Method and device for measuring wavefront of human eye

Abstract

A method and apparatus for measuring a wavefront of a human eye relative to an objectively determined optical axis is provided, wherein the optical axis is determined prior to measuring the wavefront. The optical axis is defined in a direction directed towards the fovea, indicated by a bisector of two orthogonal laser beams that hit the fovea at points of slope equal depth of the fovea. The wavefront is measured by detecting the eye with a laser beam oriented along an optical axis at a set of points in the pupil. Backscattered radiation is detected, the coordinates of the laser spot on the retina are measured, and the wavefront is reconstructed from the refractive distribution on the pupil.

Description

[0001] Cross - reference to related applications

[0002] This international patent application claims priority under 35 U.S.C.§119(e) to U.S. Provisional Application No. 63 / 403,686, filed on September 2, 2022, the entire content of which is incorporated herein by reference. Technical field

[0003] The present invention generally relates to the field of ophthalmic instruments for examining the eye. More specifically, the present invention relates to ophthalmic examination instruments for measuring and characterizing the refractive properties of the eye with high precision using objectively determined positioning. Background art

[0004] If the human eye were a perfect optical system, its optical axis would be defined by the points spanning the centers of the two optical components, the cornea and the lens. Since the eye is not a perfect optical system, the term "optical axis of the eye" can only mean a rough approximation and is not suitable for accurately describing features that are very important for diagnosis and surgery. The pupil axis and the line of sight are other approximations.

[0005] When videokeratography was the only diagnostic means, the centering process was focused on the corneal apex using the pupil axis determined by the center of the Purkinje reflection. With the advent of wavefront sensing for measuring eye aberrations involving the line of sight, when the angular value between the line of sight and the pupil axis is greater than 2° - 3°, if this misalignment is ignored, it can lead to incorrect estimation of corneal and internal aberrations, as well as incorrect estimation of the corneal / internal aberration balance, and ultimately may result in correction errors.

[0006] The recommendations in ANSI standard Z80.28 - 2004 and the later international standard ISO / FDIS 24157:2008(E) stipulate that wavefront measurements should be referenced to the pupil center with the line of sight as the reference axis. The attractive argument is the ease of specifying the center of the pupil entrance, but the visual axis does not provide a constructive reference for anchoring the measuring instrument to the eye.

[0007] The definition of the visual axis includes two straight - line segments: "fixation point - first nodal point" and "second nodal point - center of the foveola". Since the distance between the nodal points is very small, this definition is usually simplified to "fixation point - nodal point - center of the foveola". Since the internal part of the visual axis is actually an extension of its external part, this definition can be further simplified: "fixation point - center of the foveola". There is no evidence that in the axially asymmetric optical system of the eye, the intersection of the straight line "fixation point - center of the foveola" with the pupil is at the Purkinje reflection center or the geometric center of the pupil, as its shape affects the position of the center.

[0008] Using different reference axes in corneal topography, optical coherence tomography, aberration measurement, and refractive measurement makes it difficult to integrate data from different instruments. The main reason for this is that many current laser companies and surgeons mistakenly believe that ablation is centered on the pupil entrance center rather than the visual axis. Reinstein et al. attempted to define the visual axis as the axis with the least aberration measured through a virtual pupil in U.S. Patent No. 8,444,632, where the center of the virtual pupil is anchored to the coordinates of the actual pupil. Wakil et al. extended this attempt in U.S. Patent No. 9,271,647 by changing the mathematical search program for the virtual pupil to iterative ray tracing to locate the axis with the least aberration and using it as the best visual axis. Both of these solutions actually replace the visual axis with an approximation (still called the "visual axis"), which, according to the suggestion, should have the same least aberration as the actual visual axis and should result in better surgical outcomes compared to the line-of-sight-centered scheme.

[0009] In Ukrainian Patent No. 114043, Molebny proposed determining the position of the visual axis according to the definition in textbooks, where the fovea centralis is specified by its deepest point. The direction at this point is found by reconstructing the topographic map of the fovea centralis pit, as described in the publication (V. Molebny. "Method for objective localization of the visual axis", Ophthalmic and Physiological Optics, 2017; 37, 326 - 332, doi: 10.1111 / opo).

[0010] Determining the corneal intersection point through the visual axis allows one to consider the corresponding changes in eye parameters and use this data to measure other characteristics of the eyeball, or perform vision correction through corneal tissue ablation, or determine the position of an implant, or replace the lens with an intraocular lens in the correct orientation.

[0011] The Molebny method described in Ukrainian Patent No. 114043 requires a certain amount of time to reconstruct the retinal topographic map of the fovea centralis region point by point. It is recognized that there is a need to speed up this process.

[0012] The deficiencies of the prior art lie in the lack of instruments and methods capable of measuring and characterizing the refractive properties of the eye with high precision. The present invention meets the long - standing needs and desires in this field. Summary of the Invention

[0013] The present invention provides a method and apparatus for wavefront measurement of the human eye relative to an objectively determined visual axis. The method of the present invention uses ray tracing to measure the refractive parameters of the eye, where the optical axis of the device is oriented along the visual axis of the eye, and the visual axis is defined as the straight line connecting the fixation point and the center of the fovea centralis. The center of the fovea centralis is determined as the deepest point in the fovea centralis pit, and its direction is indicated by the bisector of two laser beams symmetrically adjacent to the opposite pit slopes.

[0014] The process of wavefront measurement is provided by measuring the refractive parameters of the eye by ray tracing with a laser beam, which is deflected by a biaxial acousto-optic deflector after passing through a telescope and a collimating lens and then enters the eye. The light backscattered from the retina is detected by a position sensing detector. The refractive parameters of the eye are calculated by a processing unit.

[0015] At the start of the measurement, the direction of the visual axis is first determined. By a command from the processing unit, the laser beam is continuously split ("doubled") in the X and Y directions, thus providing the possibility of defining the direction towards the center of the fovea by their bisectors. The splitting of the beam is achieved by the same acousto-optic deflector, each having two different frequencies, the difference between which corresponds to a beam splitting angle on the order of 10 mrad.

[0016] The search for the position of the bisector specifying the visual axis direction is provided by measuring the phase difference between the split beam pairs in the X and Y directions, respectively. This phase difference is measured according to the difference frequency applied to the acousto-optic deflector. The reference signal for phase discrimination comes from the generator driving the deflector. The phase of the reference signal is compared with the phase of the low-frequency component filtered at the output of the coherent detector, which receives the signal corresponding to the split beam after backscattering from the retina. The search for the bisector position is controlled by the processing unit.

[0017] This search starts after conjugating the retina with the detector plane using an electro-controlled conjugate telescope mounted in front of the eye. The measurement of the refractive parameters is carried out with the optical axis of the device aligned along the direction of the visual axis of the eye. From the following description of the currently preferred embodiment of the present invention given for the purpose of disclosure, the details of the schematic diagram and the functional details, other and further aspects, features and advantages of the present invention will become apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] For a detailed understanding of the features of the present invention described above, the present invention outlined briefly above is illustrated in more specific detail in the accompanying drawings. These drawings form a part of the specification. However, although the drawings illustrate the preferred embodiments of the present invention, they should not be considered as limiting the scope of the present invention.

[0019] Figure 1 Shows the definitions of the visual axis of the eye, the pupil axis, the symmetry axis (also called the optical axis), the line of sight, the angle k (kappa) between the visual axis and the pupil axis, and the angle λ (lambda) between the line of sight and the pupil axis.

[0020] Figure 2 Shows the designation of the pupil center as the geometric center of a set of first Purkinje reflections from the outer surface of the cornea with a cross-shaped marker.

[0021] Figure 3 It is a schematic diagram of the center of the pit where the visual axis of the eye passes through the foveola centralis area.

[0022] Figure 4 It is a functional schematic diagram of a device, showing that wavefront measurement is related to the visual axis determined by the device.

[0023] Figures 5A - 5E It shows the steps of forming a detection laser beam. Figure 5A It shows two beam diffraction orders in the X and Y directions, where the first digit represents the diffraction order in the X direction and the second digit represents the diffraction order in the Y direction, and the detection uses the first diffraction order in both the X and Y directions. Figure 5B It shows the spatial filtering for selecting the first diffraction order beam. Figure 5C It shows the positioning of a single beam in the wavefront measurement mode. Figure 5D It shows the beam splitting (double beam formation) in the X direction in the visual axis specifying mode. Figure 5E It shows the situation in the Y direction Figure 5D the same as

[0024] Figure 6 It shows the path of the double beam (X direction beam splitting) from the laser 1 to the collimating lens 15 (without scaling). In the Figure 4 schematic diagram, the lens is replaced by the principal plane of its thin equivalent. The definition of the bisector applies from the splitting point along the entire path until the retina.

[0025] Figures 7A - 7C It shows the path of the double beam reaching the eye after passing through the collimating lens. Figure 7A It shows an emmetropic eye, where the fluid lens is in the initial position corresponding to the afocal requirement of the telescope 18 - 20. Figure 7B It shows a myopic eye, and the focus of the lens 18 is shifted to a longer value. Figure 7C It shows a hyperopic eye, and the focus of the lens 18 is shifted to a shorter value. In both cases ( Figure 7B and Figure 7C ), the refractive anomaly of the eye will be compensated.

[0026] Figure 8 It shows the positional relationship of the C VA , Y VA points on the cornea where the visual axis passes through when it is offset in the VA direction relative to the C LOS points. The CLOS point is defined as the center of the Purkinje image, that is, the intersection of the presumed visual line path and the cornea.

[0027] Figure 9Shows the path of the two beams (split in the X direction) in the target area (fovea). The depth of penetration of the light into the retinal tissue depends on the wavelength; however, for the beams offset by Fx1 and Fx2, the difference in penetration does not play any role.

[0028] Figures 10A - 10C Shows Figure 4 The phase difference measured by the phase discriminator 29 of the schematic diagram How it is used as an error signal to position the bisecting line to coincide with the visual axis of the eye. In Figure 10A When The signal error Δx is also >0; in Figure 10B When The signal error Δx is also <0; in Figure 10C When The bisecting line coincides with the visual axis. There is a similar dependence in the Y direction. Detailed implementation

[0029] As used herein, the articles "a" and "an" when used in the claims and / or the specification in conjunction with the term "comprising" can mean "one", but also conform to the meanings of "one or more", "at least one", and "one or more than one". Some embodiments of the present invention may consist of or consist essentially of one or more elements, components, method steps, and / or methods of the present invention.

[0030] As used herein, the term "or" in the claims refers to "and / or", unless explicitly stated to refer only to alternative options or the alternative options are mutually exclusive, and the content of the present disclosure supports the definition of only alternative options and "and / or".

[0031] The terms "comprise" and "comprising" used herein are inclusive and open-ended, meaning that other elements may be included.

[0032] The terms "consists of" and "consisting of" used herein are exclusive and closed-ended, meaning that other elements may not be included.

[0033] The terms "includes" or "including" used herein mean "including but not limited to". The terms "includes", "including", and "including but not limited to" can be used interchangeably.

[0034] As used herein, the term "about" refers to a numerical value, including, for example, integers, fractions, and percentages, whether or not explicitly stated. The term "about" generally refers to a range of numerical values (e.g., ±5-10% of the corresponding numerical value) that a person of ordinary skill in the art would consider equivalent to the corresponding numerical value (e.g., having the same function or result). In some cases, the term "about" may include a numerical value rounded to the nearest significant digit.

[0035] In one embodiment of the present invention, a method for measuring the wavefront of a human eye relative to an objectively determined visual axis is provided, comprising continuously probing a set of points within the pupil of the eye with a laser beam over time; detecting the radiation backscattered from the retina of the eye; measuring the coordinates of the laser spots on the retina; and reconstructing the wavefront based on the refractive distribution on the eye pupil; wherein the laser beam for probing the eye is oriented along the visual axis of the eye during wavefront measurement, and wherein the visual axis is determined prior to wavefront measurement by the following steps: splitting the laser beam into double beams separately in the X and Y directions; probing the foveal pit region of the retina with the double beams in both the X and Y directions of beam splitting; detecting the laser light backscattered from the foveal pit region; measuring and comparing the phase shifts of the beams in the double beams relative to each other in both the X and Y directions of beam splitting; determining the direction of the double beams at the position of equal depth of the relative slopes of the foveal pit indicated by the zero value of the phase shift between the beams in the double beams; and designating the visual axis as the bisector of the double beams, the bisector being located at the position of equal depth of the relative slopes of the central pit in both the X and Y directions of beam splitting.

[0036] In this embodiment, beam splitting may include diffraction in a biaxial acousto-optic deflector separately in the orthogonal directions in the pupil plane. Additionally in this embodiment, beam splitting may also include diffraction in a biaxial acousto-optic deflector separately in the orthogonal directions on the pupil plane. Further, there may be a depth difference on the relative slopes of the foveal pit, which is defined as the phase difference between the carrier frequencies of the separated beams, and this phase difference is converted into the phase difference between the signals of the frequency differences between the carrier frequencies of the aforementioned double beams. Additionally, the probing directions of the double beams may be changed until the phase difference values in both orthogonal directions become zero.

[0037] In another embodiment of the present invention, there is provided an apparatus for wavefront measurement of the human eye relative to its objectively determined visual axis, comprising a laser configured to emit a laser beam having a wavelength suitable for ray tracing; a pair of diffraction-based deflectors composed of acousto-optical crystals, including a first deflector oriented to deflect the laser beam in a first direction orthogonal to the propagation direction of the laser beam and a second deflector oriented to deflect the laser beam in a second direction perpendicular to the first direction, each of the first deflector and the second deflector in this pair of deflectors having an entrance aperture and an exit aperture, and each of the first deflector and the second deflector in this pair of deflectors being positioned along the path of the laser beam such that their effective deflection centers are substantially coincident; a pair of drivers including a first driver operatively connected to a first frequency generator and a second driver operatively connected to a second frequency generator, each of the first driver and the second driver in this pair of drivers being configured to acousto-optically drive the first deflector and the second deflector respectively; a telescope and a collimating lens (CL) placed in optical alignment with the deflection centers of the first deflector and the second deflector in this pair of deflectors in sequence; a first beam splitter placed on the path of the laser beam reaching the human eye and the reflected radiation from the human eye; a position sensing detector placed on the path of the reflected radiation from the human eye; and a processing unit operatively communicating at least with the laser, the first frequency generator, the second frequency generator, and the position sensing detector; wherein a third frequency generator is connected to the first driver; a first frequency difference filter is connected to the first driver such that the first frequency difference is the difference between the frequencies generated by the first frequency generator and the third frequency generator; a fourth frequency generator is connected to the second driver; a second frequency difference filter is connected to the second driver such that the second frequency difference is the difference between the frequencies generated by the second frequency generator and the fourth frequency generator; the first frequency difference and the second frequency difference are established to be equal to each other, and a coherent detector is configured at its output with the first frequency difference and the second frequency difference; an electrically controlled conjugating telescope is placed at an adjustable refractive index position between the above-mentioned first beam splitter and the human eye to optically conjugate the plane of the retina with the plane of the position sensing detector and the plane of the coherent detector; a coherent detector is installed on the laser radiation path after the first beam splitter, there is an aperture in front of the coherent detector, and the output end of the coherent detector has a low-pass filtering function;A phase discriminator (PD) is provided at the output of the above-mentioned coherent detector. The phase discriminator has two switchable input terminals, namely a first reference input terminal connected to the output terminal of the first frequency difference filter and a second reference input terminal connected to the output terminal of the second frequency difference filter; and a third frequency generator, a fourth frequency generator, an electro-optic conjugate telescope, and a phase discriminator that are operably communicable with the processing unit.

[0038] In this embodiment, the first beam splitter may be a polarizing beam splitter and is configured to allow linearly polarized light from the laser to pass through the polarizing beam splitter and be transmitted to the human eye, and reflect the orthogonal part of the depolarized radiation from the human eye and guide it to the position-sensitive detector and the coherent detector. In addition, in this embodiment, the position-sensitive detector has a dual-channel configuration corresponding to the first orthogonal direction and the second orthogonal direction of the position measurement.

[0039] As described above, the optical parameters of the eye can be most fully described with reference to the visual axis, which is defined as the line connecting the fixation point at infinity and the center of the fovea centralis ( Figure 1 ). The intermediate point where the visual axes cross is the first node and the second node, which are usually regarded as a single point (N), simply referred to as the node, due to the small distance between them (about one-quarter millimeter). The visual axis has another name - the nodal axis. Since the node can only be determined in a virtual manner and cannot be anchored to any visually perceivable mark or structure, the visual axis is usually replaced by the line of sight (LOS). The line of sight is defined as the line connecting the far vision center point (fixation point, target) and the pupil center. Most wavefront instruments recommend that the pupil center coincide with the corneal apex, which is designated as the center of a set of first Purkinje images (reflections of four or six point light sources, usually from light-emitting diodes LEDs).

[0040] For example, Figure 2 illustrates an eye pupil with a cross mark at the center C LOS The cross mark is the Purkinje reflexes P a , P b , P c , P d of the light from four infrared light-emitting diodes. This point is considered to be the point where the line of sight passes through the cornea.

[0041] The visual axis passing through the center F of the fovea centralis is as Figure 3As shown. The size of the pit is approximately 0.35 millimeters. The task of the first measurement is to find the direction of point F at the position where the eye is looking at an infinitely distant target point.

[0042] Refer to Figure 4 The functional schematic diagram of the device describes the method and steps of the solution. In this device, the output end of the laser 1 is connected to the input end of the first deflector 2, and the scanning center of the first deflector 2 is located at O x point. The second deflector 3 is installed in series with the first deflector 2. The scanning center of the second deflector 3 is O y . The first deflector 2 and the second deflector 3 can be of any type, but considering the deflection and scanning speed, an acousto-optic deflector based on the principle of light diffraction on a grating can be recommended, and its grating is generated by ultrasonic waves in an acousto-optic crystal.

[0043] For the purpose of the present invention, the scanning centers in the orthogonal directions (X and Y) should coincide. This can be provided by a telescope that converts the O x scanning center into the O y scanning center. In fact, this requirement can be ignored, and the first deflector 2 and the second deflector 3 can be designed so that their crystals are as close to each other as possible in the millimeter range. To form a diffraction grating in the crystal, drivers are required. The first driver 4 connected to the first deflector 2 is used to deflect the laser beam in the X direction, and the second driver 5 connected to the second deflector 3 is used to deflect the laser beam in the Y direction.

[0044] The deflection angle depends on the grating pitch, and the grating pitch is defined by the frequency of the high-frequency signal applied to the transducer that excites elastic waves in the crystal. Figure 5A Shows the zero-order, first-order, and second-order diffractions. The zero-order diffraction in the X direction passes through nodes 00, 01, 02, the first-order diffraction in the X direction passes through nodes 10, 11, 12. The second-order diffraction in the X direction passes through nodes 20, 21, 22. Similarly, the zero-order in the Y direction is 00, 10, 20. The first-order in the Y direction is 01, 11, 21. The second-order in the Y direction is 02, 12, 22. In our device, only the first-order diffractions in the X and Y directions passing through node 11 are used by the laser beam for angular orientation in these X and Y directions.

[0045] Selection is carried out by suppressing all orders except the first order in any way, for example, an aperture (aperture diameter) on an opaque material, as Figure 5B shown. This process is also called spatial filtering, and the mentioned aperture is called a spatial filter. The selected first-order beam can be scanned within the selection aperture to generate a sequence of directions for probing the eye during the laser ray tracing process for wavefront reconstruction or refractive distribution ([[]] Figure 5C)。For the purposes of the present invention, a single laser beam can be split in the X direction ( Figure 5D ) or in the Y direction ( Figure 5E ), thereby forming an X-split double beam or a Y-split double beam. The implementation of these configurations will be described in more detail below.

[0046] Both the first driver 4 and the second driver 5 have two input terminals ( Figure 4 ). The first input terminal of the first driver 4 is connected to the output terminal of the first generator 6 that generates the frequency F x1 . The first input terminal of the second driver 5 is connected to the output terminal of the second generator 8 that generates the frequency F y1 . The second input terminal of the first driver 4 is connected to the output terminal of the third generator 7 that generates the frequency F x2 . The second input terminal of the second driver 5 is connected to the output terminal of the fourth generator 9 that generates the frequency F y2 .

[0047] The first driver 4 and the second driver 5 can operate in two modes: the laser ray tracing mode and the line of sight designation mode. In the laser ray tracing mode, only the first input terminal of the first driver 4 is connected to the output terminal of the first generator 6. Similarly, only the first input terminal of the second driver is connected to the output terminal of the second generator 8. In the line of sight designation mode, the two input terminals of the first driver 4 are connected to the output terminals of the first generator 6 and the third generator 7, and the two input terminals of the second driver 5 are also connected to the output terminals of the second generator 8 and the fourth generator 9. The first driver 4 outputs two frequencies F x1 and F x2 to the first deflector 2 in a linear mode without frequency conversion. Similarly, the second driver 5 also emits two frequencies F y1 and F y2 to the second deflector 3 in a linear mode. The laser 1 and the first generator 6, the third generator 7, the second generator 8, and the fourth generator 9 are connected to the processing unit 10 for exchanging information and control signals.

[0048] In other words, in the laser ray tracing mode, the device uses single-beam scanning ( Figure 5C ). In the line of sight designation mode, the device uses double-beam scanning ( Figures 5D - 5E ), where the expression "double beam" refers to the beam derived from a single beam by means of splitting through an acousto-optic crystal diffraction grating. The beam splitting also results in different carrier frequencies between the split beams.

[0049] The output of the second deflector 3 is introduced into a telescope formed by two lenses 11 (L1) and 12 (L2). The path of the laser beam entering the eye is indicated by the filled arrows with texture. To make the design more compact, the optical path between the lenses 11 and 12 is bent by a mirror 13 (M1). The scanning centers O x and O y are transferred to the space behind the lens 12. Assuming that O x and O y can coincide, or the distance between them is very small and negligible, then the scanning center behind the lens 12 can be designated as O, which coincides with the rear focal point f 12 of the lens 12. In the space of the diffracted beam, the position of the scanning center O must coincide with the direction of the first-order diffraction, whether in the X direction or the Y direction. The spatial filtering of the first-order diffraction is provided by an aperture 14 (A1), and the size of the aperture should be smaller than the distance between the diffraction orders. In fact, the diameter of the aperture is about one millimeter. The center of the aperture coincides with the point O.

[0050] The next optical element on the laser beam path is a collimating lens 15 (CL). Its front focal point f' 15 coincides with the rear focal point f 12 of the lens 12, and thus coincides with the conjugate scanning center O of the center of the aperture 14 (A1). This design provides a direction parallel to the optical axis of the device for any beam after the collimating lens 15.

[0051] The path change of the laser beam from the laser 1 to the exit of the collimating lens 15 on the plane XOZ is as Figure 6 shown. The same change also occurs when the laser beam is split along the Y direction (i.e., the plane YOZ). Figure 6 The lenses in [] are replaced by the principal planes of their thin equivalents. The bisector of the split beam emitted from the equivalent point of the scan O x extends along its path to the final point on the retina. This is also valid from the perspective of the scan O y .

[0052] For the sake of clarity, the scale is not considered in the schematic diagram. It is recommended that one of the beams be split by a signal with a frequency of F x1 , and the other beam be split by a signal with a frequency of F x2 (similarly, F y1 and F y2 in the YOZ plane). The aperture 14 (A1) acts as a spatial filter - a first-order diffraction selector ( Figure 5AThe order 11) is located at the coincident foci of lenses 12 and 15, thus forming a parallel light beam at the exit of lens 15. It should be noted that a similar evolution / transformation also occurs when the light beam is scaled for wavefront measurement.

[0053] Returning to Figure 4 , it can be seen that the mirror 16 (M2) bends the direction of the light beam towards the beam splitter 17 (BS1), and then a switchable fluid lens 18, a beam splitter 19 (BS2), and a lens 20 are sequentially installed on the path to the eye 21.

[0054] The beam splitter 17 can be of any type, but for the purposes of the present invention, the best or representative example is a polarization beam splitter. It allows the vertical linear polarization of the laser beam from the last stage deflector to continue its path in the direction of the eye. The laser 1 has the same vertical linear polarization. Rotating the linear polarization by 90 degrees is a characteristic of the acousto-optic deflector unit. This means that two consecutive units will return to the original polarization type.

[0055] The path of the laser beam passing through the collimating lens 15 (CL) to the eye 21 is shown in Figure 7. Three path characteristics are shown: Figure 7A - For emmetropia (the fluid lens is in the initial position, corresponding to the afocal requirement of the telescope composed of lens 18 and lens 20 (afocal condition: the back focal length of lens 18 and the front focal length of lens 20 must coincide)); Figure 7B - For myopia (the focus of lens 18 moves to a longer value); Figure 7C - For hyperopia (the focus of lens 18 moves to a shorter value); In both cases ( Figures 7B - 7C ), the refractive anomaly of the eye will be compensated.

[0056] To achieve vergence conjugate in refractive anomaly compensation, the optical power (one of the optical powers of the fluid lens 18 is variable), the distance between lens 18 and lens 20, and the distance from lens 20 to the eye 21 will be optimized by the mathematical method described in "Defocus compensation with fluidic optics in a raytracing wavefront sensor" published by V. Molebny et al. This conjugation should be carried out both in wavefront measurement and when specifying the visual axis. This paper is included in "Proc. 7 European / 1 World Meeting on Visual and Physiological Optics", Wroclaw, 2014, pp. 222 - 225.

[0057] Return path from the eye 21 to the TV (imaging) matrix 22 ( Figure 4 ) passes through the lens 20, the beam splitter 19, and the objective lens 23 (L3). The sensitive surface of the TV matrix 22 is conjugated with the pupil of the eye through the lens 20 and the lens 23, and the lens 20 and the lens 23 form the objective lens of the matrix.

[0058] The target 24 is used to perform preliminary calibration on the patient's eye 21 and its positioning. The path of its image to the eye (solid arrow) passes through the beam splitter 25 (BS3), the beam splitter 26 (BS4), the lens 39, the beam splitter 17 (BS1), the fluid lens 18, the beam splitter 19 (BS2), and the lens 20.

[0059] In order to determine the direction at the deepest point of the fovea centralis, the coherent detector 27 is installed on the path of the light (hollow arrow) from the eye 21 passing through the lens 20, the beam splitter 19, the fluid lens 18, the beam splitter 17, the lens 39, the beam splitters 26 and 25, and the aperture 28 (A2). The output end of the coherent detector 27 includes a low-pass filter and is connected to the signal input end of the phase discriminator 29 (PD). The function of the beam splitter 17 is to reflect orthogonally polarized light to the detection area.

[0060] The phase discriminator 29 also has two other input ends: the first reference input end and the second reference input end. The first reference input end is connected to the output end of the first frequency difference unit 30, and the second reference input end is connected to the output end of the second frequency difference unit 31. The input end of the first frequency difference unit 30 is connected to the first driver 4, and the input end of the second frequency difference unit 31 is connected to the second driver 5. The output end of the phase discriminator 29 is connected to the processing unit 10. The feature of the phase discriminator 29 is that when measuring the height difference of the pit slope along the X direction, it can measure the phase shift of the signal from the coherent detector 27 relative to the reference signal ΔF x ; when measuring the height difference of the pit slope along the Y direction, it can measure the phase shift of the signal from the coherent detector 27 relative to the reference signal ΔF y . The switching between these two data is controlled by the processing unit 10.

[0061] The reference signals sent to the phase discriminator 29 are F x1 and F x2 whose frequency difference is equal to ΔF x (when defining the position along the X coordinate), or F y1 and F y2 whose frequency difference is equal to ΔF y (when defining the position along the Y coordinate) signals. The frequency difference ΔF x is obtained by the frequency difference unit 30, and the frequency difference ΔF y is obtained by the frequency difference unit 31. Generally speaking, ΔF xMay be different from ΔF y , but for simplicity in the processing, it is recommended that the two be equal: ΔF x = ΔF y = ΔF.

[0062] To measure the coordinates of the laser spot image on the retina, a position-sensitive detector composed of detectors is used. Several versions of such units are well known. One option is to measure the X and Y coordinates through separate X and Y sensors based on linear array detectors (LADs) 32 and 33, any of which has an array of photosensitive diodes oriented along the X-axis to measure the X coordinate and is oriented along the Y-axis when measuring the Y coordinate. If the laser spot is defocused, the image of the laser spot is stretched in a direction orthogonal to the direction of the diode rows by cylindrical lenses 34 and 35. The outputs of the linear array detectors 32 and 33 are connected to the processing unit 10. The path of the light scattered into the eye 21 and emerging from it is indicated by hollow arrows. The light passes through the lens 20, beam splitter 19, fluid lens 18, beam splitter 17, lens 39, beam splitter 26, beam splitter 36, and cylindrical lens 35 to reach the linear array detector 33. Before the beam splitter 36, the path to the linear array detector 32 is the same, but after the beam splitter 36, the path turns to the cylindrical lens 34.

[0063] In front of the eyeball, a set of light-emitting diodes (LEDs) 38a, 38b, etc. are installed to provide the Purkinje reflection ( Figure 2 ) from the reflecting surface of the eyeball, where the reflection from the first surface of the cornea is the most important for the function of the proposed device.

[0064] The implementation of the proposed method and device includes the following operations. First, the patient's eye fixates on a distant target. The optical axis of the instrument should be directed towards the apex of the pupil, whose position in the eye image is the center C a of the cross mark of a set of Purkinje reflections P b , P c , P d , P LOS ( Figure 2 ). The next step should be to specify the direction to the center of the fovea centralis and define the coordinates (x los , y va ) that are misaligned relative to the point C va (0, 0) in the pupil plane to represent the point C VA (X VA , Y VA ) where the visual axis passes through the cornea ( Figure 8). These coordinates may be calculated in any other coordinate system that anchors the point to the visually perceptible feature of the pupil. All the remainder of the ray tracing procedure will be performed with the instrument optical axis oriented along the specified visual axis, i.e. passing through the misaligned defined point C on the cornea. VA (X VA , Y VA ) place.

[0065] The operation of using this device is divided into two steps: the first step - specifying the boresight, the second step - measuring the wavefront.

[0066] Step 1, specify the viewing axis:

[0067] The eye image generated by the TV matrix 22 and displayed on the display 37 is used to position the patient's eye so that its pupil is centered relative to the optical axis of the device. The pupil center is assumed to coincide with the pupil vertex, which is specified by the center of the figure composed of the Purkinje reflection image. The patient is asked to fix his gaze on the image of the target 24. In order to focus the image of the target 24, it is necessary to achieve conjugation of the retinal plane and the target plane by varying the optical power of the fluid lens 18. The lenses 18 and 20 are designed to form a doubly telecentric system, that is, both image space and object space are telecentric within the range of refractive error of the measured eye, usually from minus 10 to plus 10 diopters. If this condition is not met, a scaling factor should be taken into account when calculating the eye's refraction.

[0068] There are two options for adjusting the fluid lens 18 to compensate for the refractive error of the eye: for example, by adjusting it according to the patient's instructions through a device such as a joystick; or by performing preliminary single-beam ray tracing by measuring the defocus component of the Zernike series, that is, turning on the generator 6 (frequency F x1 ) and 8(Frequency F y1 ) and turn off generator 7 (no frequency F x2 ) and 9 (no frequency F y2 ).

[0069] After the fluid lens 18 has compensated for the defocus of the eye, the dual beam procedure begins to determine the position of the eye along the visual axis. The direction toward the deepest point of the central pit is defined for the X and Y coordinates, respectively. For the dual beam split in the X direction, the procedure is as follows. The second driver 5 operates in single beam mode (applying only the frequency F to the crystal). y1 The first driver 4 operates in a dual-beam mode (applying two signals of frequency F to the crystal). x1 and F x2 signal). Using this combination of driver functions, by controlling the frequency F x1 (left side in the figure) and F x2 (right side of the figure), the dual beam splitting in the X direction can be positioned in the central concave area (Figure 9 ) Any point therein. The bisector here is shown as an axis equidistant from the two laser beams. The splitting angle corresponds to the frequency difference ΔF x Correspondingly, when the first driver 4 is in the single-beam mode (only the signal with frequency F x1 is applied to the crystal), and the second driver 5 is in the double-beam mode (signals with two frequencies F y1 and F y2 are applied to the crystal), by controlling the frequencies F y1 and F y2 , the double-beam splitting in the Y direction can be positioned at any point in the fovea centralis region. The angle difference is equivalent to the frequency difference ΔF y . The scattering process of the fundus tissue is as Figure 9 shown. Part of the laser penetrates deep into the tissue where backscattering occurs. The backscattered radiation is detected by the coherent detector 27 after propagation.

[0070] First, using the double beam pointing at the fovea centralis along the patient's line of sight, search for the deepest point of the fovea centralis pit in the X direction. The coherent detector 27 receives the backscattered light through the aperture 28, and the size of the aperture 28 depends on the amount of light (the more the better) and the number of interference fringes (the fewer the better). In fact, its diameter is in the millimeter range. There is a low-pass filter at the output end of the coherent detector 27, thus generating the difference frequency ΔF x at the output end of the detector. The phase difference at this frequency contains information about the path difference between the beams in the X direction. The signal output by the coherent detector is sent to the signal input end of the phase discriminator 29, while the frequency difference unit 30 sends the X reference signal with frequency ΔF x to the reference input end of the phase discriminator 29. The signal proportional to the phase difference is sent to the processing unit 10, and the processing unit 10 calculates the next position where the double beam should be located to obtain the phase difference corresponding to the equal paths of the two beams, which means that their bisector points to the middle of the fovea centralis pit. The process of repositioning the beams takes dozens of microseconds, so the time to adjust the direction of the double beam is less than one millisecond.

[0071] The phase difference y of the frequency ΔF contains information about the path difference between the beams in the Y direction. The signal output by the coherent detector is sent to the signal input end of the phase discriminator 29, and the frequency phase difference unit 30 sends the Y reference signal with frequency ΔF y to the reference input end of the phase discriminator 29. The signal proportional to the phase difference The proportional signal is sent to the processing unit 10, which calculates the next expected position of the two beams to obtain the phase difference corresponding to equal paths of the two beams, meaning that (similar to the X direction) their bisector points to the middle of the fovea in the Y direction. In short, the beam repositioning processes in both directions are limited within a few milliseconds.

[0072] Figures 10A - 10C Shows the search process of the visual axis. Three cases of the plane XOZ are shown in the figure:

[0073] Figure 10A —— The diffraction path of the beam generated by the frequency F x1 on the grating is longer than the diffraction path of the beam generated by the frequency F x2 on the grating, so its phase delay will be longer than the delay The phase difference converted to the frequency ΔF x will be positive This means that the error signals controlling the frequencies F x1 and F x2 should synchronously move the two beams to the left to make the bisector closer to the visual axis. To this end, the processing unit 10 recalculates the measured phase difference as the frequency values F x1 、F x2 to be corrected, and keeps ΔF x unchanged.

[0074] Figure 10B —— The diffraction path of the beam generated by the frequency F x2 on the grating is longer than the diffraction path of the beam generated by the frequency F x1 on the grating, so its phase delay will be longer than the delay The phase difference converted to the frequency ΔF x will be negative This means that the error signals controlling the frequencies F x1 and F x2 should synchronously move the two beams to the right to make the bisector closer to the visual axis.

[0075] Figure 10C —— The diffraction paths of the beams generated by the two frequencies F x1 and F x2 on the grating to reach the opposite slopes of the pit are equal, so their phase delays and will be equal to each other. The phase difference converted to the frequency ΔF x will be equal to zero This means that the bisector coincides with the visual axis. A similar search should also be carried out for the plane YOZ. On this plane, the frequencies F y1 and F y2 will vary while keeping ΔF y unchanged.

[0076] As described above, the frequency difference ΔF x in the X channel and the frequency difference ΔF y in the Y channel are preferably taken to be the same value: ΔF x = ΔF y = ΔF. In this way, the low-pass filters of the two channels can be the same. Otherwise, the output of the coherent detector 27 would need to be able to switch between two different filters. This feature does not affect the principle of the present invention.

[0077] Step 2, measuring the wavefront:

[0078] Determine the dislocation positions X VA , Y VA of the corneal intersection points through the visual axis, and finally measure the refractive power. The laser beam is incident on the eye through the first deflector 2 and the second deflector 3, and is driven by the first driver 4 and the second driver 5, both operating in a single-beam mode, that is, the first driver 4 is only controlled by the first generator 6 (frequency F x1 ), and the second driver 5 is only controlled by the second generator 8 (frequency F y1 ). During the final measurement of the refractive index, the generator 7 (frequency F x2 ) and the generator 9 (frequency F y2 ) are in a silent state. Therefore, no beam splitting is performed. The beam is positioned within the eye aperture in any temporal order and any spatial layout, which is necessary for reconstructing the eye refractive parameters.

[0079] The beam passes along the above path through the lens 11, lens 12, spatial filter (aperture) 14, collimating lens 15, beam splitter 17, fluid lens 18, beam splitter 19, and lens 20 to reach the eye. The lenses 18 and 20 are designed as described above. The conjugate conditions of the retina plane with the sensitive surfaces of the target 24, the coherent detector 27, and the linear array detectors 32 and 33 are also considered. The cylindrical lenses 34 and 35 are used to compress the laser spot image on the retina. At the conjugate positions of the lenses 18 - 20, the image of the spot will be stretched a little in the vertical direction.

[0080] After the laser spot on the retina is imaged on the linear array detectors 32 and 33, its coordinates are determined by the processing unit 10. Based on the knowledge of the coordinates passing through the pupil and hitting the retina and the parameters of the imaging optics, the processing unit 10 can calculate the refractive power parameters of the eye for each point in the pupil. This information is sufficient to reconstruct the two-dimensional distribution of these parameters and the derivative parameters of the eye and display them on the display screen 37.

Claims

1. A method for measuring the human eye wavefront relative to an objectively determined visual axis, comprising: Continuously detect a set of points within the pupil of an eye with a laser beam over time; Detect the radiation backscattered from the retina of the eye; Measure the coordinates of the laser spots on the retina; And Reconstruct the wavefront based on the refractive distribution on the eye pupil; Wherein, the laser beam for detecting the eye is oriented along the visual axis of the eye during the measurement of the wavefront, and the visual axis is determined by the following steps before measuring the wavefront: Split the laser beam into double beams in the X and Y directions respectively; Detect the foveal area of the retina with the double beams in both the X and Y directions of the beam splitting; Detect the laser light backscattered from the foveal area; Measure and compare the phase shifts of the beams in the double beams relative to each other in both the X and Y directions of the beam splitting; Determine the direction of the double beams at the position of equal depth of the relative slopes of the fovea indicated by the zero value of the phase shift between the beams in the double beams; and Designate the visual axis as the bisector of the double beams, and the bisector is located at the position of equal depth of the relative slopes of the fovea in both the X and Y directions of the beam splitting.

2. The method according to claim 1, wherein the beam splitting includes diffraction in a biaxial acousto-optic deflector in orthogonal directions in the pupil plane.

3. The method according to claim 1, wherein There is a depth difference between the relative slopes of the fovea, and the depth difference is defined as the phase difference between the signals obtained by converting the phase difference between the carrier frequencies of the split beams into the frequency difference between the carrier frequencies of the double beams.

4. The method according to claim 1, wherein Use the double beams for detection and change the detection direction until the phase difference values in two orthogonal directions both become zero.

5. A device for measuring the human eye wavefront relative to an objectively determined visual axis, comprising: A laser configured to emit a laser beam with a wavelength suitable for ray tracing; A pair of diffraction-based deflectors composed of acousto-optic crystals, including a first deflector and a second deflector. The first deflector is configured to deflect the laser beam in a first direction orthogonal to the propagation direction of the laser beam, and the second deflector is configured to deflect the laser beam in a second direction orthogonal to the first direction. Both the first deflector and the second deflector in the pair of deflectors have an inlet aperture and an outlet aperture, and both the first deflector and the second deflector in the pair of deflectors are positioned along the path of the laser beam so that the effective deflection centers of the first deflector and the second deflector are substantially coincident; A pair of drivers, including a first driver operably connected to a first frequency generator and a second driver operably connected to a second frequency generator. The first driver and the second driver in the pair of drivers are configured to acousto-optically drive the first deflector and the second deflector respectively; A telescope and a collimating lens, which are optically aligned with the deflection centers of the first deflector and the second deflector in the pair of deflectors in sequence; A first beam splitter disposed on the path of the laser beam to the human eye and the radiation reflected by the human eye; A position-sensitive detector disposed on the path of the radiation reflected by the human eye; And A processing unit operably communicating at least with the laser, the first frequency generator, the second frequency generator, and the position-sensitive detector; Wherein, A third frequency generator configured to be connected to the first driver; A first frequency difference filter, configured to be connected to the first driver, such that a first frequency difference is a difference between frequencies generated by the first frequency generator and the third frequency generator; A fourth frequency generator, configured to be connected to the second driver; A second frequency difference filter, configured to be connected to the second driver, such that a second frequency difference is a difference between frequencies generated by the second frequency generator and the fourth frequency generator; The first frequency difference and the second frequency difference are established to be equal to each other, and the coherence detector is configured with the first frequency difference and the second frequency difference at its output; An electro - controlled conjugate telescope, disposed at an adjustable refractive index position between the first beam splitter and the human eye, such that the plane of the retina is optically conjugate to the plane of the position - sensing detector and the plane of the coherence detector; A coherence detector, disposed on the laser radiation path after the first beam splitter, with an aperture in front of the coherence detector, and a low - pass filter at the output of the coherence detector; A phase discriminator, disposed at the output of the coherence detector, the phase discriminator having two switchable input terminals, namely a first reference input terminal connected to the output of the first frequency difference filter and a second reference input terminal connected to the output of the second frequency difference filter; and The third frequency generator, the fourth frequency generator, the electro - controlled conjugate telescope, and the phase discriminator are operably in communication with the processing unit.

6. The apparatus according to claim 5, wherein the first beam splitter is a polarization beam splitter configured to transmit linearly polarized light from the laser through the polarization beam splitter to the human eye and reflect an orthogonal portion of the depolarized radiation from the human eye and direct it to the position sensing detector and the coherence detector.

7. The apparatus according to claim 5, wherein the position sensing detector is provided with a dual-channel configuration corresponding to a first orthogonal direction and a second orthogonal direction of position measurement.

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