Confocal refractometer for determining the refraction of a patient's eye

Abstract

Confocal refractometer for determining the refraction of a patient's eye (12), comprising a measuring light source (14) for generating a measuring light beam (16), a measuring module (18) having a light detector (20) for measuring the intensity of the measuring light, and further comprising optics (22) through which a measuring beam path is traversed to direct the measuring light beam (16) onto the retina (23) of the eye (12) and to direct back-reflected measuring light (24) from the retina (23) to the light detector (20), wherein the measuring beam path is confocal overall, wherein the optics (22) has an adaptive optical module (AOM), wherein by adjusting the adaptive optical module (AOM) a wavefront of the measuring beam path can be changed so that the intensity of the back-reflected measuring light (24) measured by the light detector (20) changes, wherein the measuring module (18) is designed to be used, based on an adjustment of the adaptive optical module (AOM),to determine the spherical equivalent (SE) of the ametropia of the eye (12) when the measured intensity of the back-reflected measuring light (24) is at a maximum, characterized in that the adaptive optical module (AOM) has an adaptive component (74; 94; 102; 118) which is designed to compensate for astigmatism in the wavefront of the measuring light by adjusting the adaptive component (74; 94; 102; 118), and wherein the measuring module (18) is designed to determine the astigmatism (C) of the eye and the axis (Δphgr;) of the astigmatism from a setting of the adaptive component (74; 94; 102; 118) when the measured intensity of the back-reflected measuring light (24) is at a maximum.

Description

The invention relates to a confocal refractometer for determining the refraction of a patient's eye, according to the preamble of claim 1. Such a confocal refractometer is known from US 2015 / 0109580 A1. Devices for determining the refraction of a patient's eye are known in the prior art, with which the spherical equivalent of ametropia, astigmatism, and the axis of astigmatism can be measured simultaneously. These devices have a wavefront sensor, for example, a Hartmann-Shack sensor, a Talbot-Moiré sensor, or the like. Such refractometers can include movable lens elements to reduce the curvature of the wavefront incident on the wavefront sensor, so that even eyes with high ametropia can be measured. Such a refractometer with a wavefront sensor is known from US 6,550,917 B1. This refractometer has movable optical components to reduce the curvature of the wavefront striking the sensor, depending on the ametropia of the patient's eye. Variable lenses can also be used as adaptive optical elements, which can be positioned in a plane conjugated to the surfaces of the eye. The confocal refractometer known from the above-mentioned document US 2015 / 0109580 A1 does not have a wavefront sensor, which is advantageous because wavefront sensors are sensitive to stray light, such as that caused by the cornea, the eye lens or lens surfaces, and wavefront sensors are also expensive optical components. However, a disadvantage of this known refractometer is that it only allows the measurement of the spherical equivalent of ametropia, but not the measurement of astigmatism and its axis. A quantitative determination of astigmatism and its corresponding axis is not possible with this known refractometer, even though the use of cylindrical lenses is mentioned. Furthermore, devices for optical coherence tomography (OCT) are known that can be used to perform measurements on a patient's eye, for example, to measure and visualize structures of the anterior chamber or retina in three dimensions. Such an OCT device typically comprises an interferometer with a reference arm and a measurement arm that extends to the area of ​​the eye being examined. This type of OCT device is described in the article by Y. Jian, J. Xu, MA Gradowski, S. Bonora, RJ Zawadzki, and MV Sarunic: "Wavefront sensorless adaptive optics optical coherence tomography for in vivo retinal imaging in mice," Biomedical Optics Express 2014, pages 547–559, DOI: 10.1364 / BOE.5.00547. In this OCT device, the fiber end of an optical fiber is imaged onto the retina of a mammalian eye.The measurement light scattered by the retina passes through the optics a second time and is coupled into the fiber end, which simultaneously acts as a confocal aperture. The device incorporates an adaptive mirror as an adaptive optical element, which compensates for aberrations of the eye under examination. The article further describes an algorithm for controlling the adaptive optical element so that the measurement light fed back into the fiber has the highest possible intensity. This OCT device is not a refractometer, however, but rather its purpose is to generate a high-quality OCT image of the retina. According to the article, the OCT image is of particularly good quality when the intensity of the light fed back into the fiber is high.This well-known OCT device is unsuitable for use as a refractometer for the following reasons: The adaptive mirror has a very small deflection of only 5 µm. This is clearly insufficient to compensate for corneal astigmatism and maximize the signal fed back into the fiber. To nevertheless maximize the signal amplitude, a contact lens is used, which is placed on the eye. This compensates for any astigmatism that may be present and produces a high-quality OCT image. However, the contact lens prevents the measurement of astigmatism, which is primarily caused by corneal asymmetry. Furthermore, the use of a contact lens is likely to affect the mean spherical refractive power of the cornea. Consequently, the spherical equivalent of ametropia cannot be measured with this setup.The use of a contact lens is a significant intervention and is uncomfortable for the patient, so its use should be avoided whenever possible. DE 10 2013 021 974 B3 discloses a device for determining the ametropia of an eye, comprising a measuring light source, beam shaping optics, and an analysis module with a detector and analysis optics. The detector is a spatially resolved detector, wherein the acute angle between a surface normal of the detection surface and the predetermined line is less than 80°. A control system is configured to obtain light intensity data detected by the detector and to derive ametropia data from the light intensity data, which represent the ametropia of the eye. US 2014 / 0176904 A1 discloses an ophthalmic aberrometer that combines measurements of wavefront aberrations and subjective refraction in a single instrument. EP 1 639 937 B1 discloses a device for measuring the refractive power of an eye. The invention is based on the objective of further developing a confocal refractometer of the type mentioned above in such a way that astigmatism and its axis position in the patient's eye can also be determined with minimal design effort. With regard to the aforementioned confocal refractometer, this problem is solved by the characterizing features of claim 1. The confocal refractometer according to the invention allows not only the measurement of ametropia but also of astigmatism and its axis for an examined patient eye. A measure of ametropia is the spherical equivalent (SE). Both the spherical equivalent (SE) and the astigmatism (C) are usually expressed in diopters (D). Eyes with a spherical equivalent (SE) < 0D are usually described as nearsighted or myopic, while eyes with SE > 0D are described as farsighted or hyperopic. Patient eyes with SE ≈ 0D are described as spherically normal or emmetropic. The astigmatism (C) indicates the difference in the refractive power of the eye in two perpendicular principal meridians. The axis (φ) specifies the position of these principal meridians, represents an angle, and is expressed in degrees (°).The refractometer according to the invention allows the measurement of the quantities SE, C and φ in a simple and accurate way without a wavefront sensor. The following convention is used in the description of the present invention: Astigmatism C is always positive and satisfies C > 0D. In the two principal meridians, the refractive error of the patient's eye is described by SE ± (1 / 2) C. The axis φ describes the position of the principal meridian with the refractive error SE + (1 / 2) C. With known values ​​of SE, C, and φ, a spectacle lens can be manufactured that corrects the refractive error of the patient's eye. Other conventions for describing the refractive error can also be used, but these can always be converted into the convention specified above. In the context of the present invention, a "confocal" optical system is understood to enable point-to-point imaging. A pinhole aperture illuminated by the light source with measuring light is imaged as a measuring light beam onto the retina of the patient's eye, thus creating a spot of light on the retina. The measuring light beam is focused onto the retina by a focusing device so that the spot of light on the retina can be kept as small as possible. Measuring light striking the area of ​​the spot of light is partially scattered by the retina, so that light energy exits the eye as back-reflected measuring light. A confocal aperture is positioned in a plane conjugate to the retina, which at least partially transmits the measuring light reflected from the eye. The intensity of the back-reflected measuring light transmitted by the aperture is measured by the measuring module with a light detector.Instead of a physical aperture, the end of an optical fiber can also be used as the confocal aperture on the light source side and as the confocal aperture on the light detector side. The confocal refractometer according to the invention does not require a wavefront sensor, which makes it insensitive to scattered light and also more cost-effective to manufacture. Instead, the quantities SE, C, and φ are measured by measuring the maximum intensity of the back-reflected measurement light using the light detector. The confocal refractometer according to the invention comprises an adaptive optical module that includes an adaptive component designed to compensate for astigmatism with any axis orientation in the wavefront of the measured light by adjusting the adaptive component. The adaptive optical module can have at least one movable optical element and / or at least one optical element whose optical properties, in particular its cylindrical refractive power, are variable. It is understood that the adaptive optical module can have several adaptive components, and also that the optics of the refractometer can have several adaptive optical modules. The adaptive optical module of the confocal refractometer according to the invention is adjustable to compensate for the spherical equivalent of the ametropia of the eye in the wavefront of the measuring light, and furthermore, the adaptive component of the adaptive optical module is designed to at least partially compensate for astigmatism with any axis orientation in the wavefront of the measuring light by adjustment. The measuring module of the confocal refractometer according to the invention is designed to determine the astigmatism of the eye and its axis position from a setting of the adaptive component in which the measured intensity of the back-reflected measuring light has a maximum. Preferably, the adaptive component can be adjusted to a neutral setting in which the adaptive component has no astigmatic effect. An advantage of this method is that, during the refraction determination of the patient's eye, an approximate measurement of the spherical equivalent can first be taken in the neutral setting of the adaptive component without having to remove the adaptive component from the measurement beam path, which further reduces the design effort. Subsequently, the axis of astigmatism can be measured by adjusting the adaptive component from the neutral setting. Preferably, the astigmatic effect of the adaptive component is continuously adjustable. An advantageously simple design of the adaptive component can be achieved by having the adaptive component have two cylindrical lenses that can be rotated relative to each other, one of which has a positive refractive power and the other of which has a negative refractive power, wherein the positive and the negative refractive power are equal in magnitude. In this configuration of the adaptive component, it can be set to a neutral position as described above, in which the adaptive component has no astigmatic effect, since the positive and negative refractive powers of equal magnitude cancel each other out, and by rotating the cylindrical lenses from the neutral position relative to each other, an astigmatic effect can then be set that compensates for the astigmatism of the patient's eye. The adaptive component can advantageously also have two plates, each having a surface contour, wherein the two surface contours are complementary to each other, and wherein the plates are translationally displaceable and / or rotatable relative to each other. Such an optical component is also known as an Alvarez plate. With such an adaptive component, an astigmatic effect can also be adjusted with different axis positions, starting from a neutral setting in which the adaptive component exhibits no astigmatic effect. The adaptive component can also include one or more fluid-filled lenses whose spherical and / or astigmatic refractive power can be changed. It can advantageously be provided that the adaptive component has two cylindrical lenses which are crossed at an angle other than 0° to each other, wherein the cylindrical lenses are in particular fixed in position to each other, and wherein the refractive power of the cylindrical lenses is variable. The two cylindrical lenses are crossed at an angle of 45° to each other. Both cylindrical lenses have a variable refractive power. As with the previously mentioned configurations, the astigmatism and axis of this combination of cylindrical lenses can be continuously varied by appropriately selecting the astigmatic refractive powers of the two individual cylindrical lenses. This provides an adaptive component that requires no mechanical movement to adjust the astigmatism and axis of the patient's eye. It is further preferred that the adaptive component in the measuring beam path is positioned in a plane that is conjugate to a pupil of the eye. The advantage here is that the adaptive component allows astigmatism and its axis position in the wavefront of the measuring light to be compensated for independently of any spherical refractive error of the patient's eye. In the sense of a confocal arrangement, a first pinhole aperture can be located near the measuring light source and a second pinhole aperture can be located near the light detector, with the first and the second pinhole aperture being confocal, as already described above. As an alternative to a refractometer design with pinhole apertures, the measuring light source can be connected to a first optical fiber and the light detector to a second optical fiber, wherein the first and the second optical fibers are connected to or transition into a third optical fiber via a fiber coupler, with a free end of the third optical fiber forming a confocal exit end for the measuring light beam and a confocal entry end for the back-reflected measuring light. The free end of the optical fiber thus takes on the function of two confocal apertures. This has the advantage of further simplifying the design of the refractometer, as no apertures are required within the refractometer itself; instead, confocality is achieved via a single optical fiber end. In connection with the aforementioned measure, it is further advantageous if a lock-in amplifier, in particular a chopper wheel, is arranged in the measuring beam path. With the aid of the lock-in amplifier, in particular a rapidly rotating chopper wheel, the light path between the optical fiber and the eye is blocked and released at a high frequency. Any background signal that may be present can then be eliminated from the modulation of the light detector signal. This background signal can arise, for example, when light from the measuring light source is coupled directly towards the light detector in the fiber coupler without passing through the measuring beam path. In a further preferred embodiment, a deflecting element can be arranged in the measuring beam path, which periodically deflects the measuring light beam, such that the measuring light beam is periodically moved on the retina of the eye. This measure has the advantage that the influence of speckle effects or retinal inhomogeneities can be suppressed or at least reduced. Here, the light spot on the retina is preferably moved at high speed over short distances. This allows for averaging over different signal levels that arise due to retinal inhomogeneities or speckle effects. The deflection element can, for example, be a tilted, rotatable planoplate in a non-parallel beam path. Alternatively, other methods for variable beam deflection can be used, such as scanning mirrors, as employed in OCT systems. In a further preferred embodiment, the optics in the measuring beam path, for example viewed from the patient's eye behind the adaptive optical module, have a beam splitter to which a display and / or an image sensor is assigned, wherein the display and / or the image sensor is preferably arranged on an optical axis that passes through the eye and the adaptive optical module. The beam splitter allows the patient to, for example, view a display. A display can be advantageously used to provide the patient with an incentive to align their eye axis along an optical axis of the refractometer or to encourage accommodation. Such a display can also be used for subjective refraction measurement, where the adaptive optical module acts as a phoropter. An image sensor can be used to capture an image of the anterior segment of the patient's eye and to verify that the patient's eye is in a suitable position relative to the refractometer. In advantageous embodiments, the adaptive optical module can comprise an optical fiber, a first lens group, the adaptive component and a second lens group, wherein the adaptive component is arranged near the focal plane of the second lens group. The optics can advantageously include a third lens group, which, for example, is arranged behind the second lens group when viewed from the measuring light source, wherein the third lens group is arranged such that the pupil of the eye is located near a focal plane of the third lens group. Preferably, the optical fiber, the first lens group, the adaptive component and the second lens group are jointly movable in the direction of the measuring beam path relative to the third lens group. The aforementioned optical elements can thus be arranged together on a movable carriage, while the aforementioned optical elements can be fixed in position relative to each other, thereby keeping the control effort and the number of moving parts low. In another advantageous embodiment of the adaptive optical module, it can have a first lens group, a second lens group and the adaptive component, wherein the first lens group is movable along the measuring beam path relative to the second lens group. The optics of the refractometer can further comprise an optical fiber, a third lens group and the adaptive optical module, wherein the optical fiber and the first lens group are preferably stationary. In this configuration, the optical fiber, whose exit end is imaged onto the retina of the patient's eye, is advantageously not movable, but stationary. In a further embodiment of the adaptive optical module, it can have a first lens group and the adaptive component, wherein the first lens group is movable in the direction of the measuring beam path relative to the at least one adaptive optical element. In a design that requires very few optical elements, the adaptive optical module comprises an optical fiber, a first folding mirror, a lens group, a second folding mirror and the adaptive component. In this case, the adaptive optical module can advantageously represent the entire optics of the refractometer; that is, the refractometer's optics consist solely of the adaptive optical module. Here, the adaptive optical module can advantageously serve as a monocular phoropter. By providing two parallel modules, a binocular phoropter can also be implemented. At least one of the folding mirrors can advantageously be movable to move the measuring light beam on the retina, as already described above, in order to suppress the influence of speckle effects or inhomogeneities of the retina. To compensate for the spherical equivalent of the ametropia of the patient's eye, the optical fiber is preferably movable in the direction of the measuring beam path relative to the first folding mirror. Overall, the aforementioned design results in a very cost-effective refractometer. In another preferred embodiment, the adaptive optical module can be designed to compensate for aberrations of a higher order than the basic order of astigmatism in the wavefront. Higher-order aberrations are defined as aberrations that cannot be described by the three Zernike functions for defocus and astigmatism. For example, this configuration allows image aberrations such as coma, trile leaf aberration, etc., to be compensated for and measured. An adaptive mirror or a liquid crystal-based spatial light modulator can be used as an adaptive component of the adaptive optical module for this purpose. The higher-order aberrations of the eye can then be read out or derived by the measuring module from the setting of the adaptive optical module at which the intensity detected by the light detector is at its maximum. The refractometer according to the invention can further advantageously include a control unit for adjusting the adaptive optical module. The control unit can be configured, particularly in conjunction with the measuring module, to adjust the adaptive optical module so that the intensity of the back-reflected measuring light measured at the light detector has a maximum. The control unit can be fully automated; in particular, feedback can be provided between the measurement light intensity detected by the light detector and the control unit, whereby the control unit adjusts the adaptive optical module until the intensity of the back-reflected measurement light measured at the light detector reaches a maximum. The control unit can advantageously be configured to adjust the adaptive optical module initially during a neutral setting of the adaptive component, in which the adaptive component has no astigmatic effect, until the intensity measured at the light detector reaches a maximum. If a first and second maximum are detected at the light detector due to existing astigmatism of the patient's eye, the measuring module can advantageously determine the spherical equivalent from the respective setting of the adaptive optical module, and the astigmatism can be determined at least approximately from the two maxima. Furthermore, the measuring module can be configured to determine the spherical equivalent from the setting of the adaptive optical module when only a maximum is detected at the light detector, and to determine the astigmatism as at least approximately 0. Furthermore, the control unit is advantageously configured to adjust the adaptive component from the neutral setting so that the adaptive component compensates for the astigmatism regardless of its axis position, and to further adjust the adaptive component until the intensity detected at the light detector no longer increases, wherein the measuring module is configured to determine the axis position of the astigmatism from the resulting setting of the adaptive component. The aforementioned algorithms for determining the spherical equivalent of ametropy, astigmatism and its axis position can advantageously be stored as a computer program in the control unit and / or the measuring module. The invention also relates to an OCT device for optical coherence tomography examination of a patient's eye, which has an integrated refractometer according to one or more of the aforementioned embodiments, wherein the measuring light source is formed by an OCT light source, and wherein an OCT beam path at least partially penetrates the optics of the refractometer. In this configuration, a combined device with OCT functionality and refraction measurement is advantageously created. The OCT light source is advantageously used as the measuring light source for refraction measurement, so that only one light source is required for both functions. The scan mirrors present in an OCT device can advantageously be used to spatially vary the light spot on the retina and thus eliminate undesirable effects of retinal inhomogeneities and speckles, as described above. Additionally, combining the OCT device with a refractometer according to the invention improves OCT image quality, since astigmatism of the patient's eye can be compensated for and thus eliminated by the adaptive component of the adaptive optical module, resulting in increased lateral resolution of the retina in the OCT image. Furthermore, in this device combination, the OCT system can be used to determine whether the patient's eye is correctly rotated. In this case, the OCT system scans the retina in the area of ​​the fovea, the region of sharpest vision. The refraction measurement can then be triggered once it has been confirmed that the patient's eye is correctly rotated. Alternatively, it can simultaneously be required that the patient's pupil is in the correct position, which is possible with the image sensor mentioned above. The refraction measurement is then triggered when the OCT light beam scans the fovea and the patient's pupil is in the correct position. However, the refractometer according to the invention can also be designed as an autonomous device, in particular as a table-top device. The invention also relates to a method for determining the refraction of a patient's eye, comprising the steps of: providing a confocal measuring beam path in which an adaptive optical module is arranged, which is designed to compensate for a spherical equivalent of the eye's ametropia in the wavefront of the measuring beam path by adjustment, and which has an adaptive component designed to compensate for astigmatism in the wavefront of the measuring beam path by adjustment; directing a measuring light beam onto the eye such that a spot of light is produced on the retina of the eye; measuring the intensity of the measuring light reflected back from the retina; adjusting the adaptive optical module and the adaptive component until the measured intensity is maximal;Determine, from the setting of the adaptive optical module and the adaptive component at which the measured intensity is maximal, the spherical equivalent, the astigmatism and its axis position. The method according to the invention has the same advantages and the same preferred embodiments as the refractometer according to the invention. Further advantages and features will become apparent from the following description and the accompanying drawings. It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the present invention. Exemplary embodiments of the invention are illustrated in the drawing and are described in more detail below with reference to them. The figures show: Fig. 1 a schematic diagram of a confocal refractometer according to a first embodiment; Fig. 2 a schematic diagram of a confocal refractometer according to a further embodiment; Fig. 3 a schematic diagram of a confocal refractometer according to yet another embodiment; Fig. 4 a schematic diagram of a confocal refractometer according to yet another embodiment; Fig. 5 a confocal refractometer for determining the refraction in different settings of an adaptive optical module of the refractometer for determining different refractive errors of patient eyes; Fig. 6 measured intensities of back-reflected measuring light for different astigmatism-free patient eyes with different spherical equivalents of ametropia; Fig.7. Measured intensities of back-reflected measuring light at various astigmatisms for a value of the spherical equivalent of ametropia; Fig. 8. A flowchart illustrating a method for determining the refractive error of a patient's eye; Fig. 9. Another embodiment of a confocal refractometer in various settings of the adaptive optical module for different refractive errors of patient eyes; Fig. 10. Yet another embodiment of a confocal refractometer in various settings of the adaptive optical module for different refractive errors of patient eyes; Fig. 11. Yet another embodiment of a confocal refractometer in various settings of the adaptive optical module for different refractive errors of patient eyes; Fig. 12. A schematic diagram of a confocal refractometer in combination with an OCT system. Fig. 1 shows a confocal refractometer, designated with the general reference numeral 10, for determining the refraction of one eye 12 of a patient. The refractometer 10 has a measuring light source 14 for generating a measuring light beam 16. The measuring light beam is indicated by dashed lines in Fig. 1. The refractometer 10 also has a measuring module 18, which includes a light detector 20 for measuring the intensity of back-reflected measuring light 24, indicated by solid lines in Fig. 1. The refractometer 10 has optics 22 through which a measuring beam path is traversed, in order to direct the measuring light beam 16 onto the retina 23 of the eye 12 and to supply the measuring light 24 reflected from the retina 23 to the light detector 20. The measuring beam path is understood to be the entirety of the measuring light beam 16 and the back-reflected measuring light 24. The measuring beam path is confocal overall. In the context of the refractometer 10, "confocal" means that the measuring light source 14, more precisely a confocal aperture 26 provided as an opening in a pinhole 27, is imaged onto the retina 23, so that the smallest possible light spot 28 is generated on the retina. Light striking the area of ​​the light spot 28 is partially scattered by the retina 23, so that light energy exits the eye 12 as back-reflected measuring light. A confocal aperture 30, provided as the opening of a pinhole 31, is located in a plane conjugate to the retina 23 and allows at least some of the back-reflected measuring light exiting the eye 12 to pass through. The intensity of the back-reflected measuring light 24 behind the confocal aperture 30 is measured by the light detector 20.The aperture 26, which is assigned to the measuring light source, is focused by the optics 22 onto the retina 23, so that the light spot 28 on the retina 23 can be chosen to be as small as possible. As shown in Fig. 1, the optics 22 further comprises a lens group 32 with which the measuring light beam coming from the aperture 26 is approximately collimated. The collimated measuring light beam 16 is guided via two beam splitters 34 and 36 into an adaptive optical module AOM. As will be described in more detail below, the module AOM contains one or more adaptive components, but can also generally contain optical components such as lenses, diffractive optical elements, mirrors, beam splitters, etc., which may also be arranged to be displaceable. For the purposes of this description, a “lens group” refers to either a single lens or, as shown in Fig. 1, an arrangement of several lenses, which may also have an air gap between the individual lenses. The AOM module is adjustable via a control unit 38. Depending on the setting of the AOM module, the wavefront of the measuring light beam 16 incident on the AOM module is modified. The measuring light beam 16 subsequently entering the eye 12 generates, as described above, a more or less large spot of light 28 on the retina 23 of the eye 12. In the area of ​​the spot of light 28 on the retina 23, the incident measuring light is scattered. A portion of the scattered light exits the eye 12 as back-reflected measuring light 24. The back-reflected measuring light 24 passes through the AOM module in the opposite direction and is guided as an approximately collimated light beam via the beam splitter 36 and the beam splitter 34 to the confocal aperture 30. Another lens group 33 focuses the back-reflected measuring light 24 onto the aperture 30. The light detector 20 behind the aperture 30 measures the intensity or power of the back-reflected measuring light 24 passing through the aperture 30. The control unit 38 contains, for example, a processing unit that uses a suitable algorithm to control the AOM module so that maximum power is measured at the light detector 20. The measuring module 18 can then determine the refraction of the eye 12 based on the setting of the AOM module at which the measured intensity of the back-reflected measuring light 24 is at its maximum, in particular the spherical equivalent of the ametropia, the astigmatism, and the axis of the astigmatism, as will be described in more detail later. It is understood that further optical components may be positioned between eye 12 and module AOM. The optics 22 can, as shown in Fig. 1, have the steel divider 36 in the measuring beam path, which is only optional in this respect, followed by a display and / or image sensor 40, wherein the display 40 and / or the image sensor 40 is / are arranged on an optical axis OA that passes through the eye 12 and the module AOM. A converging lens group 42 is arranged between the beam splitter 36 and the display and / or image sensor 40. The display 40 can be used to provide the patient with an incentive to align the eye axis along the optical axis OA of the refractometer 10, or to provide the patient with an incentive to accommodate. The display 40 can also be used for subjective refraction measurement by using the AOM module as a phoropter. The image sensor 40 can be used to capture an image of the anterior region of the eye 12 and to check whether the eye 12 is in a suitable position relative to the refractometer 10 according to the invention. It is understood that the measuring module 18 and the control unit 38 can be designed as a functional unit, whereby the function of the measuring module 18 can also be performed by the control unit 38 and vice versa. Fig. 2 shows a modification of the confocal refractometer 10. For elements of the refractometer 10 in Fig. 2 that are identical, similar, or comparable to elements of the refractometer 10 in Fig. 1, the same reference numerals are used as in Fig. 1. In the refractometer 10 shown in Fig. 2, the measuring light source 14 is connected to a first optical fiber 44, and the light detector 20 is connected to a second optical fiber 46. The first optical fiber 44 and the second optical fiber 46 are connected to, or transition into, a third optical fiber 50 via a fiber coupler 48. A free end 52 of the third optical fiber 50 forms an exit end for the measuring light beam 16 and an entry end for the back-reflected measuring light 24. In this embodiment, the confocality of the refractometer 10 is achieved by the free end 52 of the optical fiber 50 simultaneously acting as a confocal aperture, thus replacing the two confocal apertures 30 and 26 of the refractometer 10 shown in Fig. 1. In this embodiment, the beam splitter 34 shown in Fig. 1 can also be omitted, as shown in Fig. 2. Furthermore, reference can be made to the description of the refractometer 10 in Fig. Fig. 3 shows a further modification of the confocal refractometer 10 compared to the embodiment of the confocal refractometer 10 in Fig. 2. For the refractometer 10 in Fig. 3, the same reference numerals are used for elements that are identical, similar or comparable to elements of the refractometer 10 in Fig. 1 or Fig. 2 as in Fig. 1 or 2. In the refractometer 10 shown in Fig. 3, a lock-in amplifier 54 is arranged in the optics 22 of the refractometer 10 to increase the signal-to-noise ratio of the intensity of the back-reflected measuring light 24 measured by the light detector 20. The lock-in amplifier has a chopper wheel 56 which can be driven into rotation at high speed by a motor 58. The rapidly rotating chopper wheel blocks and releases the measuring beam path between the fiber 50 and the eye 12 at high frequency. This results in a modulation of the signal at the light detector 20, from which any background signal that may be present can be eliminated. This background signal can arise, for example, if measuring light from the measuring light source 14 in the fiber coupler 48 is coupled directly into the light detector 20.The control unit 38 is connected to the motor 58, so that the motor 58 and thus the rotational speed of the chopper wheel 56 can be controlled via the control unit 38. Fig. 4 shows a further modification of the confocal refractometer in Fig. 2. For the refractometer 10 in Fig. 4, the same reference numerals are used for elements that are identical, similar, or comparable to elements of the refractometer 10 in Fig. 1, Fig. 2, or Fig. 3 as in Fig. 1, Fig. 2, or Fig. 3, respectively. In the refractometer 10 in Fig. 4, a deflection element 60 is arranged in the measuring beam path, which serves to move the light spot 28 on the retina 23 of the eye 12 by small distances, as indicated by an arrow 62. The deflection element 60 can be designed in the form of a flat plate 64, which is inclined in the measuring beam path and arranged in the non-parallel measuring beam path, as shown in Fig. 4. The planar plate 64 is set into rotation by a motor 66, which leads to a periodic movement of the light spot 28 on the retina 23 of the eye 12.As an alternative to a tilted flat plate that is rotated by a motor, other types of variable beam deflection can also be used, such as scanning mirrors. In each of the confocal refractometers 10 according to Figs. 1, 2, 3 to 4, the respective optics 22 has an adaptive optical module AOM. The adaptive optical module AOM is designed to compensate for spherical refractive errors of the eye 12 by, for example, changing air gaps within the adaptive optical module or air gaps between the adaptive optical module and other optical elements of the optics 22, so that different curvatures of the wavefront of the measuring light beam incident on the eye 12 can be generated at the pupil P of the eye 12. Furthermore, such an adaptive optical module AOM is designed not only to compensate for the spherical equivalent of the ametropia of the eye 12, but also for astigmatism at any axis orientation of the astigmatism. For this purpose, the adaptive optical module has one or more adaptive components designed to...The adaptive component is used to compensate for astigmatism in the wavefront of the measuring light. The measuring module 18 is then designed to determine the astigmatism of the eye and the axis of the astigmatism from a setting of the adaptive component in which the measured intensity of the back-reflected measuring light 24, as measured by the light detector 20, has a maximum. The confocal refractometers 10 shown in Figs. 1, 2, 3 to 4 can be used to measure the spherical equivalent (SE), the astigmatism (C), and the axis φ of the astigmatism of the examined eye 12. The spherical equivalent (SE) is a measure of ametropia. Both the spherical equivalent (SE) and the astigmatism (C) are usually expressed in diopters (D). Eyes with a spherical equivalent (SE) < 0D are usually described as nearsighted or myopic, while eyes with SE > 0D are described as farsighted or hyperopic. Patient eyes with SE ≈ 0D are described as spherically normal or emmetropic. The astigmatism (C) indicates the difference in the refractive power of the eye 12 in two perpendicular principal meridians. The axis position φ specifies the position of these principal sections, represents an angle and is given in the unit degrees (°). The following convention is used in this description. Astigmatism C is always positive and satisfies C > 0D. In the two principal meridians, the refractive error of the patient's eye is described by SE ± (1 / 2) C. The axis φ describes the position of the principal meridian with the refractive error SE + (1 / 2) C. If SE, C, and φ are known, a spectacle lens can be manufactured to correct the refractive error of the patient's eye. It is understood that other conventions can also be used to describe the refractive error, but these can always be converted into the conventions given above. Examples of adaptive components that can compensate for astigmatism and its axis position include Stokes lenses, Alvarez lenses, liquid-filled lenses, etc., as described below. Stokes lenses have two cylindrical lenses that can be rotated relative to each other. One cylindrical lens has a positive refractive power Ccylinder, and the other has an equal but opposite negative refractive power -cylinder. If one of the cylindrical lenses is rotated by an angle θ and the other by an angle -θ, the resulting cylindrical refractive power is given by CSL = 2cylinder · sin(20). Thus, a Stokes lens allows for the generation of a continuously adjustable cylindrical refractive power CSL. If both cylindrical lenses are rotated together, the axis position can be varied. Such Stokes lenses can be used in the adaptive optical module AOM of the refractometer 10, as described below. An Alvarez lens has two plates, each with a surface contour that is complementary to each other, and the plates are translationally displaceable and / or rotatable relative to each other. The refractive power and / or astigmatism of an Alvarez lens can be continuously adjusted by positioning the plates accordingly relative to each other. In liquid-filled lenses, the spherical and / or astigmatic refractive power is variable. For example, two liquid-filled cylindrical lenses, each with a variable refractive power, can be used for the AOM module. These lenses are crossed at an angle other than 0°, for example, 45°. The cylindrical lenses are fixed in position relative to each other, and the astigmatism and axis of this combination of cylindrical lenses can be continuously varied by appropriately adjusting the astigmatic refractive powers of the two individual cylindrical lenses. In this configuration, the adaptive component of the AOM module can be varied with respect to its astigmatic effect, including its axis, without requiring any mechanical movement of the adaptive component. Regardless of the specific design of the adaptive component of the adaptive optical module (AOM), the adaptive component can be adjusted to a neutral setting in which it exhibits no astigmatic effect. Such a neutral setting is achieved in the examples described above, such as a Stokes lens, an Alvarez plate, or liquid-filled lenses. Fig. 5 shows an embodiment of an optic 22 with an adaptive optical module AOM, wherein the optic 22 can be used in the refractometer 10 according to Figs. 2, 3 to 4. In Fig. 5 only the confocal optic 22 of the refractometer is shown, while the other components such as the measuring light source, light detector, measuring module and control unit have been omitted for the sake of clarity. In the embodiment shown in Fig. 5, a single-mode fiber is used for the optical fiber 50 (see Fig. 2), with an aperture NA = 0.11 as an example. The wavelength λ of the measuring light generated by the measuring light source 14 (see Fig. 2) is, for example, 840 mm. At the free end 52 of the optical fiber 50, the waist radius w0 of the light emerging from the optical fiber 50 is, for example, 2.5 µm. However, instead of a single-mode fiber, a multimode fiber with a higher aperture and a larger constriction (waist) of the measuring light beam at the end 52 of the optical fiber 50 could just as easily be used. In Fig. 5, ellipses on the right edge of the image show schematic patient eyes with spherical equivalents between SE = - 10D (bottom) and SE = + 10D (top). The optical fiber 50 and thus the end 52 of the optical fiber 50 is movable in the direction of a double arrow 70, i.e. in the direction of the measuring light beam path or the optical axis. The end 52 of the optical fiber 50 is located near a focal plane of a first lens group 72, which collimates the measuring light beam emerging from the end 52 of the optical fiber 50. The focal length of the lens group 72 is, for example, 40 mm. Following the lens group 72 is an adaptive component 74, which is, for example, a Stokes lens having cylindrical lenses with a cylindrical refractive power Ccylinder = ± 1 D. The adaptive component 74 is arranged near a focal plane of a lens group 76, which has, for example, a focal length f76 of 150 mm. A further lens group 78 is arranged such that the pupil P of the eye 12 is located near the focal plane of the lens group 78. The lens group 78 has, for example, a focal length f78 of 60 mm. The lens groups 76 and 78 form, for example, a Keplerian telescope. In this embodiment, the end 52 of the optical fiber 50, the lens group 72, the adaptive component 74, and the lens group 76 form the adaptive optical module AOM, which is suitable for compensating spherical refractive errors, astigmatism, and their axial position. The entire module AOM can be moved along the optical axis according to a double arrow 80, for example, by mounting the module AOM on a carriage, so that the distance from the module AOM to the lens group 78 can be changed. The respective position of the module AOM can be specified by a distance d between the lens groups 76 and 78. The end 52 of the optical fiber 50, the lens group 72, the adaptive component 74, and the lens group 76 are fixed in position relative to each other in the direction of the optical axis (arrow 80). In the case of the adaptive component 74 being configured as a Stokes lens, the two associated cylindrical lenses are rotatable relative to each other about the optical axis. The measuring light beam exiting the end 52 of the optical fiber 50 is collimated by the lens group 72, passes through the adaptive component (Stokes lens) 74 as well as the lens groups 76 and 78, and enters the patient's eye 12 through the pupil P, where it creates a light spot 28 on the retina 23. The light scattered at the light spot 28 Light partially exits the eye 12 as back-reflected measuring light, passes through the optics 22 in reverse order, and is focused by the first lens group 72 onto the end 52 of the optical fiber 50, where it is partially coupled into the optical fiber 50, passes through the fiber coupler 48 (see Fig. 2), and the intensity of the back-reflected measuring light reaching the light detector 20 is measured by the light detector 20 (see Fig. 2). The AOM module is then moved according to arrow 80, and the adaptive component 74 is adjusted so that a maximum intensity is measured at the light detector 20. As will be described later, the spherical equivalent SE, as well as the astigmatism C and the associated axis position φ of the eye 12 can be determined from the position of the slide of the module AOM and the setting of the adaptive component 74 (Stokes lens) at which the intensity I of the back-reflected measuring light measured by the light detector 20 is at its maximum. In a position of the module AOM where the focal points of lens groups 76 and 78 coincide, the corresponding distance d between lens groups 76 and 78 is subsequently denoted as dafok. The distance dafok is approximately given by dafok ≈ f76 + f78 = 150 mm + 60 mm = 210 mm. A more precise determination of dafok for given lens groups 76 and 78 is possible both computationally and experimentally. A special property of the optics 22 of the embodiment in Fig. 5 results from the fact that the adaptive component 74 is arranged approximately in the focal plane of the lens group 76, and that the pupil P of the eye 12 is arranged near the focal plane of the lens group 78. In this arrangement, the adaptive component 74 and the pupil P are located in conjugate planes, and the magnification β between these conjugate planes is independent of the selected distance d: The following describes, also with reference to Fig. 8, how the refraction of the eye 12 can be determined or measured using the refractometer 10 in Fig. 5. In a first step S1, the intensity I of the back-reflected measuring light is measured as a function of the distance d between lens groups 76 and 78. During this measurement, the adaptive component 74 is adjusted so that it has no astigmatic effect. The astigmatism C74 produced by the adaptive component 74 is therefore 0D. In the case of a Stokes lens with two cylindrical lenses with opposite refractive powers that can be rotated relative to each other, the Stokes lens is adjusted accordingly so that the angle between the two cylindrical axes of the Stokes lens is 0° (θ = 0°). Fig. 6 shows exemplary measurements of intensity I for various astigmatism-free patient eyes with different spherical equivalents SE. The abscissa of the diagram in Fig. 6 shows the difference between the set distance d and the distance dafo, and the ordinate shows the corresponding intensity. From the distance d at which the measured intensity I reaches its maximum, the spherical equivalent SE can in this case be calculated using the equation: The distance d thus changes linearly with the spherical equivalent SE of the eye 12. Fig. 7 shows an example of the measured intensity I when the eye 12 is characterized by varying degrees of astigmatism C at the same spherical equivalent SE = +5D. While in the astigmatism-free case with C = 0D the measurement curve exhibits only one maximum, in the case of C > 0D two maxima occur. These two maxima of intensity I arise when the end 52 of the optical fiber 50 is focused onto the retina 23 in one of the two principal meridians. Since an eye 12 with astigmatism has a different refractive power in the two principal meridians, there are two distances d1 and d2 with d1 < d2 for which the intensity I is maximal. If the eye 12 exhibits only slight astigmatism, it can happen that the two maxima merge and only a broadened maximum can be resolved. In this case, the two distances d1 and d2 are identical.The distance Δ = d2- d1 between the maxima can be calculated using the following equation: Thus, by measuring the intensity I, determining the distance Δ, and applying equation (3), the astigmatism C of the eye can be approximately determined. In the case of an eye with astigmatism, the spherical equivalent SE is then determined according to: The spherical equivalent SE and the astigmatism C of the patient's eye are now approximately known. However, no statement can yet be made about the axis position φ. In the next step S2, the axis position φ is therefore determined. To determine the axis position φ, the distance d is first adjusted so that the previously determined spherical equivalent SE is compensated. Furthermore, the cylindrical refractive power Ccylinder of the adaptive component 74 is adjusted so that the previously determined astigmatism C of the eye 12 is equal to the astigmatism of the refractometer 10. This is achieved when the magnification β is calculated according to equation (1), and the refractive power Ccylinder is the refractive power of the cylindrical lenses of the adaptive component 74 in the case of a Stokes lens. Thus, the measuring light exiting the refractometer 10 exhibits approximately the same astigmatism as the eye 12, although the axis position φ still needs to be determined.If the astigmatism C was determined to be approximately C = 0D in the step above, a small value for the astigmatism is nevertheless set at the adaptive component 74 during step S2, which corresponds, for example, to C = 0.1D, C = 0.2D or C = 0.5D. The adaptive component 74, in the form of the Stokes lens, is now rotated around the optical axis while maintaining the angle θ. The rotation angle is denoted by φ74. The intensity I is measured as a function of the rotation angle φ74 in the range between 0° and 180°. In an eye 12 with astigmatism, the intensity I has a distinct maximum at the rotation angle φ74max. The maximum is more pronounced the greater the astigmatism C of the eye. The axis φ of the astigmatism of eye 12 can be determined from the rotation angle φ74max. If the astigmatism of eye 12 is small, the measured intensity I does not depend on the rotation angle φ74, and the refractive error of the patient's eye is sufficiently characterized by the spherical equivalent SE from step S1 as well as an astigmatism C = 0D, where in an astigmatism-free eye the axis position φ is arbitrary and can be specified, for example, as φ = 0°. In an optional step S3, the compensation values ​​for the spherical equivalent SE, the astigmatism C, and the axis φ, determined on refractometer 10 in steps S1 and S2, are adjusted by setting the distance d = (d2 - d1) / 2 between lens groups 76 and 78, the rotation angle θ between the cylindrical lenses of the Stokes lens of the adaptive component, and the rotation angle φ74max on the refractometer. The measured intensity I is then increased further by varying these parameters d, θ, and φ74max until this is no longer possible. As described in steps S1 and S2, the parameters SE, C, and φ that characterize the eye are then determined from the values ​​of the AOM module settings. Figure 8 summarizes the above-described method with steps S1, S2, and S3 in the form of a flowchart. It is understood that the method according to Figure 8 can be carried out not only with the embodiment of the refractometer 10 shown in Figure 5, but also with refractometers 10 in other configurations, as described below. The procedure in Fig. 8 includes additional steps S10 and S20. In step S10, it is first checked whether approximate values ​​for SE and C are known. If so, step S1 can be skipped, and the procedure continues with step S20. In step S20, it is checked whether an approximate value for the axis position φ is known. If so, step S2 can be skipped, and the procedure continues with the optional step S3. If the check in step S10 indicates that no approximate value for SE and C is known, step S1 is executed. Likewise, step S2 is executed if the check in step S20 indicates that no approximate value for the axis position φ is known. Fig. 9 shows another embodiment of a refractometer 10 with an optic 22 which, starting from an end 52 of an optical fiber 50, comprises an adaptive optical module AOM, an optional folding mirror 84, a beam splitter 36, such as the beam splitter 36 in Figs. 1, 2, 3 to 4 (optionally with a display and / or image sensor arranged behind it as described with reference to Fig. 1), and a lens group 86. The end 52 of the optical fiber 50, which supplies the measuring light beam, is located at the focal point of a lens group 88, which approximately collimates the measuring light beam. The adaptive optical module AOM comprises a lens group 90, which acts as a focusing lens, a lens group 92, and an adaptive component 94, which can be configured as a Stokes lens. The optical fiber 50 can be a single-mode fiber, for example with an aperture NA of 0.11.The wavelength λ of the measuring light is, for example, 550 nm, and the measuring light beam at the end 52 of the optical fiber 50 has, for example, a waist radius w0 of 1.6 µm. However, instead of a single-mode fiber, a multimode fiber could just as easily be used as optical fiber 50. The ellipses on the right edge of Fig. 9 schematically show eyes 12 with spherical equivalents SE = + 14D (top), SE = 0D (middle) and SE = - 17D (bottom). The lens group 88, for example, has a focal length of 9.84 mm. The lens group 86 focuses the pupil of the eye 12 in the vicinity of the adaptive component 94, the adaptive component 94 serving to compensate for the astigmatism C and its axis φ of the eye 12. The spherical equivalent SE of the eye 12 is compensated by shifting the focusing lens group 90 along an optical axis, as indicated by a double arrow 96. In this embodiment, therefore, not the entire module AOM is movable along an optical axis, but only the lens group 90 within the module AOM. In this embodiment, the relationship between the spherical equivalent SE and the position of the focusing lens group 90 along an optical axis is not linear, but can be easily determined from the focal lengths of the lens groups involved and the geometry of the optics 22 analogously to equation (2). The adaptive component 94, which can be configured as a Stokes lens, is positioned in the exemplary embodiment close to a plane conjugate to the pupil P of the eye 12. Therefore, if the adaptive component 94 is configured as a Stokes lens, the rotation of the two cylindrical lenses of the Stokes lens about an optical axis is independent of any spherical refractive error of the eye 12 and depends only on the astigmatism C and its axis position φ of the eye 12. However, it is also conceivable to position the adaptive component 94 at a different position in the measuring beam path. The procedure shown in Fig. 8 can be used to measure the refraction of eye 12. Fig. 10 shows another embodiment of a refractometer 10 for measuring the refraction of a patient's eye 12. In this embodiment, a measuring light beam is emitted from one end 52 of an optical fiber 50, the emitted measuring light having, for example, a wavelength λ of 840 nm. The optics 22 of the refractometer 10 have an adaptive optical module AOM, which includes a lens group 100 and an adaptive component 102. The adaptive component 102 serves to compensate for astigmatism and its axis position of the patient's eye 12. The lens group 100 collimates the measuring light beam exiting the end 52 of the optical fiber 50. The lens group 100 is movable along an optical axis to compensate for the spherical equivalent of the ametropia of the eye 12, as indicated by arrow 104. The adaptive component 102 can consist of two cylindrical lenses arranged at a fixed angle to each other, for example, as liquid-filled lenses, or it can be implemented as a pair of Alvarez plates that can be moved relative to each other. In the case of two crossed cylindrical lenses with variable refractive power, astigmatism of a given magnitude C of the eye 12 and an axis φ is compensated by adjusting the refractive power of the cylindrical lenses. The optics 22 further comprises two lens groups 106 and 108, which, as in the embodiment shown in Fig. 5, can together form a Keplerian telescope. The ellipses on the right edge of the image in Fig. 10 schematically show patient eyes with spherical equivalents from SE = + 10D (top) to SE = - 10D (bottom). From the adjustable position of the collimating lens group 100 as well as from the refractive powers of the variable refractive power cylindrical lenses of the adaptive component 102 and their fixed positioning, the spherical equivalent SE, the astigmatism C and the axis position φ of the astigmatism of the eye 12 can again be determined. Fig. 11 shows another embodiment of a refractometer 10 for determining or measuring the refraction of a patient's eye 12. In the refractometer 10, the entire optics 22 are formed by the adaptive optical module AOM. In other words, the AOM module comprises all the optical components of the refractometer 10. A measuring light beam is emitted from a measuring light source (for example, measuring light source 14 in Fig. 2) from one end 52 of the optical fiber 50. The optical fiber 50, and thus its end 52, is movable along an optical axis, as indicated by arrows 110. In this configuration of the refractometer 10, only the optical fiber 50 needs to be moved along the optical axis to adjust the adaptive optical module AOM so that the spherical equivalent of the ametropia of the eye 12 is compensated. In the measuring beam path of the refractometer 10, viewed from the measuring light source or the optical fiber 50, there is a folding mirror 112, a lens group 114, a folding mirror 116 (which can also be designed as a beam splitter like the beam splitter 36 with a downstream image sensor and / or display 40) and an adaptive component 118. The optical fiber 50, the folding mirror 112, the lens group 114, the folding mirror 116 and the adaptive component 118 form the AOM module.To compensate for the spherical equivalent SE, the end 52 of the optical fiber 50 is shifted along its emission direction (arrow 110). Astigmatism C and axis φ can be compensated by adjusting the adaptive component 118, which can, for example, be designed as a Stokes lens. To stabilize the signal amplitude by eliminating the effect of speckles and retinal inhomogeneities, the folding mirror 112 can vibrate, as indicated by arrows 120, so that the light spot 28 on the retina 23 also moves. Figure 11 shows the displacement paths of the optical fiber 50 and its end 52 relative to a zero position Δz0 for a spherical equivalent SE = 0D, where Δz1 is for SE = +10D and Δz3 is for SE = -10D. For example, Δz1 is -16.13 mm and Δz3 is +15.85 mm. The design of the refractometer 10 in Fig. 11 has the advantage that astigmatism and its axis directly correspond to the values ​​on the spectacle lens and no longer need to be converted. Furthermore, the measuring light beam at the pupil P of the eye 12 is significantly larger than the pupil itself. Thus, a measurement is possible even if the patient's eye 12 is decentered relative to an optical axis of the refractometer 10. In addition, the design is very compact and cost-effective to implement. In the previously described refractometers 10 and the method for measuring the refraction of a patient's eye, the settings of the adaptive optical module AOM for compensating the spherical equivalent SE, the astigmatism C, and its axis φ can be controlled via the control unit 38. The control unit 38 derives the respective control signal from the measuring module 18, which evaluates the intensity of the back-reflected measuring light measured by the light detector 20. The measuring module 18 records the intensity profile of the back-reflected measuring light measured at the light detector 20, as shown, for example, in Figures 6 and 7 using exemplary intensity curves. Further embodiments of adaptive optical modules, in particular for use in the refractometers 10 according to Fig. 1 and Fig. 4, are described below. For example, a continuously adjustable monocular phoropter based on liquid lenses can be used as the AOM module, as described in the article by R. Marks et al.: “Adjustable adaptive compact fluidic phoropter with no mechanical translation of lenses”, Optics Letters, Vol. 35, No. 8, pp. 739 ff. (2010). The values ​​set on the phoropter for spherical equivalent, astigmatism, and its axis position, at which the maximum signal is measured at the light detector 20, describe the refraction of the eye without further conversion. Another way to implement a monocular phoropter is to use a pair of Alvarez plates, as described in US 8,688,338 B2, a document referenced in this description. When the two plates, each with a complementary surface contour, are moved relative to each other in a direction x perpendicular to an optical axis z, the spherical refractive power of the Alvarez pair varies, thereby compensating for the spherical equivalent of the patient's ametropia. When the plates are moved relative to each other in a direction y perpendicular to the xz-plane, the astigmatism varies. When both Alvarez plates are rotated together around an optical axis z, the axis position varies. Such an adaptive optical module (AOM) design has the advantage of allowing simultaneous objective and subjective refraction measurements. Another variation of this embodiment is the positioning of two refractometers 10 next to each other, so that both patient eyes can be measured simultaneously. The refractometers 10 described here can be designed as stand-alone devices, for example in the form of a tabletop instrument. However, it is also possible to combine a refractometer 10 according to the invention with an OCT device for eye examination into a combined device, as shown schematically in Fig. 12. Fig. 12 shows an OCT device 160 in which a refractometer 10 according to the invention is integrated. The OCT device 160 is used for optical coherence tomography examination of an eye 12. The OCT device comprises an OCT light source, an interferometer, and a photodetector, these components being contained in a block 162 in Fig. 12. In this case, the measuring light source 14 of the refractometer 10 can be the OCT light source and / or the light detector 20 of the refractometer 10 can be the light detector of the OCT system. As in the embodiments shown in Fig. 2, Fig. 3 to Fig. 4 and 5, 9 to 11, an optical fiber 50 can be used to emit a measuring light beam and receive back-reflected measuring light for the refraction determination of the eye 12, and the same optical fiber 50 can emit OCT light and receive back-reflected OCT light for the purposes of an optical coherence tomographic examination of the eye 12.A lens group 164 can collimate both the measuring light for refraction determination and the OCT light. An adaptive optical module AOM with an adaptive component 169 designed as a Stokes lens, shown in neutral setting in Fig. 12, for compensating astigmatism, and a translationally movable lens group 171 for compensating the spherical equivalent, is used for refraction determination as described above, whereby the AOM module can also be used for OCT examination. Scanning mirrors 166, 168, which are common for OCT devices, can not only be used for OCT measurement, but can also serve to spatially vary the light spot 28 on the retina 23 and thus eliminate undesirable influences of inhomogeneities of the retina 23 and also of speckles, as already described above. Using the scan mirrors 166 and 168, the retina 23 or the anterior chamber of the eye 12 can be scanned perpendicular to an optical axis during an OCT examination. By adding the AOM module, the OCT device also gains the functionality of a refractometer. During the refraction measurement of the eye 12, the OCT signal can be evaluated to ensure that the measuring light is located in the fovea and that the patient's eye is looking in the correct direction. Furthermore, an improvement in OCT image quality is achieved because the AOM module eliminates astigmatism of the eye 12 in the wavefront of the OCT beam path, thus resulting in increased lateral resolution of the retina 23 in the OCT image. In further embodiments of the refractometer 10, the adaptive optical module can also include adaptive components that can be used to compensate for one or more higher-order aberrations of the eye 12, such as coma, trile leaf aberration, etc. Such an adaptive component can be, for example, an adaptive mirror or a liquid crystal-based spatial light modulator. Higher-order aberrations are understood here to mean all aberrations that cannot be described by the three Zernike functions for defocus and astigmatism. By compensating for these higher-order aberrations, the signal amplitude at the light detector 20 can also be influenced. The higher-order aberrations of the eye can then be derived from the setting of the adaptive component and thus the wavefront at the adaptive component. As described above, it is advantageous to arrange the adaptive component of the adaptive optical module in a plane conjugated to a surface of the eye, such as the cornea or the iris. The advantage is that the compensated aberrations are then independent of each other; for example, the compensated astigmatism does not depend on the spherical equivalent of the ametropia. Furthermore, in the refractometers according to the invention, it is advantageous to place the wavelength of the measuring light in the infrared wavelength range so that the patient is not dazzled and the patient's pupil remains dilated. This design is also particularly suitable for combining the refractometer according to the invention with an OCT device, since the OCT light source typically emits OCT light in the infrared wavelength range. Further adaptive components for use with the adaptive optical module AOM of the refractometer 10 according to the invention can, for example, be liquid lenses based on the electro-wetting effect or rotationally symmetric membrane lenses. Instead of rotating the two cylindrical lenses of a Stokes lens to determine the axis position, corresponding prisms such as a Schmidt-Pechan prism or an Abbe-König prism, which are rotatable in the beam path, can also be used. Thus, only one cylindrical lens of the Stokes lens needs to be rotatably mounted. The refractometers 10 described above according to the invention can also have two or more adaptive optical modules (AOMs), one of which, for example, serves to compensate for the spherical equivalent of ametropia and the other for astigmatism. Such multiple AOM modules can be arranged at two different locations in the measurement beam path. For example, the AOM module for astigmatism and axis compensation can be positioned in front of the patient's eye 12, and the AOM module for compensating the spherical equivalent can be positioned in the region of the end 52 of the fiber 50. Furthermore, it is understood that the adaptive optical modules described above can be designed not only as a single, coherent block of optical components, but that the optical components for compensating the spherical equivalent and for compensating astigmatism can be arranged at different locations and distances from one another in the measurement beam path. In further embodiments, a refractometer 10 according to the invention can have an optional camera that captures an image of the iris of the patient's eye and is coupled via the beam splitter 36 (Fig. 1), as already described above with reference to Fig. 1 (image sensor 40). The image from the camera can be used to start or interrupt the refraction measurement process, depending on whether the patient's eye 12 is in a suitable position relative to the measuring light beam 16. This can reduce measurement errors. If the refraction measurement is performed with infrared measuring light, the values ​​determined by the refractometer 10 for the spherical equivalent SE and astigmatism C can be converted to corresponding values ​​in the visual spectrum, for example at 550 nm.

Claims

Confocal refractometer for determining the refraction of a patient's eye (12), comprising a measuring light source (14) for generating a measuring light beam (16), a measuring module (18) having a light detector (20) for measuring the intensity of the measuring light, and further comprising optics (22) through which a measuring beam path is traversed to direct the measuring light beam (16) onto the retina (23) of the eye (12) and to direct back-reflected measuring light (24) from the retina (23) to the light detector (20), wherein the measuring beam path is confocal overall, wherein the optics (22) has an adaptive optical module (AOM), wherein by adjusting the adaptive optical module (AOM) a wavefront of the measuring beam path can be changed so that the intensity of the back-reflected measuring light (24) measured by the light detector (20) changes, wherein the measuring module (18) is designed to, by means of an adjustment of the adaptive optical module (AOM),to determine the spherical equivalent (SE) of the ametropia of the eye (12) when the measured intensity of the back-reflected measuring light (24) has a maximum, characterized in that the adaptive optical module (AOM) has an adaptive component (74; 94; 102; 118) which is designed to compensate for astigmatism in the wavefront of the measuring light by adjusting the adaptive component (74; 94; 102; 118), and wherein the measuring module (18) is designed to determine the astigmatism (C) of the eye and the axis (φ) of the astigmatism from a setting of the adaptive component (74; 94; 102; 118) when the measured intensity of the back-reflected measuring light (24) has a maximum. Refractometer according to claim 1, characterized in that the adaptive component (74; 94; 102; 118) can be adjusted to a neutral setting in which the adaptive component (74; 94; 102; 118) has no astigmatic effect. Refractometer according to claim 1 or 2, characterized in that the adaptive component (74; 94; 118) has two cylindrical lenses rotatable relative to each other, one of which has a positive refractive power and the other of which has a negative refractive power, wherein the positive and the negative refractive power are of equal magnitude. Refractometer according to claim 1 or 2, characterized in that the adaptive component has two plates, each having a surface contour, wherein the two surface contours are complementary to each other, and wherein the plates are translationally displaceable and / or rotatable relative to each other. Refractometer according to claim 1 or 2, characterized in that the adaptive component (102) has one or more liquid-filled lenses whose spherical and / or astigmatic refractive power is variable. Refractometer according to claim 5, characterized in that the adaptive component (102) has two cylindrical lenses which are crossed relative to each other at an angle other than 0°, wherein the cylindrical lenses are in particular fixed in position relative to each other, and wherein the refractive power of the cylindrical lenses is variable. Refractometer according to one of claims 1 to 6, characterized in that the adaptive component (74) is positioned in the measuring beam path in a plane which is conjugated to the pupil (P) of the eye (12) in the use of the refractometer (10). Refractometer according to one of claims 1 to 7, characterized in that a first aperture (27) is arranged near the measuring light source (14) and a second aperture (31) is arranged near the light detector (20), wherein the first and the second aperture (27, 31) are confocal. Refractometer according to one of claims 1 to 7, characterized in that the measuring light source (14) is connected to a first optical fiber (44) and the light detector (20) is connected to a second optical fiber (46), wherein the first and the second optical fiber (44, 46) transition via a fiber coupler (48) into a third optical fiber (50), wherein a free end (52) of the third optical fiber (50) forms an exit end for the measuring light beam (16) and an entry end for the back-reflected measuring light (24), wherein the exit end and the entry end are confocal. Refractometer according to claim 9, characterized in that a lock-in amplifier (54), in particular a chopper wheel (56), is arranged in the measuring beam path. Refractometer according to one of claims 1 to 10, characterized in that a deflection element (60) is arranged in the measuring beam path, which periodically deflects the measuring light beam (16) such that the measuring light beam (16) is periodically moved on the retina (23) of the eye (12) during use of the refractometer. Refractometer according to one of claims 1 to 11, characterized in that the optics (22) has a beam splitter (36) to which a display and / or an image sensor (40) is associated. Refractometer according to one of claims 1 to 12, characterized in that the adaptive optical module (AOM) comprises an optical fiber (50), a first lens group (72), the adaptive component (74) and a second lens group (76), wherein the adaptive component (74) is arranged near the focal plane of the second lens group (76). Refractometer according to claim 13, characterized in that the optics (22) has a third lens group (78), wherein the third lens group (78) is arranged such that, in use of the refractometer (10), the pupil (P) of the eye (12) is located near a focal plane of the third lens group (78). Refractometer according to claim 14, characterized in that the optical fiber (50), the first lens group (72), the adaptive component (74) and the second lens group (76) are jointly movable in the direction of the measuring beam path relative to the third lens group (78). Refractometer according to one of claims 1 to 12, characterized in that the adaptive optical module (AOM) comprises a first lens group (90), a second lens group (92) and the adaptive component (94), wherein the first lens group (90) is movable along the measuring beam path relative to the second lens group (92). Refractometer according to claim 16, characterized in that the optics (22) comprises an optical fiber (50), a third lens group (88) and the adaptive optical module (AOM), wherein the optical fiber (50) and the first lens group (88) are preferably stationary. Refractometer according to one of claims 1 to 12, characterized in that the adaptive optical module (AOM) has a first lens group (100) and the adaptive component (102), wherein the first lens group (100) is movable in the direction of the measuring beam path relative to the adaptive component (102). Refractometer according to one of claims 1 to 12, characterized in that the adaptive optical module (AOM) comprises an optical fiber (50), a first folding mirror (112), a lens group (114), a second folding mirror (116) and the adaptive component (118). Refractometer according to claim 19, characterized in that at least one of the folding mirrors (112, 116) is movable to move the measuring light beam (16) on the retina (23) during use of the refractometer. Refractometer according to claim 19 or 20, characterized in that the optical fiber (50) is movable in the direction of the measuring beam path relative to the first folding mirror (112). Refractometer according to one of claims 19 to 21, characterized in that the optics (22) comprise only the adaptive optical module (AOM). Refractometer according to one of claims 1 to 22, characterized in that the adaptive optical module (AOM) is designed to compensate for aberrations of a higher order than the fundamental order of astigmatism in the wavefront. Refractometer according to claim 23, characterized in that the higher order aberrations are those that cannot be described by the three Zernike functions for defocus and astigmatism. Refractometer according to one of claims 1 to 24, characterized by a control unit (38) for adjusting the adaptive optical module (AOM). Refractometer according to claim 25, characterized in that the control unit (38), in particular in conjunction with the measuring module (18), is configured to adjust the adaptive optical module (AOM) so that the intensity of the back-reflected measuring light (24) measured at the light detector (20) has a maximum. Refractometer according to claim 25 or 26, characterized in that the control unit (38) is configured to adjust the adaptive optical module (AOM) first during a neutral setting of the adaptive component (74; 94; 102; 118), in which the adaptive component (74; 94; 102; 118) has no astigmatic effect, until the intensity measured at the light detector has a maximum. Refractometer according to claim 27, characterized in that the measuring module (18) is configured to determine, at least approximately, the spherical equivalent (SE) and the astigmatism (C) from the respective setting of the adaptive optical module (AOM) when a first and second maximum is detected at the light detector (20). Refractometer according to claim 27 or 28, characterized in that the measuring module (18) is configured to determine the spherical equivalent (SE) from the setting of the adaptive optical module (AOM) when only a maximum of the intensity is detected at the light detector (20) and to determine the astigmatism (C) as at least approximately zero. Refractometer according to one of claims 26 to 29, characterized in that the control unit (38) is configured to adjust the adaptive component (74; 94; 102; 118) from the neutral setting so that the adaptive component (74; 94; 102; 118) compensates for the astigmatism regardless of its axis position, and to further adjust the adaptive component (74; 94; 102; 118) until the intensity detected at the light detector (20) no longer increases, wherein the measuring module (18) is configured to determine the axis position (φ) of the astigmatism from the resulting setting of the adaptive component (74; 94; 102; 118). OCT device for optical coherence tomography examination of a patient's eye, characterized by an integrated refractometer (10) according to one of claims 1 to 30, wherein the measuring light source (14) is formed by an OCT light source. Method for determining the refraction of an eye (12) of a patient, comprising the steps of: providing a measuring beam path in which an adaptive optical module (AOM) is arranged, which is designed to compensate for a spherical equivalent (SE) of the ametropia of the eye in the wavefront of the measuring beam path by adjusting, and which has an adaptive component (74; 94; 102; 118) designed to compensate for astigmatism in the wavefront of the measuring beam path by adjusting; directing a measuring light beam (16) onto the eye (12) such that a spot of light (28) is produced on the retina (23) of the eye (12); measuring an intensity of measuring light (24) reflected from the retina; adjusting the adaptive optical module (AOM) and the adaptive component (74; 94; 102; 118) until the The measured intensity is at its maximum, determined from the setting of the adaptive optical module (AOM) and the adaptive component (74; 94; 102;118), at which the measured intensity is maximal, the spherical equivalent (SE), the astigmatism (C) and its axis position ( <p).;

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