Device for the precision measurement of visual acuity and / or refraction and its use

Description

[0001] The invention relates to a device for the precision of visual acuity measurements and / or the determination of refraction and the associated use of such a device.

[0002] A visual acuity test measures visual acuity (visual acuity). This can be done using conventional optotypes placed at a certain distance from the patient, who is asked to assess the extent to which they can recognize elements of these optotypes. This can be used to determine a visual impairment. Alternatively, compact viewing devices can be used to create consistent lighting conditions in a small space.

[0003] Other procedures use devices that measure the eye and can thus determine refractive errors.

[0004] Refraction is the refractive power that an optical correction has to produce a sharp image in the eye at infinite distance.

[0005] During a refraction test, the patient looks at a chart through a measuring device, such as a phoropter or trial glasses. To determine the exact corrective lenses, lenses are gradually inserted or removed into or from the measuring device until the refractive error is corrected and the patient can see the smallest possible elements of the chart.

[0006] Here, the optotype display is located at a finite distance from the measuring device. According to DIN 58220, a minimum of four meters is generally required; in practice, this distance can be ten meters or more due to mirror deflection.

[0007] The problem here is that visual acuity is defined at an infinite distance. The typically used distance a of 4 to 10 m can only achieve partially satisfactory results, as the range from 4 to 10 m only partially approximates infinite distance. Since the optotype representation is not at infinity, the eye accommodates to the refractive distance, which can result in a refractive error.

[0008] According to the current state of the art, the refractive error is either ignored or a cursory re-determination is performed by the optician and / or ophthalmologist. The patient, while wearing the previously determined lenses, determines the extent to which their vision is corrected by looking into the distance. This can be done, for example, outside the optician's shop or doctor's office, or by otherwise observing the distance, such as through a window.

[0009] From US 2012 / 0154 742 A1 the use of an electro-optical phoropter for determining refraction is known.

[0010] US 2017 / 119247A1 and US 2015 / 0116666A1 disclose viewing devices in which the respective optotype display is positioned just a few centimeters from the eye. WO2018 / 078409A1 discloses glasses that have a display for each eye.

[0011] The object of the present invention is to provide a device with which the refractive error is minimized or even eliminated.

[0012] This object is achieved by a device having the features of claim 1.

[0013] The additional lens arrangement spherically compensates and parallelizes the beam path or rays in the beam path between the eye, or rather its pupil, and the measuring device, i.e. a phoropter or trial glasses, creating an effect that would occur if the distance a were to extend to infinity. Without the use of at least one additional lens arrangement, a refractive error equal to the inverse of the distance between the eye and the optotype display occurs. Consequently, at a distance a of 4 meters, a refractive error of up to 0.25 dpt can occur. By using at least one additional lens arrangement, the refractive error can be spherically compensated. This makes it possible to provide optical correction, for example through spectacle lenses or contact lenses, that optimally meets the patient's needs.Consequently, precise refraction determination, which at least largely eliminates the refractive error, makes it possible to see clearly even objects that are located far away from the patient, despite poor vision. The patient thus receives optical correction that meets their physiological needs. Visual acuity and / or refraction are measured individually for each eye or simultaneously for both eyes.

[0014] This additional lens arrangement, which can consist of one or more lenses, is designed to parallelize the rays within the beam path between the eye and the measuring device, thus at least largely or completely eliminating refractive errors. This can be achieved, in particular, by an additional lens arrangement comprising multiple lenses or by a single suitable lens.

[0015] Furthermore, it is conceivable to provide a certain number of lenses, each allowing a certain range of refractive errors, in order to use commercially available lenses.

[0016] The at least one additional lens arrangement and / or prism arrangement is arranged in particular in and / or on a phoropter or trial frame. It is conceivable to retrofit existing measuring devices or to install this at least one lens in and / or on new devices. Consequently, the user, for example, an optician or ophthalmologist, can obtain more precise results without any adjustments or major adjustments.

[0017] The optotype display is intended to be positioned at a distance a of at least 2 m, and preferably 4 m to 10 m, from the eyes. This allows for adaptation to the spatial conditions and an examination in accordance with DIN 58220.

[0018] The additional lens arrangement is arranged on the side of the measuring arrangement facing the optotype display.

[0019] According to the invention, at least one prism arrangement is provided which deflects the light from the optotype display falling into the observing eyes in such a way that the fixation line of the respective eye runs at least largely through the center of the measuring device and / or parallel to the fixation lines of the other eye. In other words: the fixation line of the respective eye then runs perpendicular to the lens plane of the measuring device or the additional lens arrangement. If both eyes view the optotype display simultaneously, the fixation lines of the two eyes run at least largely parallel to one another. The fixation line is understood to be the straight line connecting the exit point of the light from the prism arrangement and the center of the entrance pupil of the eye. The center of the measuring device is understood to be the exit point of the light from the measuring device at which the person must look in order for the measuring device to deliver correct measurement values.The prism arrangement thus provides a prismatic compensation that ensures at least a largely parallel position of the eyes. Without the prism arrangement, the fixation lines of the two eyes would noticeably converge toward the optotype display.

[0020] For example, with a pupillary distance PD of both eyes of PD = 66 mm, each eye has a pupillary distance to an imaginary midline of PD R / L = 33 mm. At a distance a = 4 m from the optotype display, this results in a prismatic error of F p R / L = 0.825 cm / m for each eye, where: F p R / L = PD R / L / a = 0.825 cm / m.

[0021] To compensate for the prismatic error F p , a prism arrangement is required that at least largely compensates for the prismatic error of F p R / L in each eye. Ideally, the prismatic correction p of each eye is exactly the value of the prismatic error F p R / L .

[0022] If the spherical error is corrected and the prismatic error is not corrected, this results in an unnatural decoupling of vergence and accommodation. Furthermore, the person then does not look vertically through all the lenses of the measuring device, which increases the aberrations of these lenses and indicates a refractive error that, although usually corrected during refraction, does not exactly correspond to the person's refractive error.

[0023] The spherical compensation of the additional lens arrangement and the prismatic compensation of the prism arrangement resolve these problems. Due to the spherical compensation, the optotype is projected at infinity, regardless of the actual distance a. This makes it possible to measure even short distances to the optotype without compromising refraction quality. Due to the prismatic compensation, a prismatic correction is measured for infinity, also regardless of the actual distance a. If the spherical and prismatic compensations are superimposed, this results in a synergistic effect that ultimately delivers optimal measurement values.

[0024] The prism arrangement is arranged on the side of the additional lens arrangement facing the optotype display. This allows the user, for example an optician or ophthalmologist, to adapt the additional lens arrangement and the prism arrangement to their individual needs and the conditions of the measuring or destination location. In particular, the arrangements can be adapted to the measuring device used. An exemplary arrangement according to the invention within the measuring device can be seen in Fig. 2 in a pair of measuring glasses, an exemplary arrangement according to the invention directly behind the measuring device, here a phoropter, shows Fig. 3 , as explained in more detail below.

[0025] According to the invention, the additional lens arrangement is provided on the side of the measuring arrangement facing the optotype display, and the prism arrangement is provided on the side of the additional lens arrangement facing the optotype display. From the patient's perspective, the measuring device is then located directly in front of their eyes, the additional lens arrangement is located behind the measuring device, and the prism arrangement is located behind the additional lens arrangement. Such an arrangement can, in particular, prevent harmful oblique vision.

[0026] Advantageously, it can further be provided that the additional lens arrangement and / or the prism arrangement are adjustable. The refractive power of the lens arrangement can be adjustable to adjust the lens arrangement. A prism compensator, for example, can be used to adjust the prism arrangement. This embodiment has the advantage that the additional lens arrangement and the prism arrangement can be delivered together with the measuring device, and that, depending on local conditions, the additional lens arrangement and the prism arrangement can then be adjusted depending on the distance of the optotype display from the measuring device and also depending on the interpupillary distance of the respective patient.

[0027] It has also proven advantageous if the additional lens arrangement and / or the prism arrangement are combined in an optical unit. Such an optical unit can then preferably be mounted directly on the measuring device and adapted to the local conditions.

[0028] It makes sense to use additional lens arrangements which have a refractive power b that depends on the distance a between the eye and the visual acuity, and for which the following applies: b = 1 / a or b = 1 / a + / - r, where r is any rounding tolerance. It is most advantageous if the refractive power is b = 1 / a, as this compensates for 100% of the refractive error.

[0029] To ensure practical application, it may be useful to allow rounding tolerances r so that one and the same lens can be used for different distances a.

[0030] It is particularly conceivable to allow a range of rounding tolerances from r = + / - 1 / 10 to + / - 1 / 30 diopter (D), especially from r = + / - 1 / 20 D. This results in a refractive error with a rounding tolerance of r = + / - 1 / 20 D being limited to a maximum of 0.049 D, thus minimizing the refractive error by 80%.

[0031] The rounding tolerance r can be selected such that for the range from 4 to 10 m only four different additional lens arrangements, i.e. additional lens arrangements with only four different refractive powers b, are required to adequately compensate for the refractive error FR: For a distance a of 4.00 m, a first additional lens arrangement is required with a refractive power of 0.25 dpt. For a distance of 4.10 m to 5.10 m, a second additional lens arrangement is required with a refractive power of 0.2 dpt. For a distance of 5.20 m to 6.90 m, a third additional lens arrangement is required with a refractive power of 0.15 dpt. For a distance of 7.00 m to 10.00 m, a fourth additional lens arrangement is required with a refractive power of 0.1 dpt.

[0032] It is sensible to use prism arrangements that have a prismatic compensation p that depends not only on the distance a, but also on the distance PD of the pupils, and for which the following applies: p = PD R / L / a or p = PD R / L / a + / - R, where PD R / L is half the pupil distance of the eyes; R is the rounding tolerance. It is most advantageous if the prismatic compensation is p = PD R / L / a, as this compensates for unwanted convergence 100%.

[0033] To ensure practical application, it may be useful to allow rounding tolerances R so that one and the same prism arrangement can be used for different distances a.

[0034] It is particularly conceivable to provide a first prism arrangement per eye for a distance a of 4.00 m, the prismatic compensation p = 0.65 cm / m. For a distance of 4.10 m to 5.10 m, a second prism arrangement is advantageous, the prismatic compensation p = 0.51 cm / m. For a distance of 5.20 m to 6.90 m, a third prism arrangement per eye results, the prismatic compensation p = 0.38 cm / m. For a distance of 7.00 m to 10.00 m, a fourth prism arrangement per eye results, the prismatic compensation p = 0.26 cm / m.

[0035] Furthermore, the auxiliary lens assembly and / or prism assembly can be permanently or detachably mounted on the measuring device. A permanent assembly has the advantage that a one-time installation of the auxiliary lens assembly and prism assembly always achieves the desired correction, without the risk of distorting the result, for example, due to slipping or displacement of the auxiliary lens assembly and / or prism assembly. This also eliminates the possibility of accidentally using the wrong lens or prism.

[0036] A detachable arrangement has the advantage that a measuring device can be used in different situations, for example different rooms or different distances from an optotype display, and by using different additional lens arrangements and / or prism arrangements, an optimal result can still be achieved.

[0037] Ideally, at least one additional lens arrangement and / or prism arrangement is located between the measuring device and the optotype display, or within the measuring device itself, or between the patient and the measuring device. A combination of these options is also conceivable. This has the advantage of allowing the individual needs of the user to be met.

[0038] The device described here can be used to measure a patient's visual acuity or determine their refraction. Its use has the advantage of compensating for the existing inaccuracy.

[0039] Further advantages and advantageous embodiments of the invention will become apparent from the following description, based on which the embodiments shown in the figures are described and explained in more detail.

[0040] They show: Figure 1a shows a device according to the known prior art, Figure 1b shows a device according to the invention, Figure 2 shows an arrangement of an additional lens arrangement on trial glasses, Figure 3 shows an arrangement of an additional lens arrangement on a phoropter, Figure 4 shows a schematic plan view of a device according to the prior art, Figure 5 shows a schematic plan view of a device according to the invention, and Figure 6 shows an assignment of the refractive error and the prismatic error as a function of the distance a and the use of a suitable additional lens arrangement and prism arrangement.

[0041] In the Figure 1aA device 10 for testing visual acuity and / or determining refraction according to the known prior art is shown. The device 10 comprises a measuring device 12 and an optotype display 14, wherein the optotype display 14 is arranged at a distance a from a human eye 16 or its pupil 18, and wherein the measuring device 12 is located between the eye 16 and the optotype display 14.

[0042] The measuring device 12 can, for example, be a pair of measuring glasses as shown in Figure 2 shown, or a phoropter as shown in Figure 3 shown, act.

[0043] Furthermore, the beam path 16 of the light between the measuring device 12 and the optotype display 14 is shown. The beam path between the pupil 18 and the measuring device 12 is shown in Figure 1amarked with the reference symbol 5'; the eye lens with 19. The beam path 5' is or the rays in the beam path 5' are not parallel, but slightly convert from the eye 16 to the measuring device 12. Since the optotype display 14 is not at infinity, the eye 16 accommodates to the refraction distance. The eye lens 19 is due to the slight near adaptation in Fig. 1a depicted somewhat thickened; the eye does not "relax" to infinity.

[0044] In the Figure 1b , which shows a device 20 according to the invention, an additional lens arrangement 22, for example in the form of a lens, is additionally provided on the measuring device 12. The additional lens arrangement 22 directs the rays in the beam path 5 into Figure 1b between the pupil 18 and the measuring device 12, thereby producing an effect that would exist if the distance a were to move to infinity.

[0045] The refractive power of the additional lens arrangement 22 to achieve this effect is calculated from the inverse of the distance a. Due to the refraction of the additional lens arrangement 22, the observing eye 1 perceives the light of the optotype display 14 in such a way that the distance a tends towards infinity. As a result, the refractive error FR = 1 / a approaches the value zero. The eye 16 thus accommodates towards infinity; the eye lens 19 is in Figure 1b correspondingly thin and relaxed. When measuring using the device 20 according to the invention, the refractive error FR or any associated undesirable inaccuracy can therefore be compensated.

[0046] Unlike in the Figure 1bAs shown, it is conceivable that the additional lens arrangement 22 is located between the measuring device 12 and the eye 16. It can also be a combination of different lenses that are located together in front of, together behind, or split in front of and behind the measuring device 12, with the sum of the refractive indices ideally being 1 / a or 1 / a + / - r. A further embodiment variant can provide for one or more lenses to be located within the measuring device 2.

[0047] In Figure 2a one can see the front view of a measuring frame 30 according to the invention, in Figure 2b the side view. Here you can see that the additional lens arrangement 22 is located inside the frame. It also shows Figure 2b, such as lenses 32, 34 located in front of and behind the trial frame 30, which can be used variably for the actual refraction determination. These are mounted on the trial frame 30 by holders 36. However, the additional lens arrangement 22 could also be mounted on the holders 36 to meet the respective model or the needs and requirements of the user, particularly ophthalmologists or opticians.

[0048] It is conceivable to provide the additional lens arrangement 22 permanently or detachably in or on the frame of the trial frame 30. The permanent arrangement has the advantage that incorrect lenses cannot be used. A detachable arrangement has the advantage that one and the same frame 30 can be used in measurement configurations with varying distance a or with a value adapted to the patient's interpupillary distance.

[0049] Figure 3a shows the front view of a phoropter 40 according to the invention; Figure 3bshows this in a side view. In this embodiment, it can be seen that the additional lens arrangement 22 is located in front of the phoropter 40, i.e. between the phoropter 40 and the optotype display 14. However, it is also conceivable to attach at least one additional lens arrangement 22 inside the phoropter 40 and / or behind the device. In this case, the respective phoropter 40 can meet the needs and requirements of the user. It is conceivable to provide the additional lens arrangement 22 permanently or detachably in or on the phoropter 40. The permanent arrangement has the advantage that no incorrect lenses can be used. A detachable arrangement has the advantage that one and the same phoropter 40 can be used in measuring constellations with varying distance a or with a value adapted to the patient's interpupillary distance.

[0050] In the Figure 4A device 10 according to the known prior art is shown in a schematic plan view, depicting both eyes 16 of a human person looking at the optotype display 14. Furthermore, the two fixation lines 50 are shown, each extending from the center of the pupil 18 of the respective eye 16 to an object point 51 present on the optotype display 14. Due to the finite distance a, the two fixation lines 50 converge toward the object point 51.

[0051] For example, with a pupillary distance PD of 66 mm, each eye has a pupillary distance PD R / L to an imaginary center line 54 of PD R / L = PD / 2 = 33 mm. At a distance a = 4 m to the optotype display, this results in a prismatic error of F p R / L = 0.825 cm / m per eye 16, where: F p R / L = PD R / L / a = 0 , 825 cm / m , or for both eyes 16: F p = PD / a = 1 , 65 cm / m .

[0052] In addition, the person then does not look vertically through the measuring device 12 or through its lenses, but past the center 62 of the measuring device 12, which results in image errors of these lenses increasing and indicating a visual impairment.

[0053] To remedy this, the device 20 according to the invention, as shown in Figure 5 As shown in a schematic plan view, a prism arrangement 40 is provided for each eye 16 on the side of the respective additional lens arrangement 22 facing away from the measuring device 12. The prism arrangements 40 at least largely compensate for the prismatic error F p . In the example mentioned, the prismatic error of F p R / L = 0.825 cm / m is therefore ideally completely compensated for each eye 16.

[0054] The respective additional lens arrangement 22 and the associated prism arrangement 40 can be accommodated in a common optical unit 60. The optical unit 60 can, as shown in the Figures 2 and 3shown, can be accommodated at different locations on the trial frame 30 or the phoropter 40.

[0055] The prism arrangements 40 are designed such that the light from the optotype display 14 or the object point 51 of the optotype display 14 falling into the respective observing eye 16 is deflected such that the fixation line 52 of the respective eye 16 runs through the center 62 of the measuring device 12. The fixation lines 52 of the two eyes 16 therefore ideally run perpendicular to the lens plane of the measuring device 12 and the additional device 22 and parallel to one another. The prism arrangements 40 provide a prismatic compensation p, which ensures an at least largely parallel position of the eyes 16, with the exit point of the light from the respective measuring device 12 being in the center 62 of the measuring device 12.

[0056] In the table according to Figure 6 (which in the Figure 6.1 and 6.2The first column shows the distance a from the eye 16 or pupil 18 to the optotype display 14 in meters. The next column shows the refractive error FR = 1 / a for the respective distance a without the provision of the additional lens arrangement 22 in dpt, and the next column shows the refractive power of four different additional lens arrangements in dpt, with the different lens arrangements each having a refractive power difference of 1 / 20 dpt. The fourth column shows the remaining, acceptable refractive error, i.e. the difference between the refractive error FR without the additional lens arrangement 22 and the refractive power b of the respective additional lens arrangement 22.

[0057] From this you can see that the refractive error FR for a distance a between 4 m and 10 m is in the range of 0.1-0.25 dpt and decreases with increasing distance. It has been shown that an additional lens arrangement is sufficient whose refractive power is rounded to the nearest 1 / 20 dpt. This means that for the range from 4 to 10 m only four different additional lens arrangements, i.e. additional lens arrangements with only four different refractive powers b, are required to sufficiently compensate for the refractive error FR: For a distance a of 4.00 m we need a first additional lens arrangement with a refractive power of 0.25 dpt. For a distance of 4.10 m to 5.10 m we need a second additional lens arrangement with a refractive power of 0.2 dpt. For a distance of 5.20 m to 6.90 m we need a third additional lens arrangement with a refractive power of 0.15 dpt.For a distance of 7.00 m to 10.00 m, a fourth additional lens arrangement is finally created with a refractive power of 0.1 dpt.

[0058] Consequently, all distances a between 4 and 10 meters can be covered with just four different additional lens arrangements, with the refractive error FR at a distance a of 4.10 m being reduced to a maximum of 0.044 D. Furthermore, it is conceivable to select finer lens graduations to achieve an even more precise result.

[0059] In the Figure 6 The following columns show the prismatic errors for each eye (F p R / L) at a pupil distance from the midline 54 of 26 mm, 28 mm, 31 mm, 33 mm, and 35 mm. Further to the right in the table, the prismatic error F p is shown for a pupil distance PD of the two pupils 18 of 52 mm, 46 mm, 62 mm, 66 mm, and 70 mm. The average value for men is 75 mm and for women 72 mm.

[0060] The prismatic error for both eyes 16 is calculated as follows: F p = PD / a.

[0061] In order to optimally compensate for the prismatic error depending on the pupil distance PD and the distance a, a prism compensator can be used.

[0062] In the event that no prism compensator is available, it is conceivable to provide four different prism arrangements 40 for each eye 16 in the range of a distance a of 4-10 m in order to remain within an acceptable tolerance. It has been shown that prism arrangements with a prismatic compensation p of 0.65 cm / m, 0.51 cm / m, 0.38 cm / m, or 0.26 cm / m are sufficient. Thus, for the range from 4 to 10 m, only four different prism arrangements are required to adequately compensate for the prismatic error: For a distance a of 4.00 m, a first prism arrangement per eye 16 results, the prismatic compensation p = 0.65 cm / m. For a distance of 4.10 m to 5.10 m, a second prism arrangement results, with a prismatic correction of p = 0.51 cm / m. For a distance of 5.20 m to 6.90 m, a third prism arrangement results per eye 16, with a prismatic correction of p = 0.38 cm / m.For a distance of 7.00 m to 10.00 m, a fourth prism arrangement per eye 16 is finally obtained, the prismatic compensation of which is p = 0.26 cm / m.

[0063] Optimally, four different optical units 60 can therefore be provided for a distance a between 4 m and 10 m, which can be arranged on or in the measuring device: A first optical unit is then used at a distance a of 4 m and has a lens arrangement with a refractive power of 0.25 dpt and a prism arrangement with a compensation of 0.65 cm / m. A second optical unit is then used at a distance a of 4.10 m to 5.10 m and has a lens arrangement with a refractive power of 0.2 dpt and a prism arrangement with a compensation of 0.51 cm / m. A third optical unit is used at a distance a of 5.20 m to 6.90 m and has a lens arrangement with a refractive power of 0.15 dpt and a prism arrangement with a compensation of 0.38 cm / m.A fourth optical unit is used at a distance a of 7.0 m to 10 m and has a lens arrangement with a refractive power of 0.1 dpt and a prism arrangement with a compensation of 0.26 cm / m.

[0064] Although the exemplary embodiment only addresses a distance a between 4 m and 10 m, the invention can also be used to achieve distances less than 4 m. The additional lens arrangement and the prism arrangement must then each be adapted to the smaller distance a.

[0065] By providing such optical units, a spherical and a prismatic compensation can be achieved, which ultimately leads to optimal measured values.

Claims

1. Apparatus (20) for testing visual acuity and / or for determining a refraction of at least one eye (16) of a patient, comprising a measuring device (12) in the form of a phoropter (40) or a trial frame (30), and comprising an optotype display (14), the measuring device (12) being located between the eyes (16) and the optotype display (14), at least one additional lens arrangement (22) being provided which refracts the light, incident in the relevant observing eye (16), from the optotype display (14) with a refractive power such that the observing eye (16) perceives a distance to the optotype display (14) that tends toward infinity, the apparatus (20) comprising at least one prism arrangement (40) which is designed to deflect the light of the optotype display (14), which light is incident in the relevant observing eye (16) of the patient whose visual acuity is being tested and / or measured, in such a way that the line of focus (52) of the relevant eye (16) of the patient runs at least largely through the center of the measuring device (12) and / or parallel to the line of focus (52) of the other eye (16) of the patient, characterized in that the additional lens arrangement (22) is arranged on the side of the measuring arrangement (12) facing the optotype display (14) and the prism arrangement (40) is arranged on the side of the additional lens arrangement (22) facing the optotype display (14).

2. Apparatus (20) according to claim 1, characterized in that the optotype display (14) is arranged at an actual distance a from the eyes (16) of the patient, whose visual acuity is being tested and / or measured, of at least 2 m, and preferably of 4 m to 10 m, from the eyes.

3. Apparatus (20) according to any of the preceding claims, characterized in that an additional lens arrangement (22) and a prism arrangement (40) are provided for each eye (16).

4. Apparatus (20) according to any of the preceding claims, characterized in that the prism arrangement is provided directly in front of, inside and / or directly behind the measuring device (12).

5. Apparatus (20) according to any of the preceding claims, characterized in that the additional lens arrangement (22) and / or the prism arrangement (40) are adjustable.

6. Apparatus (20) according to any of the preceding claims, characterized in that the additional lens arrangement (22) and / or the prism arrangement (40) is permanently detachably or non-detachably provided on the measuring device (12).

7. Apparatus (20) according to any of the preceding claims, characterized in that the additional lens arrangement (22) has a refractive power b for which the following applies: b = 1 / a or b = 1 / a + / - r, where r: rounding tolerance; a: actual distance from the optotype display (14) to the eyes (16) of the patient whose visual acuity is being tested and / or measured.

8. Apparatus (20) according to claim 7, characterized in that the rounding tolerance r is in the range of r = + / - 1 / 10 to + / - 1 / 30 diopter and more preferably 1 / 20 diopter.

9. Apparatus (20) according to any of claims 3 to 8, <b>characterized in that, for each eye (16) of the patient, the prism arrangement (40) achieves a prismatic compensation p for which the following applies: p = PDR / L / a or p = PDR / L / a + / - R, where PDR / L: half interpupillary distance of the eyes; R: rounding tolerance; a: actual distance from the optotype display (14) to the eyes (16) of the patient whose visual acuity is being tested and / or measured.

10. Apparatus (20) according to claim 9, characterized in that, - for each eye (16), the optical unit comprises an additional lens arrangement (22) having a refractive power b = 0.25 dpt, and a prism arrangement (40) having a prismatic compensation p = 0.65 cm / m; - for each eye (16), the optical unit comprises an additional lens arrangement (22) having a refractive power b = 0.2 dpt, and a prism arrangement (40) having a prismatic compensation p = 0.51 cm / m; - for each eye (16), the optical unit comprises an additional lens arrangement (22) having a refractive power = 0.15 dpt, and a prism arrangement (40) having a prismatic compensation p = 0.38 cm / m; or - for each eye (16), the optical unit comprises an additional lens arrangement (22) having a refractive power = 0.1 dpt, and a prism arrangement (40) having a prismatic compensation p = 0.26 cm / m.

11. Use of an apparatus (20) according to any of claims 1 to 10 for testing visual acuity and / or for determining a refraction.