional feature is arranged parallel to the preferred direction (V1; V2); and - Determining the visual acuity characteristics and / or refraction characteristics of the subject for the selected preferred direction (V1; V2) taking into account at least one dimension of the directional feature of the adjusted optotype and the applied optical power. [2] The method of claim 1, wherein the effective aberration data includes an astigmatism of the at least one ametropia-impaired eye and / or the optical device. [3] Method according to claim 1 or 2, wherein the device aberration data of the optical device (10) depend on and / or comprise a function of a target proximity, wherein the target proximity corresponds to a mean curvature of a wavefront propagating along the beam path of the optical device (10), in particular in a pupil plane of the at least one ametropia-impaired eye (20). [4] Method according to one of the preceding claims, wherein the device aberration data of the optical device depend on and / or comprise a pupil size of the at least one ametropia-impaired eye. [5] Method according to one of the preceding claims, wherein the device aberration data of the optical device (10) are acquired as fixed device parameters of the optical device and / or as a function of adjustable device parameters of the optical device (10). [6] Method according to one of the preceding claims, wherein the device aberration data of the optical device (10) are measured by means of a wavefront sensor. [7] Method according to one of the preceding claims, wherein when selecting the preferred direction, the effective aberration data is used as the effective wavefront W eff = W F - W T (A T ) are taken into account, where W F the wavefront of the visual impairment of at least one eye of the subject and W T (A T ) which is determined by a target proximity A Tdependent wavefront of a device aberration of the optical device along the beam path of the optical device. [8] Method according to one of the preceding claims, wherein at least a first and / or second principal section of an effective wavefront of the effective aberration data is selected as the first and / or second preferred direction and / or a direction in which a curvature matrix of the effective wavefront of the effective aberration data has an eigenvalue of 0, in particular by means of the matrix equation: det(Weff(AT))=det(WF−WT(AT))=0; where W eff (A T ) denotes the effective wavefront of the effective aberration data, W F the wavefront of the visual impairment of at least one eye of the subject and W T (A T ) which is determined by a target proximity A Tdependent wavefront of a device aberration of the optical device along the optical path of the optical device. [9] The method of claim 8, wherein: - an axial position is selected as a first preferred direction (V1), which is arranged in the first principal section of the effective wavefront of the effective aberration data, and an optical sphere correction is applied as the optical effect, which corrects the ametropia of the subject and / or the optical device in the first principal section of the effective wavefront of the effective aberration data according to the effective aberration data, and wherein the visual acuity of the subject for this first principal section is determined as the visual acuity characteristics; and / or - an axial position is selected as a second preferred direction (V2), which is arranged in the second principal section of the effective wavefront of the effective aberration data, and an optical sphere correction is applied as the optical effect, which corrects the ametropia of the subject and / or the optical device in the second principal section of the effective wavefront of the effective aberration data according to the effective aberration data, and wherein the visual acuity of the subject for this second principal section is determined as the visual acuity characteristics. [10] Method according to one of the preceding claims, wherein the directional feature of the adjusted optotype comprises a sequence of light and dark areas which follow one another along the preferred direction (V1; V2). [11] Method according to one of the preceding claims, wherein the adjusted optotype used is: - a Landolt ring whose gap is displayed rotated by 90° to the selected preferred direction (V1; V2); and / or - a Snellen E, in which the connecting line connecting the three parallel E lines is arranged parallel to the selected preferred direction (V1; V2); and / or - a hatched area in which the hatching lines are arranged perpendicular to the selected preferred direction (V1; V2). [12] 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 tuple pair and / or at least one refraction value is determined as visual acuity characteristics and / or refraction characteristics. [13] Method according to one of the preceding claims, wherein the subject is presented with at least one visual task dependent on the displayed adjusted optotype, which the subject answers by providing active and / or passive feedback. [14] Method according to one of the preceding claims, wherein in a numerical iterative method a preliminary preferred direction is selected taking into account initially only the eye aberration data of at least one eye of the subject, and in at least one iteration step until a termination criterion is reached, the device aberration data of the optical device along the beam path of the device are additionally taken into account. [15] Method according to one of the preceding claims, wherein a refractive error in the principal section of an effective wavefront of the effective aberration data belonging to a preferred direction is generated when selecting the first and / or second preferred direction, in particular by means of the matrix equation: det(Weff(AT)−WΔS)=det(WF−WT(AT)−ΔS)=0; where W ΔS a spherical wavefront with curvature ΔS of the refractive error, W eff (A T ) the effective wavefront of the effective aberration data, W F the wavefront of the refractive error of at least one eye of the subject, and W T (A T ) which is determined by a target proximity A T dependent wavefront of a device aberration of the optical device along the optical path of the device. [16] Method according to one of the preceding claims, wherein the method is carried out continuously with repeated adjustment of the preferred direction and / or a target proximity as a function of a refractive error to be adjusted which is variable in the preferred direction. [17] Method according to one of the preceding claims, wherein a subjective and / or objective refraction is carried out and the refractive error data of the subject are derived from the refractive error of the subject determined thereby. [18] Method according to one of the preceding claims, wherein the at least one adjusted optotype is displayed without correction and / or without complete correction of a required optical cylinder correction resulting from the effective aberration data and is nevertheless displayed sharply for the subject. [19] Optical device for determining visual acuity characteristics and / or refractive characteristics of a subject who has a visual impairment, comprising: - a beam path through which optotypes can be displayed to the test subject; - a selection module which selects a preferred direction depending on effective aberration data of the image of an optotype through the beam path of the optical device and through at least one ametropia-impaired eye onto the associated retina of the subject, wherein the effective aberration data include a combination of eye aberration data of the at least one ametropia-impaired eye of the subject with device aberration data of the optical device along the beam path of the device; - a refraction unit configured to apply an optical effect to the subject in the selected preferred direction; - a display module with a display which displays 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 characteristic determination module which determines the visual acuity characteristics and / or refraction 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 and the applied optical power.

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