Method and device for measuring intraocular distance and structure through laser ray tracing

Abstract

A method and apparatus for laser ray tracing measurements of intraocular distances and structures are provided herein. Generally, the device has a laser, a pair of acousto-optic deflectors, a driver, a frequency generator and beam splitter, a telescope and collimating lens, a base optometric channel and a processing unit, and is arranged and configured to detect the eye with a modulated laser beam oriented to intersect along an optically determinable path. Analysis of detectable backscattered radiation is used to confirm the position of the beam intersection and to calculate its distance to the corneal vertex. The data obtained by repeated probing is used to reconstruct the intraocular structure of the eye.

Description

[0001] Cross-reference to related applications

[0002] This international application claims priority to U.S. Provisional Application Serial No. 63 / 429,072, filed November 30, 2022, pursuant to 35 U.S. SC §119(e), the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention generally relates to the field of ophthalmic instruments for examining the eye. More specifically, this invention relates to ophthalmic examination instruments for measuring intraocular distances in the eye, particularly intraocular distances related to the lens and its position and the state of its media, which are necessary for diagnosing the eye and calculating parameters for lens replacement. Background Technology

[0004] As we age, the quality of the human eye's lens decreases in terms of opacity and refractive properties, leading to lens dysfunction syndromes. When the degree of degeneration reaches a certain level, it may be necessary to replace the natural lens with an artificial lens (IOL). To properly determine the type of IOL, accurately calculate its power, and pinpoint its location (including the distance to the corneal apex), the anterior chamber depth, i.e., the distance from the anterior surface of the lens to the corneal apex, must be measured. The tilt of the lens relative to the eye's optical axis or visual axis is another important parameter.

[0005] The depth of the anterior chamber can be assessed using a gonioscope with a special lens that contacts the cornea, or using ultrasound with a special acoustic transducer. These procedures are uncomfortable for the patient and not precise enough. Schippert et al. proposed a solution in U.S. Patent No. 6,631,990: combining a triaxially linearly movable interface assembly with a slit lamp to achieve better accuracy. This slit lamp is operable to pick up the movement of the microscope assembly in the optical axis and vertical direction.

[0006] Prior art also discloses optical coherence tomography (OCT) for measuring biometric parameters of the eye, which can be used alone (C. Baker et al., U.S. Patent No. 7,400,410) or in combination with a corneal topography or keratometer (R. Ebersbach et al., U.S. Patent No. 10,694,941). A major problem when combining OCT with other techniques is “stitching together” accurate data from OCT imaging under conditions of relatively rapid eye movement.

[0007] At the same time, methods are known for obtaining information from limited spatial volumes, selected by means of interference coherent light scattered in them. These examples are represented by the laser velocimetry method, in which the scattered light from the limited spatial volume of the intersection of the laser beams is detected and analyzed, converting the interference fringes into light modulation, the modulation parameter being the measurement of the process in the limited spatial volume, the modulation frequency being proportional to the velocity of the moving scattering particles in space (R. Dandliker et al., U.S. Patent No. 3,895,873).

[0008] The method for obtaining information from the limited spatial volume of the intersection of the laser beams has been used for corneal shape measurement (V. Molebny et al., "High precision double-frequency interferometric measurement of the cornea shape", Proc. SPIE, Vol. 2965, pp. 121-126). According to this method, the cornea is laser probed by a pair of double laser beams generated by acousto-optic modulation, resulting in two frequency-shifted laser beams. The backscattered light from the intersection volume of the cornea surface is detected and analyzed, including the carrier frequencies of the two beams, the simultaneous presence of the two beams resulting in a filtered differential frequency at the detection, the parameters of which provide information about the intersection volume.

[0009] In order to apply this method to depth scanning along the Z axis in the intraocular space, it is necessary to find the characteristics, the scheme and the corresponding operation of the laser beams to verify the reception of the backscattered signal from the limited volume. Seeking a solution to this problem is the purpose of the present invention. SUMMARY

[0010] The proposed solution includes a method and a device for laser ray tracing measurement of intraocular distances and structures. The method is based on probing the eye with a combination of laser beams configured to intersect each other inside the eye along optically determinable paths, where the beams are generated from a single laser beam by shifting their carrier frequencies with respect to each other by a frequency offset. The scattered laser light in the volume where the beams intersect each other is detected and analyzed. The frequency offset of the laser carrier frequencies is pre-set in a combination such that the intersection of the beams is confirmed only when a certain frequency is filtered out from the detected backscattered signal. For two beam pairs, their frequency difference is filtered and mixed with each other, resulting in a certain frequency, which can be the sum or the difference of the pair of filtered frequencies. Thus, defining the position and the trajectory of the beam intersection point inside the eye, the distances and the medium structures along the trajectory, as well as the tilt of the lens can be calculated.

[0011] The apparatus implementing the proposed method consists of a laser having a pair of orthogonally deflected acousto-optic deflectors at its output, the deflectors being driven by drivers connected to a generator, the output of the deflectors being directed in turn through a first telescope and a collimating lens into the eye. The generator providing signals to one of the deflectors produces two pairs of signals, the first pair having a first frequency difference and the second pair having a second pair of frequencies. The first pair of frequencies and the second pair of frequencies applied to one of the deflectors produce a pair of double beams. A deflection optical element is placed in front of the eye to direct deflected paths of the double beams directed to the eye at symmetrically inclined angles to measure the distance along the optical axis. When measuring the tilt of the lens, the peripheral distance is measured by having one of the double beams parallel to the optical axis.

[0012] A coherent detector having a low pass filter at its output is placed in the path of the laser radiation backscattered in the eye and is further routed through a beam splitter to the coherent detector. A fluidic lens is mounted in the path of the light to the coherent detector with the function of keeping it conjugate to the intersection point during the measurement. A phase detector is placed at the output of the coherent detector having a low pass filter. The reference signal for the phase detector is generated as a combined frequency which can be the sum or difference of the differential frequencies controlling the two beams of the double beam. A basic refraction channel is also included in the apparatus which contains an optotype, an optical system to position and align the apparatus, and means for measuring the corneal topography and the wavefront characteristics of the eye. BRIEF DESCRIPTION OF DRAWINGS

[0013] For a detailed understanding of the above-mentioned features of the application, a more particular description of the application briefly outlined above will be rendered by reference to the appended drawings. These drawings form a part of the specification. Among the various drawings, like reference numerals are used to indicate like parts throughout the several views. However, it is to be understood that the appended drawings illustrate only preferred embodiments of the application and are therefore not to be considered limiting of its scope.

[0014] Figure 1 The principle of triangulation is shown by intersecting the optotype with two directions symmetric at point A and point B to find the distance.

[0015] Figure 2 The stepwise ray tracing of the beam intersection points L1,... L i ,... L n along the optical axis is shown. The beams a and b are symmetric with respect to the optical axis and are inclined at a constant angle a, the distance between the points of incidence A i and B i on the cornea is b i .

[0016] Figure 3 The case of triangulation is shown in which one of the beams AL is perpendicular to the base AB.

[0017] Figure 4The beam intersection point L on the beam a incident to the eye parallel to the optical axis is shown a1 ai an The step-by-step ray tracing of the beam intersection L

[0018] Figure 5 is a functional diagram of a device embodiment with means for probing the eye with laser beams, detecting backscattered light, converting it into a signal for processing, and obtaining information about intraocular distances and structures from it.

[0019] Figure 6 The intersection of possible laser beam sets capable of measuring intraocular distances in the X0Z and Y0Z planes is shown.

[0020] Figure 7 The compatibility of measuring intraocular distances in the X0Z and Y0Z planes and measuring wavefronts using the central part of the beam path is demonstrated.

[0021] Figure 8 The schematic diagram in Figure 5 shows the beam paths formed by pairs of mirror sets M3, M4 and M5, M6 turned after the axial distance measurement using symmetrically tilted laser beams configured as in Figure 1 and Figure 2 .

[0022] Figure 9 The spectrum of the laser beams projected into the eye is shown. The double beam a has carrier frequencies f a1 and f a2 with a difference F a . The double beam b has carrier frequencies f b1 and f b2 with a difference F b . To ensure the symmetry of the beam tilting, the frequencies f a1 and f b1 (or f a2 and f b2 ) are chosen to be equal to each other. The offset frequency shifts (or differential frequencies) F a and F b are much smaller than the carrier frequencies f a and f b . The frequency f0 is the center frequency of the first order diffraction in the X- and Y-deflectors. It is important that F a is not equal to F b . The solid circles and solid lines indicate the active beams (probing the eye in time sequence). The open circles and dashed lines indicate the off (non-active) beams.

[0023] Figure 10 The schematic diagram in Figure 3 and Figure 4 ​​The paths of the double beams a and b that are turned by the mirror pair M5, M6 in the case of a distance measurement by triangulation configured centrally parallel to the optical axis. If the double beam a is tilted by the mirrors M3, M4 and the double beam b is parallel to the optical axis, the mirror image configuration occurs.

[0024] Figure 11 The signal accumulation process is shown Figure 10 The spectrum of the laser beams that are projected into the eye in the case shown. The double beam a has a constant carrier frequency f a1 and f a2 during the measurement period. b1 The frequency f b2 of the double beam b and the frequency f b are varied during the measurement, the difference F a being constant. The frequency F b is not equal to the frequency F n .

[0025] Figure 12 The signal accumulation process is shown during the measurement, which displays the structure of the eye (by way of example the lens), which begins at the time t1, when the double beam a and the double beam b cross each other at a distance h1 from the vertex of the cornea (corresponding to the front surface of the lens) and ends at a distance h a1a2 from the vertex of the cornea (corresponding to the back surface of the lens). The beam frequency values at the time t1 are designated as {f b1b2 & f t1}. The designation {f a1a2} means that the double beam a has two carrier frequencies f a1 and f a2 . Similarly, the double beam b with the carrier frequency designation {f b1b2} has two carrier frequencies f b1 and f b2 . Cumulatively, at the time t1, the frequencies of the beams a and b are designated as {f a1a2 & f b1b2} t1 . For the times t i and t n , the indices in the brackets are changed to t i and t n , respectively. DETAILED DESCRIPTION

[0026] As used herein, the term "a" or "an" when used in conjunction with the term "comprising" in the claims and / or the specification can mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one." Some embodiments of the application can be implemented by or substantially by one or more elements, method steps and / or methods of the application. It is contemplated that any method described herein can be implemented relative to any other method described herein.

[0027] As used herein, the term "or" in the claims is used to mean "and / or" unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and / or."

[0028] As used herein, "includes" and variants thereof, such as "including," "comprising," and "containing," will be understood to embody the meaning ascribed by the United States Patent Office in either the "final" or "allowable" rule when the words are used in their "Broadest Form" in the examination of any patent application or patent. Similarly, "another" or "other" can refer to at least a second or more, or a component of the same.

[0029] As used herein, the terms "consisting of and "consisting only of are used in the exclusive sense, meaning that additional elements can not be present.

[0030] As used herein, the ordinal adjectives "first," "second," "third," and "fourth" merely denote different instances of a similar object, and do not imply that the objects so described must be in a given order, either temporally, spatially, in rank, or in any other manner.

[0031] As used herein, the terms "including," "containing," and "including but not limited to" are interchangeable with each other.

[0032] In one embodiment of the application, a method for laser light ray tracing measurement of intraocular distances and structures is provided, comprising: probing an eye with laser beams by simultaneously directing at least two modulated laser beams to the eye, the modulated laser beams being directed to cross each other along optically determinable paths; detecting and analyzing backscattered laser radiation to include a combination of the two modulation frequencies, thereby determining the position of the beam crossing point; calculating the distance of the beam crossing point to the corneal vertex; repeating the step of probing the eye by changing the trajectory of the crossing point in the eye, storing the data thus obtained and reconstructing the intraocular structure of the eye, and performing the step of probing the eye in two independent processes in a vertical plane containing the optical axis.

[0033] In this embodiment, the method can include: single sideband modulating each of the laser beams by shifting the carrier frequency of the first laser beam by a first differential frequency to convert it into a first laser doublet, and by shifting the carrier frequency of the second laser beam by a second differential frequency to convert it into a second laser doublet; confirming detection of the beam intersection point by detecting and filtering a combination of the two differential frequencies of backscattered laser radiation from the eye, the combination comprising a sum or difference of the differential frequencies that calculates the distance of the beam intersection point from the vertex of the cornea; storing data from repeated operations and reconstructing the intraocular structure of the eye by repeating the step of probing the eye by changing the trajectory of the intersection point in the eye; and performing the step of probing the eye in two independent processes in a perpendicular plane containing the optical axis. In addition to this embodiment, the method can include deriving the optically determinable path from a corneal topography and ray tracing wavefront measurements. In one aspect of these embodiments, the first laser doublet and the second laser doublet can be symmetrically tilted with respect to the visual axis of the eye. In another aspect, the first laser doublet can be coincident or parallel with the visual axis of the eye; wherein the second laser beam is tilted.

[0034] In another embodiment of the application, there is provided an apparatus for laser ray tracing measurement of intraocular distances and structures in an eye, comprising: a laser configured to emit a laser beam of a wavelength suitable for ray tracing; a pair of acousto-optic deflectors, comprising a first deflector configured to deflect the laser beam in a first plane containing an optical axis and a second deflector configured to deflect the laser beam in a second plane containing the optical axis and perpendicular to the first plane; each acousto-optic deflector of the pair of acousto-optic deflectors has an entrance aperture and an exit aperture and is positioned along the path of the laser beam whereby its effective deflection centers substantially coincide; a first driver having an output operably connected to the first deflector and a second driver having an output operably connected to the second deflector; a first frequency generator having an output connected to the first driver and a second frequency generator having an output connected to the second driver; a telescope and a collimating lens placed in optical alignment with the deflection centers of the pair of acousto-optic deflectors in sequence; a first beam splitter placed in the path of the laser beam to the human eye and on the path of backscattered laser radiation from the eye; a second beam splitter placed after the first beam splitter on the path to the eye; a base optometry channel having an optical axis diverted through the second beam splitter to the eye, the base optometry channel comprising an optotype, a device positioning and alignment system, and a device for measuring corneal topography and wavefront characteristics of the eye; a processing unit with a display, the processing unit being in operable communication with the laser, the frequency generators, and the base optometry channel. In this embodiment, the laser beam propagation area is divided into an inner area and an outer area, wherein the inner area is configured for ray tracing of the eye with the laser beam parallel to the optical axis and the outer area is configured for tilted ray tracing of the eye; an optical element group is placed in the outer area to direct the probe laser beam at a skew angle; the configuration of each of the first and second frequency generators comprises a first oscillator of a first frequency, a second oscillator of a second frequency, a third oscillator of a third frequency, a fourth oscillator of a fourth frequency, and a combined frequency unit, the first frequency and the second frequency having a first frequency offset therebetween defining a spatial split in a first dual beam, the third frequency and the fourth frequency having a second frequency offset therebetween defining a spatial split in a second dual beam, the combined frequency unit combining the first frequency offset and the second frequency offset as a difference therebetween or as a sum, and the configuration of the first and second frequency generators enables a mode of simultaneous operation of all oscillators or a mode of single oscillator operation.In this embodiment, a coherent detector is placed on the backscattered laser radiation path after the first beamsplitter, in front of which there is an aperture; a low pass filter is provided at the output of the coherent detector, which is connected to a processing unit; a phase detector is provided after the low pass filter, the signal input of which is connected to the output of the low pass filter, the reference input of which is connected to the combined frequency unit of the first frequency generator or the second frequency generator when enabled, the output of which is connected to the processing unit; the processing unit is configured to make measurements in the first plane and the second plane, respectively, in its connections with the first frequency generator and the second frequency generator, so that when measurements are made in the first plane, the first, second, third and fourth frequencies from the first frequency generator are connected to the first driver, a single frequency from the second frequency generator is connected to the second driver, and the combined frequencies from the first frequency generator are connected to the reference input of the phase detector; and when measurements are made in the second plane, the first, second, third and fourth frequencies from the second frequency generator are connected to the second driver, a single frequency from the first frequency generator is connected to the first driver, and the combined frequencies from the second frequency generator are connected to the reference input of the phase detector.

[0035] In one aspect of this embodiment, each of the first and second frequency generators can be configured as a first and second four-channel frequency synthesizer with synchronous direct digital synthesis. In another aspect, the first and second frequency generators can be configured as a single eight-channel frequency synthesizer with synchronous direct digital synthesis, where the first four channels thereof are used as the first frequency generator and the last four channels thereof are used as the second frequency generator. In this embodiment and its aspects, the set of optical elements placed in the outer region comprises a first and second set of mirrors, each of the mirror sets consisting of two outward mirrors placed symmetrically with respect to the optical axis and two inward mirrors placed symmetrically, the first set of mirrors being configured to divert the optical path in the first plane and the second set of mirrors being configured to divert the optical path in the second plane.

[0036] The present invention applies the principle of triangulation to measure intraocular distances. For two light beams AL and BL that pass through two points A and B with known coordinates and intersect each other at a third point L, the geometric problem is easily solved. Figure 1The case when the angles in points A and B towards point L are the same and equal to a is shown. The distance h in this case can be defined as h = (b / 2) x tan a. When the path of the light beams passes through different media, the task can still be solved with some a priori knowledge and recommendations related to these media. In the case of the human eye, these media are the cornea, the lens, the anterior chamber and the posterior chamber. The preliminary information on the media can consist of known eye models, measured corneal topography and wavefronts. All this information is related to the prior art and will not be the subject of discussion in this invention.

[0037] Figure 2 The step-by-step ray tracing of the intersection of the light beams along the optical axis of the eye is shown. For simplicity, it is recommended to set the visual and optical axes of the eye to coincide. In addition, the laser beams are represented in the geometric figure as lines, without taking into account their cross-sectional dimensions (including beam multiplication, wavelength or divergence).

[0038] As mentioned above, the light beams a and b are symmetrically tilted at a constant angle a relative to the optical axis, from the axis to the points of incidence A i and B i in the cornea. The distance of the light beams from each other inside the eye along the optical axis at the point L i at a distance h i from the vertex of the cornea C (for simplicity, only three points L1,...L i ,...L n passing through the lens are shown). The height of the point C above points A and B is included in the calculations according to the known curvature of the cornea.

[0039] Using the features provided herein to identify the points of intersection of the light beams L1,...L i ,...L n , their position along the internal path of the eye is calculated and used for further calculations to define the parameters of the intraocular lens to replace the lens and correctly position it during the operation. These calculations are not the subject of this invention.

[0040] With the help of the invention provided herein, not only can intraocular distances be measured along the optical axis, but also along any line specified by the laser beams. In this way, the tilt of the lens can be determined by measuring the distance of the peripheral corneal surface from the lens. Figure 3 The case is shown when one of the angles at the base AB is 90 degrees. The distance h is measured along the light beam coinciding with the straight line AL. The formula for calculating the distance h is h = (a + b) x tan a.

[0041] Figure 4 A time sequence of operations is demonstrated in which the peripheral light beam a parallel to the optical axis remains stationary, while the light beam b changes its position at each interval. The distance of the light beam along the path of the light beam a from the vertex of the cornea C in the eye is hai point L ai (L a1 ,…L ai ,…L an ) intersect each other. Similarly, as in the case of symmetry of the beam tilting, the height of point C above points A and B is included in the calculation according to the known corneal curvature.

[0042] The measurements are taken in each plane XOZ and YOZ, keeping the central frequency f0 of the vertical plane outside the range of frequencies that interfere with the others.

[0043] The specific features of the invention are explained herein by referring to the functional diagram of the device Figure 5 . The laser 1 is attached by its output to the input of the first deflector 2 whose scanning center is in point O x . 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 speed of deflection and scanning, acousto-optic deflectors can be recommended based on the principle of light diffraction on a grating produced by ultrasonic waves in an acousto-optic crystal. For the purposes of the invention, the scanning centers in the vertical (X and Y) directions coincide. In practice, the deflectors 2 and 3 can be designed in such a way that their crystals are as close to each other as possible, on the order of millimeters. To produce a diffraction grating in the crystal, drivers are used, where the first driver 4 connected to the first deflector 2 is used to deflect the laser beam in the Y direction, and the second driver 5 connected to the second deflector 3 is used to deflect the laser beam in the X direction.

[0044] The deflection angle depends on the grating pitch, which is defined by the frequency of the high-frequency signal applied to the transducer used to excite elastic waves in the crystal. This frequency is usually in the range of (but not limited to) 60-80 MHz for deflecting the laser beam in the near infrared. In the device presented herein, only the first order of diffraction in the X and Y directions is used.

[0045] The selection of the first order of diffraction is made by a spatial filter, which is physically an aperture in a non-transparent material. The selected first order beams are scanned within the selection aperture to produce a sequence of directions for probing the eye.

[0046] The drivers 4 and 5 are driven by frequency generators that produce sinusoidal voltages of specific frequencies. The first driver 4 is connected to the output of the first generator 6, while the second driver 5 is connected to the output of the second generator 7.

[0047] When distances and structures in the XOZ plane are measured, the first generator 6 feeds the first driver 4 simultaneously with four different frequencies f1, f2, f3, f4. During these measurements, these four frequencies are varied as described below. The second generator 7 feeds the second driver 5 with only one frequency f0, to keep the light beam in the plane XOZ. The frequency f0 is the central frequency of the first order diffraction in the X and Y deflectors.

[0048] Similarly, when distances and structures in the YOZ plane are measured, the second generator 7 feeds the second driver 5 simultaneously with four different frequencies f1, f2, f3, f4. During this measurement cycle, although the four frequencies are also varied in each probe, the first generator 6 feeds the first driver 4 with only one frequency f0 during the whole cycle, to keep the light beam in the plane YOZ. The value of f0 is due to any one of the four frequencies f1, f2, f3, f4.

[0049] At the periphery of the laser beam path in the XOZ and YOZ planes, optical components are placed, which divert the laser beam twice: outwards, and then inwards Figure 5 Because the measurements of intraocular distances and structures are made with a laser beam whose diameter does not exceed 1 mm in the planes XOZ and YOZ, these components can be mirrors of small width. The beam tilts necessary for triangulation are achieved by two sets of mirrors: 17-18 (M3-M4) and 19-20 (M5-M6) for each plane, respectively.

[0050] To facilitate alignment, the pairs of mirrors 17-18 (M3-M4) and 19-20 (M5-M6) can be implemented as pyramidal faces, or as conical mirrors of an axicon.

[0051] Figure 6 The beam cross-section layout at the entrance to the eye is shown in Fig. 1. For further description, the left and lower wings of the layout are designated as "a" beams, and the right and upper wings as "b" beams. Their number along the X and Y axes (beam density) depends on the spatial resolution required for the structure measurement. The operation of the laser ray tracing of the present invention is compatible with the operation of wavefront measurements requiring the use of a beam path central region as shown in Fig. 2. Figure 7

[0052] The task of the four-frequency generator is to form two pairs of laser beams (or, in other words, double-beam pairs). For example, the first pair f1, f2 forms the "a" double-beam, and the second pair f3, f4 forms the "b" double-beam. The beams formed by them represent the frequencies f1, f2, f3, f4 as f a1 = f1, f a2 = f2, f b1 = f3, f b2 ​= f4. The differential frequencies of these frequency pairs are F1 = F a = f1 - f2 and F2 = F b = f3 - f4. The frequencies F1 and F2 (further also referred to as frequency shifts) are much smaller than the frequencies f1, f2, f3, f4. It is important that F1 is not equal to F2. Having a difference f a = f1 - f2 and f a1 = f3 - f4. a2 = f1 - f2 and f b = f3 - f4. b1 = f1 - f2 and f b2 = f3 - f4. are used for the XOZ and YOZ planes.

[0053] The embodiments of the first frequency generator 6 and the second frequency generator 7 are identical. Each of them comprises four oscillators producing specific frequencies that are fed to the drivers 4 and 5, respectively: a first oscillator 6a produces a first frequency f1, a second oscillator 6b produces a second frequency f2, a third oscillator 6c produces a third frequency f3, and a fourth oscillator 6d produces a fourth frequency f4. The first oscillator (7a), the second oscillator (7b), the third oscillator (7c), and the fourth oscillator (7d) of the second generator 7 produce the same frequencies f1, f2, f3, f4. The frequency generator 6 further comprises a combination frequency unit 6e connected to the oscillators 6a, 6b, 6c, and 6d. Similarly, the frequency generator 7 further comprises a combination frequency unit 7e connected to the oscillators 7a, 7b, 7c, and 7d. Each of these combination frequency units (6e and 7e) delivers a combination of frequencies from the above-mentioned oscillators, i.e. [(f1 - f2) - (f3 - f4)] or [(f1 - f2) + (f3 - f4)]. For distinction, the name of the frequency difference AF = [(f1 - f2) - (f3 - f4)] is used in the figures.

[0054] The drivers 4 and 5 can operate in two modes: a wavefront measurement mode and an intraocular distance and structure measurement mode. In the wavefront measurement mode, the first driver 4 and the second driver 5 control the deflectors 2 and 3, respectively, with only one frequency (e.g. the deflectors 2 and 3 are controlled with the first frequency f1 ), in which mode the first frequency f1 will be f x1 for the X channel and f y1 for the Y channel.

[0055] The measurement pattern of intraocular distances and structures consists of two processes, the first of which is performed for the XOZ plane and the second for the YOZ plane. In the first process, the second deflector 3 keeps the light beam unsplit in the Y direction, while the first deflector 2 splits the input laser beam into two pairs of double beams, the frequencies f1, f2, f3, f4 having the mutual relationship as described above. In the second process, the first deflector 2 keeps the light beam unsplit in the X direction, while the second deflector 3 splits the input laser beam into two pairs of double beams, the frequencies f1, f2, f3, f4 having the same mutual relationship, also as described above.

[0056] The laser light output from the second deflector 3 is directed into a telescope created by two lenses 8 (L1) and 10 (L2). The path of the laser beam into the eye is indicated by the cross-hatched arrow. In order to make the design more compact, a mirror 9 (M1) turns the light path between lenses 8 and 10. The scanning center O x and O y of each of the deflectors 2 and 3 is transferred into the space after lens 10. In the case where the O x and O y axes are made to coincide or are spaced from each other to the extent that it is negligible, then the scanning center after lens 10 is designated as O, which coincides with the back focal point of lens 10. In the space of the diffracted beam, its position must coincide with the direction of the first order of diffraction, both in the X and Y directions. The selection of the first order of diffraction is provided by an aperture 11 (Al), which is a hole whose size is smaller than the distance between the orders of diffraction, in practice, its diameter is of the order of millimeters. The center of this aperture coincides with the point O.

[0057] The next optical element on the path of the laser beam is a collimating lens 12 (CL). Its front focal point coincides with the back focal point of lens 10, so that the scanning center O is located at the center of aperture 11 (Al), which acts as a spatial filter-selector of the first order of diffraction and produces a parallel beam at the exit of lens 12.

[0058] A mirror 13 (M2) turns the direction of the beam towards a first beam splitter 14 (BS1) and, after passing through a second beam splitter 15 (BS2), towards the eye 16. The first beam splitter 14 (BS1) is preferably a polarization beam splitter. It enables the vertically polarized light to continue along its path to the eye. The action of the first beam splitter 14 also includes reflecting the polarization component of the light scattered back from the eye that is perpendicular to the polarization of the initial laser light. These polarization features are illustrated by the inset near the beam splitter 14, which shows the polarization states of the laser "incident light" and the scattered laser "exit light".

[0059] The mutual positioning of the device and the patient's eye and any other necessary alignment is performed using the base optometry channel 21. For these purposes, the Purkinje reflections are provided by several light-emitting diodes (LEDs), Figure 5 Two of them, 22a and 22b, are shown in the middle. The beamsplitter 15 reflects the light scattered back from the eye, including these Purkinje images. The optometry details, which are well known in the art and are not related to the design or the principles of the present invention, are not discussed here.

[0060] For detecting the laser beam interference inside the eye, a coherent detector 25 is installed on the light path indicated by the hatched arrow, which goes from the eye 16, through the beamsplitter 15, is turned by the beamsplitter 14, and goes through the fluid lens (FL) 23 and the aperture 24 (A2). The coherent detector 25 is connected at its output to a low-pass filter 26, which is adjusted for passing the frequency AF, which is equal to the difference of the two frequencies: AF = F a –F b The coherent detector combines the frequencies fl, f2, f3, f4 as a nonlinear component. Considering that the magnitudes of the frequencies fl, f2, f3, f4 are 60 MHz, and the difference between any one of fl, f2 and any one of f3, f4 is in the order of MHz, it is an easy task to select the differences Fl = fl - f2 and F2 = f3 - f4, as it can be much lower. This means that only the frequencies Fl = fl - f2 and F2 = f3 - f4 are used to produce their difference AF = Fl - F2. The combination of the sum of Fl and F2 is also possible, as described in the description of the frequency generators 6 and 7.

[0061] The low-pass filter 26 has two outputs. One of them is connected to the processing unit 27 by the amplitude V of the signal with the frequency AF, which transfers the information on the level of scattering in the area of the beam crossings a and b to the processing unit. The other output is connected to the signal input of the phase detector 28. The reference input of the phase detector 28 is connected to the combined frequency units 6e and 7e, each of which is able to deliver a reference signal with the frequency AF when given permission from the processing unit 27. The signal from the combined frequency unit 6e is enabled when measuring the intraocular distances and structures in the first plane XOZ. The signal from the combined frequency unit 7e is given permission when measuring the intraocular distances and structures in the second plane YOZ.

[0062] The output of the phase detector 28 includes the phase difference between the initial oscillations of the frequency AF from the output of the filter 26 and the same frequency derived from the combination of all four frequencies that interfere at the intersection point in the eye (this signal is transferred from the filter 26 to the phase detector 28) Information. Note that if both frequencies F1 and F2 are present in the signal, i.e., only when the signal originates from the intersection region of beams a and b, frequency ΔF can be extracted solely from the combination of detected signals. This phase difference reveals information about the refractive inhomogeneities encountered by the laser beam on its path to the intersection. During measurement, the path changes, the inhomogeneity changes, and by comparing each trajectory during the measurement, it can be shown how much the structure of the refractive inhomogeneities affects the image quality formed on the retina. This statistical analysis of inhomogeneity can disregard the beam path spread caused by the cornea. An important issue that still needs to be considered is that the trajectories must be closely adjacent to each other, rather than having jumps exceeding 360 degrees from one trajectory to another.

[0063] When along Figure 2 When measuring distance along the optical axis shown, for Figure 1 In the triangulation case shown, the beam path in the device is... Figure 8 As shown. Since the measurement operations in the XOZ and YOZ planes are identical, this paper only describes one of the XOZ planes. After finding the axis of symmetry and determining the refraction parameters, deflector 3 is set to maintain the value of coordinate Y equal to zero by applying frequency f0 throughout the entire period of measuring distance along the optical axis. Simultaneously, deflector 2 is fed by four frequencies, f... a1 and f a2 Frequency pairs form a, f b1 and f b2 The frequency pairs form a double beam b. Both frequency pairs simultaneously strike the aperture of the eye, such as... Figure 2 The beam enters the eye at an angle, which is the angle of the beam a. i Reflected by mirrors M3 and M4 and beam b i The result of reflection by mirrors M5 and M6. During the brief time interval t... i In the middle (typically less than 10 μs), deflector 3 will deflect the dual beam (a i And bi) remains at the i-th position. During this time interval, the coherent detector 25 determines the level of the signal with frequency ΔF. In the next time interval, frequency f a1 -f a2 and f b1 -f b2 The settings are altered to place beams a and b at the (i+1)th position. Figure 8 In the diagram, numbers 1 to n represent consecutive positions during the time interval. The initial time interval t1 and the final time interval t2 are used to acquire information from intersections along the optical axis. n It can be positioned in front of and behind the intraocular lens. Frequency difference F a and F bIt remains constant during the entire cycle (from the first time interval to the last nth time interval). Due to the parallel path of the light beams after the collimating lens 12, the angle a also remains constant during the entire cycle. The segments of the light beams are indicated in Figure 8 Fig. 3 in small circles, which are filled when the light beam is activated during the ith interval, and are open for light beams that are switched off during this interval. The signal level at the exit of the coherent detector 25, as a function of the sequence of time intervals, shows the distribution of the light scattering in the intraocular medium along the optical axis. The phase difference at the exit of the phase detector 28 can be used as a vernier for measuring the intraocular distance under the condition of a phase discontinuity in the sequence of time intervals.

[0064] Figure 9 Fig. 4 shows the spectral dynamics during the measurement with the configuration of Figure 8 Fig. 5. During any time interval t1,...t i ,...t n , both double light beams maintain a constant frequency difference F a = f a1 -f a2 and F b = f b1 -f b2 , and maintain a constant frequency difference AF = F a -F b , and the condition remains F a ≠ F b .

[0065] With the present invention, it is possible not only to measure the intraocular distance along the optical axis, but also along any line specified by the laser beams. In this way, by measuring the distance of the corneal surface at the periphery of the lens, the tilt of the lens is determined. Figure 10 Fig. 6 shows the case where one of the angles of the base AB is equal to 90 degrees, as indicated in Figure 3 Fig. 7. The distance h is measured along the light beam that coincides with the straight line AL. This line coincides with the optical axis, or, as indicated in Figure 4 Fig. 8, it can be at a distance from the optical axis.

[0066] Figure 10 Fig. 9 demonstrates a time sequence in which the light beam a does not move parallel to the optical axis during the measurement cycle, while the light beam b changes its position interval by interval during the same measurement cycle. Figure 10 The crossing of the light beams shown in Fig. 10 has the same names as in Figure 8 Fig. 3. The circles are filled when the light beam is activated during the ith interval, and are open for light beams that are switched off during this interval.

[0067] Figure 11 The spectral composition is explained. It is identical to Figure 9The spectral composition of the light beams a and b differs by the frequency f a1 and f a2 are constant values. Only the scanning beam b is swept to intersect the beam a at different depths (distance from the cornea).

[0068] To measure the tilt of the lens, distances are measured in two perpendicular planes XOZ and YOZ. Multiple distances from the cornea to the point L a1 are measured symmetrically in the opposite peripheral regions of the beam path Figure 4 . The solution is given by measuring the distances in the planes XOZ and YOZ. Other combinations of measured distances in the two planes are used to calculate the tilt. The intraocular distances are measured or calculated with respect to the vertex of the cornea. The determination of the vertex can be provided by a corneal topography, usually combined with a wavefront measurement. When the topography and wavefront measurement are performed, a correction factor is calculated or simply taken from a table reconstructed with ray tracing optical programs like Zemax. This correction factor defines the degree of physical shortening of the intraocular distances compared to the distances in air. These tables are preprogrammed and available as a library in the processing unit 27.

[0069] The functions of the oscillators 6a, 6b, 6c, 6d and of the combined frequency unit 6e, as well as the functions of the oscillators 7a, 7b, 7c, 7d and of the combined frequency unit 7e, can be implemented using the principles and techniques of direct digital synthesis (DDS). Two pairs of software-controlled frequencies, each pair having a constant difference, can be generated in a chip (for example AD9958 or AD9959), whose DDS kernel provides independent frequency, phase and amplitude control on each of the two or four channels and provides phase synchronization of multiple chips. Therefore, the control of the two axes X and Y can be performed in more than two chips.

[0070] When measuring the intraocular distances, the sensitive surface of the coherent detector 25 must be conjugated to the point (microvolume) where the beams cross. This means that the control voltage of the fluid lens 23 is synchronized with the position of the laser beams during the distance measurement period. The synchronization conjugation is performed by bus communication of the lens 23 with the processing unit 27. The processing unit 27 also provides the necessary control commands to the laser 1, to the frequency generators 6 and 7, to the basic optometry channel 21, to the light-emitting diode 22 and requests feedback. The information received from the components of the device after processing is displayed on the display 29.

[0071] Figure 12 The procedure of signal accumulation is shown. Using the triangulation method and based on the configuration of the optical system, the beam frequency groups f a1 , f a2 (specified as f a1a2 ) and f b1 , f b2(f b1b2 ). These frequencies define the two double-beam optical paths and the position of their intersection point. The detection of the signal of frequency difference ΔF = F a -F b (where F a = f a1 -f a2 and F b = f b1 -f b2 ) confirms the detection from the intersection point. In Figure 12 , three points along the optical axis are shown: the first intersection point corresponds to the instant t1, at which the frequency set {f a1a2 , f b1b2} t1 , and after filtering the frequency ΔF in the filter 26, the coherent detector 25 (see Figure 5 ) outputs the signal V to the processing unit 27. The same procedure is applied to instants t a1a2 and t b1b2 with the frequency sets {f ti , f a1a2} b1b2 and {f tn , f i} n . The amplitude of the signal depends on the level of signal scattering in the intersection point, thus defining the boundary of the crossed medium and surface. In the case of Figure 12 , they are the anterior surface of the lens (for t1), the internal medium of the lens (for t i ) and the posterior surface of the lens (for t n ). All this data is accumulated in the processing unit 27 and can be displayed in any convenient form (for example, as a signal variation along the intersection point trajectory).

Claims

1. A method for laser light ray tracing measurement of intraocular distances and structures in an eye, comprising: probing the eye with laser beams by directing at least two modulated laser beams simultaneously into the eye, the modulated laser beams being directed to cross each other along optically determinable paths; detecting and analyzing backscattered laser radiation to include a combination of two modulation frequencies, thereby determining the position of a beam crossing point; calculating the distance of the beam crossing point to the corneal vertex; repeating the step of probing the eye by changing the trajectory of the crossing point in the eye, storing the data thus obtained and reconstructing the intraocular structure of the eye, and performing the step of probing the eye in two independent processes in a perpendicular plane including the optical axis.

2. The method according to claim 1, comprising: single sideband modulating each of the laser beams by shifting the carrier frequency of a first laser beam by a first differential frequency to transform the first laser beam into a first laser doublet and by shifting the carrier frequency of a second laser beam by a second differential frequency to transform the second laser beam into a second laser doublet; confirming the detection of the beam crossing point by detecting and filtering a combination of the two differential frequencies of the backscattered laser radiation from the eye, the combination including the sum or difference of the differential frequencies; calculating the distance of the beam crossing point to the corneal vertex; repeating the step of probing the eye by changing the trajectory of the crossing point in the eye, storing the data from the repeated operation and reconstructing the intraocular structure of the eye, and performing the step of probing the eye in two independent processes in a perpendicular plane including the optical axis.

3. The method according to claim 2, further comprising deriving the optically determinable paths from a corneal topography and a ray tracing wavefront measurement.

4. The method of claim 2, wherein, the first laser doublet and the second laser doublet are symmetrically tilted with respect to the visual axis of the eye.

5. The method of claim 2, wherein, the first laser doublet is coincident or parallel to the visual axis of the eye; wherein the second laser beam is tilted.

6. A laser light ray tracing measurement device for intraocular distances and structures in an eye, comprising: a laser configured to emit a laser beam of a wavelength suitable for light ray tracing; a pair of acousto-optic deflectors including a first deflector configured to deflect the laser beam in a first plane including an optical axis and a second deflector configured to deflect the laser beam in a second plane including the optical axis and perpendicular to the first plane, each acousto-optic deflector in the pair of acousto-optic deflectors having an entrance aperture and an exit aperture and each acousto-optic deflector being positioned along the path of the laser beam whereby its effective deflection center substantially coincides; a first driver having an output operably connected to the first deflector and a second driver having an output operably connected to the second deflector; a first frequency generator having an output connected to the first driver and a second frequency generator having an output connected to the second driver; a telescope and a collimating lens placed in sequence in optical alignment with the deflection centers of the pair of acousto-optic deflectors; a first beam splitter placed in the path of the laser beam to the human eye and backscattered laser radiation from the eye; a second beam splitter placed in the path to the eye after the first beam splitter; a basic optometry channel placed with the optical axis diverted to the eye through the second beam splitter, the basic optometry channel comprising an optotype, a positioning and alignment system of the device and a device for measuring the corneal topography and wavefront characteristics of the eye; and a processing unit with a display, the processing unit being in operable communication with the laser, the frequency generator and the basic optometry channel; wherein: a laser beam propagation zone is divided into an inner zone and an outer zone, wherein the inner zone is configured for ray tracing of the eye using a laser beam parallel to the optical axis and the outer zone is configured for oblique ray tracing of the eye; a set of optical elements is placed in the outer zone to direct the probe laser beam at a deviated angle; the configuration of each of the first frequency generator and the second frequency generator comprises: a first oscillator of a first frequency, a second oscillator of a second frequency, a third oscillator of a third frequency, a fourth oscillator of a fourth frequency and a combined frequency unit, the first frequency and the second frequency have a first frequency offset therebetween, the first frequency offset defining a spatial split in a first dual beam, the third frequency and the fourth frequency have a second frequency offset therebetween, the second frequency offset defining a spatial split in a second dual beam, the combined frequency unit combines the first frequency offset and the second frequency offset as a difference therebetween or a sum thereof, and the configuration of the first frequency generator and the second frequency generator enables a mode of simultaneous operation of all oscillators or a mode of single oscillator operation; a coherent detector is placed in the path of backscattered laser radiation after the first beam splitter, with an aperture in front of the coherent detector; a low pass filter is placed at the output of the coherent detector, the low pass filter being connected to the processing unit; and a phase detector is placed after the low pass filter, a signal input of the phase detector being connected to the output of the low pass filter, a reference input of the phase detector being connected to the combined frequency unit of the first frequency generator or the second frequency generator when enabled, an output of the phase detector being connected to the processing unit; the processing unit is configured in its connection to the first frequency generator and the second frequency generator to provide measurements in the first plane and the second plane, respectively: when providing measurements in the first plane, the first frequency, the second frequency, the third frequency and the fourth frequency from the first frequency generator are connected to the first driver, a single frequency from the second frequency generator is connected to the second driver, a combined frequency from the first frequency generator is connected to the reference input of the phase detector, and when providing measurements in the second plane, the first frequency, the second frequency, the third frequency and the fourth frequency from the second frequency generator are connected to the second driver, a single frequency from the first frequency generator is connected to the first driver, a combined frequency from the second frequency generator is connected to the reference input of the phase detector. When providing the measurement in the second plane, the first frequency from the second frequency generator, the second frequency, the third frequency and the fourth frequency are connected to the second driver, a single frequency from the first frequency generator is connected to the first driver, the combined frequencies from the second frequency generator are connected to the reference input of the phase detector.

7. The apparatus of claim 6, wherein, Each of the first frequency generator and the second frequency generator are configured as a first four-channel frequency synthesizer and a second four-channel frequency synthesizer with synchronized direct digital synthesis.

8. The apparatus of claim 6, wherein, The first frequency generator and the second frequency generator are configured as a single eight-channel frequency synthesizer with synchronized direct digital synthesis, wherein the first four channels thereof are used as the first frequency generator and the last four channels thereof are used as the second frequency generator.

9. The apparatus of claim 6, wherein, The set of optical elements placed in the outer region comprises: a first set of mirrors and a second set of mirrors, each of the sets of mirrors consisting of two outward mirrors placed symmetrically with respect to the optical axis and two inward mirrors placed symmetrically, the first set of mirrors being configured to turn the optical path in a first plane, the second set of mirrors being configured to turn the optical path in a second plane.

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