WO2003057008A2

WO2003057008A2 - Device for measuring the aberration refraction

Info

Publication number: WO2003057008A2
Application number: PCT/US2002/041853
Authority: WO
Inventors: Vasyl V. Molebny; Lamar Frederick Laster; Eugene Smirnov; Leonid Ilchenko; Sergiy Kolenov
Original assignee: Tracey Technologies, Llc
Priority date: 2002-01-02
Filing date: 2002-12-31
Publication date: 2003-07-17
Also published as: AU2002367322A8; UA66936C2; WO2003057008A3; AU2002367322A1

Abstract

High-accuracy measurement of aberration refraction of the eye is needed in optometry for advanced investigation of vision and in refraction surgery for high quality laser-based operations of vision correction. Device contains a probing channel, (1) a measuring channel (2) and a channel of positioning, (3) orientation and providing an accommodation state of the eye. The probing channel is being composed of a laser, (6) two one-coordinate deflectors, (7) and (8) selector the first order of diffraction and collimating lens, which are arranged in series. The exit pupil of selector is coincided with front focus of collimating lens. Transferring telescope of the equivalent center of rays deflection by the first deflector in the equivalent center of rays deflection by the second deflector is placed between acousto-optic crystals of singlecoordinate deflectors. The entrance pupil of transferring telescope and the entrance pupil of selector of the first order of diffraction coincide with equivalent center of beams deflection by acousto-optic crystals of the second deflector. Measuring channel includes a objective lens, position-sensitive photo detector, which is placed in its focal plane, whose output is linked to a unit for information processing and display on the basis of a computer.(22).

Description

DEVICE FOR MEASURING THE ABERRATION REFRACTION OF THE EYE

BACKGROUND OF THE INVENTION

The present invention relates to medical equipment, in particular to diagnostic measuring instrumentation, which can be used for high-accuracy optometric investigations of vision and in refraction surgery for high quality laser-based operations of vision correction. Devices for investigation of aberrations of the optical system of an eye as a function of spatial pupil coordinates are known. The most widely used are four such devices. For parallel (in time) measurement of wave aberrations, which can be later converted into aberration refraction, measurement of wave front structure is used at the exit of the eye by means of partitioning this structure into sub apertures (D. R. Williams, et al. Rapid, Automatic Measurement of The Eye's Wave Aberrations. US Patent 6199986. Int. Cl. A61B 3/10, 13.03.2001). Sub apertures are created using a matrix of coaxial lenses and a matrix of position-sensitive photo detectors is installed in their foci. The wave front is reconstructed from its measured tilts in separate sub apertures. Difficulties in identification of some components of the focal spots structure result in narrower spatial resolution, and consequently in narrower dynamic range of the measured aberrations (that does not exceed + 3 dioptres).

Another device, in which measurements are taken simultaneously for all points of the entrance pupil, is aberrometer based on Chering's principle (M. Mrochen, et al. Principles of Tscherning aberrometry. Journal of Refractive Surgery. 2000, Vol. 16, pp. 570-571). In this device the matrix of diaphragms, which forms regular light pattern, projected onto retina, is positioned in front of investigated eye. Images of distorted by aberrations light pattern on the retina are received using TV camera, they define aberration parameters of optical systems of the eye. In addition to disadvantages of technical nature, typical for parallel in time measurement at the entire entrance aperture of the eye (difficulties with identification of some details of the distorted regular light pattern), this device has a fundamental disadvantage: measured distribution of aberrations is inadequate to the distribution formed by in-focus beam of rays. One of the devices, which uses successively in time analyses, is aberrometer of Nidek company, in which skiascopic principle is used. Moving cylinder has slots, through which a set of light strips is projected on retina. Light backscattered from retina is detected by a set of photodetectors. Characteristics of refraction are determined from temporal dependencies in the detected pulse signals. (S. MacRae, et al. Slit skiascopic-guided ablation using the Nidek laser. Journal of Refractive Surgery. 2000, Vol. 16, pp. 576-580). The drawback of this technique is in the difficulty of its realization requiring a large number of movable mechanical parts and still having low resolution of measurements.

The ray tracing principle for the successive in time analysis is used in refraction aberrometer (V. V. Molebny, et al. Device for Measuring Aberration Refraction of The Eye. Patent Application of Ukraine No. 98105286, Int. Cl. A61B 3/00, A61B 3/10, A61B 3/14, filed Oct. 7, 1998). It contains a probing channel, a measuring channel and a channel of positioning, orientation and providing an accommodation state of the eye (abbreviated: channel of positioning). The probing channel being composed of a laser, two single- coordinate deflectors, selector of the first order of diffraction and collimating lens, which are arranged in series. The selector is designed in accordance with a Kepplerian scheme as a telescope with aperture diaphragm, set at the point of foci coincidence of entrance and exit lenses. The point of the front focus of collimating lens is located in the plane of the exit pupil of the telescope. Each single-coordinate deflector includes a acousto-optic crystal, controlled by a digital frequency synthesizer through output amplifier-driver. Polarization beam splitter, whose orthogonal exit is directed toward the measuring channel, is set after collimating lens in front of the patient's eye. The measuring channel includes a objective lens, which is placed in its focal plane of the position-sensitive photodetector, whose output is linked to a unit for information processing and display on the basis of a computer, connected to a laser, deflectors and a channel of positioning, that performs the functions of the device control. The measuring channel performs the functions of positioning and orientation of patient's eye, setting and control of its accommodation state and calibration of the measuring channel.

The telescope is positioned from deflectors at a distance, corresponding to the coincidence of its entrance pupil and the zone between the single-coordinate deflectors. The field diaphragm is set at the telescope exit, in the plane of its exit pupil, in such way, that it is also located at the point of front focus of collimating lens.

In this device the entrance aperture of the eye is scanned by a narrow laser beam in parallel to the line of patient's sight, and coordinates of its projection on the patient's retina are measured successively in time. A map of refraction errors is reconstructed from these data.

A common disadvantage of this device is its principal incapability to create conditions for beams entering the patient's eye parallel for all points of the entrance aperture of the eye.

Consequently the error in the form of cylindrical astigmatism occurs as a result of measuring the refraction aberrations, wherein value and distribution of this error at the entrance aperture depends on the position of a collimating lens relative to the exit pupil of the telescopic system of selector of the first order of diffraction. The size of this error may reach 2 dioptres, that is insufficient for accurate device. Reducing the error (even not reducing it to zero) is very complicated task. Its compensation by means of software becomes complicated due to individuality for every device.

In addition, when radiation is suppressed in these diffraction orders, which are not used for scanning, conditions for secondary parasitic radiation scattering of diffraction orders, which are not used and whose primary original is light scattering on the constructions of the aperture diaphragm, as a rule, are created inside and outside of the selector construction by means of special filter in the form of aperture diaphragm, placed in the point of foci coincidence of entrance and exit lenses of selector.

SUMMARY OF THE INVENTION

A purpose of this invention is to exclude the error in the form of cylindrical astigmatism from results of measurement of aberrations refraction by creating the conditions for beams entering the patient's eye parallel for all points of the entrance aperture of the eye.

The aforementioned task is solved in a such way: in device for measuring the aberration refraction of the eye, which contains a probing channel, a measuring channel and a channel of positioning, where a probing channel comprises of arranged in series laser, the first and the second diffraction single-coordinate deflectors, selector of the first order of diffraction and collimating lens, where selector of the first order of diffraction is designed as a telescope in accordance with a Kepplerian scheme with aperture diaphragm, set at the point of foci coincidence of the entrance and exit lenses, the point of the front focus of collimating lens is set in the plane of the exit pupil of telescope, each single-coordinate deflector comprises of acousto-optic crystal, controlled by digital frequency synthesizer through output amplifier-driver, the polarization beam splitter, whose orthogonal output is oriented on the measuring channel, is placed after collimating lens in the front of the patient's eye, and the measuring channel comprises of objective lens, position- sensitive photodetector, which is placed in its focal plane of the position-sensitive photodetector, whose output is linked to a unit for information processing and display on the basis of a computer, which performing the functions of the device control, connected to a laser, deflectors and a channel of positioning, the telescope for transferring the equivalent center of beams deflection by the first deflector into the equivalent center of beams deflection by the second deflector is placed between acousto-optic crystals of single-coordinate deflectors in such a way, that the entrance pupil of transferring telescope coincides with equivalent center of beams deflection by acousto- optic crystals of the first deflector, and the exit pupil of transferring telescope and the entrance pupil of selector of the first order of diffraction coincides with equivalent center of beams deflection by acousto-optic crystals of the second deflector.

Furthermore, adding the transferring telescope of equivalent center deflection creates conditions for additional suppression of zero and higher orders of diffraction. We will consider as zero order of diffraction all orders of diffraction, in which radiation does not deflect at least in one axis. This task is solved by designing transferring telescope in accordance with a Kepplerian scheme and adding in it the aperture diaphragm, placed in the point of focus coincidence of entrance and exit lenses of transferring telescope.

Furthermore, more effective suppression of zero and higher orders of diffraction is reached by designing the aperture diaphragm of transferring telescope in the form of slot, whose longer side is oriented along the direction of beams deflection by the first deflector. Slot configuration of aperture diaphragm instead of circular reduces area, through which parasitic diffraction side lobes may pierce the exit of deflector.

Additionally, as a variant of transferring telescope design, cylindrical lenses, whose meridian axis is oriented along the direction of beams deflection by the first deflector, are used in it.

In addition, further improvement in the effectiveness of radiation suppression of these diffraction orders, which are not used for the surface scanning (zero and higher orders of diffraction), may be reached, if light catchers, for example in the form of light-absorbing coating, which impinge at right angle, are installed in transferring telescope and in the selector of the first order of diffraction around the aperture diaphragms outside of the zone of the first order of diffraction of both directions of light beams deflection.

Thus, since the equivalent center of beams deflection by the first deflector is placed into the equivalent center of beams deflection by the second deflector, centers of beams deflection in both directions coincide. This enabled exclusion of undetermined position of the front focus of collimating lens at the exit pupil of the selector, which in analogue corresponds to the zone between the equivalent centers of deflection, different for orthogonal deflection directions. In the invention the exit pupil of the selector corresponds to the coincided center of beams deflection in both directions, since the entrance pupil of the telescopic system of selector is located not in the extensive zone between the equivalent centers of beams deflection of two crystals (that in absolute measurement has the value about 20-30 mm), but exactly coincided with equivalent center of beams deflection by the second crystal, where equivalent center of beams deflection by the first crystal is also placed.

In addition, the double suppression of the scattered parasitic radiation, which corresponds to zero and higher orders of diffraction, is achieved in the invention by adding of aperture diaphragm in transferring telescope, which in one of the variants includes cylindrical lenses, by designing the aperture diaphragm in the form of a slot and inserting the light catcher for radiation of zero and higher orders of diffraction.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention is illustrated by drawings including 14 figures.

FIG. 1. Functional schematic diagram of the device for measuring aberration refraction of an eye

FIG. 2. Map of the phase front distortion by the patient's eye: colour spectrum corresponds to the different front deflections from flat (in micrometers).

FIG. 3. Map of aberration refraction of the patient's eye: colour spectrum indicates different local deflections of the optical power of the eye (in dioptres) from the value, which corresponds to the emmetropic eye.

FIG. 4. Course of rays in the probing channel in case of the tray deflection by crystal of the first deflector in the direction X.

FIG. 5. Course of rays in the probing channel in case of tray deflection by crystal of the first deflector in the direction Y.

FIG. 6. Displacement by telescopic system of the selector of deflection center of parallel light beam from equivalent deflection center by the first deflector when transferring telescope is not used (the entrance pupil of the selector is located in the gap between crystals).

FIG. 7. Projection of the light beam on emmetropic eye in the case, illustrated in FIG 6, when the center of beam deflection is located ahead the front focus of collimating lens (error in the myopia detection). FIG. 8. Displacement by telescopic system of the selector of deflection center of parallel light beam from equivalent deflection center by the second deflector when transferring telescope is not used (the entrance pupil of the selector is located in the gap between crystals).

FIG. 9 Projection of the light beam on emmetropic eye in the case, illustrated in FIG. 8, when the center of beam deflection is located behind the front focus of collimating lens (error in hyper myopia detection).

FIG. 10. Distortion of the measured wave front for the emmetropic eye, caused by non-parallel rays entering in the patient's eye.

FIG. 11. Distortion of the map of aberration refraction in the emmetropic eye, caused by non-parallel rays entering in the patient's eye.

FIG. 12. Rays placement of zero, first and second orders of diffraction in the direction of the axis X in the plane of aperture diaphragm of transferring telescope having slot variant of aperture diaphragm.

FIG. 13. Rays placement of zero, first and second orders of diffraction in the direction of the axis Y in the plane of aperture diaphragm of telescopic system of the selector.

FIG. 14. Design of aperture diaphragm with light catcher for parasitic scattering.

Let us investigate in details the implementation of the proposed device for measuring the aberration refraction of the eye, illustrated in the functional scheme in FIG. 1. Main components are a probing channel 1, a measuring channel 2 and a channel of positioning 3. Probing channel 1 is isolated from channels 2 and 3 by means of polarization beam splitter 4, and radiation, exiting from the eye, is divided between channels 2 and 6 by the first beam splitter 5.

Acousto-optic crystals 7 and 8 of correspondingly the first and the second single- coordinate diffraction deflectors are placed in the probing channel 1 at the exit of the light source 6 . Transferring telescope of the equivalent center of rays deflection by the first deflector in the equivalent center of rays deflection by the second deflector is placed between crystals 7 and 8. Transferring telescope is designed in accordance with a Kepplerian scheme, and it includes the entrance lens 9 and the exit lens 10. The aperture diaphragm 11 is set in the point, where the back focus of the entrance lens 9 coincidences with the front focus of the exit lens 10. Transferring telescope is placed in a such way, that its entrance pupil coincidences with the equivalent center of rays deflection by the first deflector, and its exit pupil coincidences with the equivalent center of rays deflection by the second deflector. Laser, which irradiates in the next infrared area of the spectrum, is usually used as the light source. It is also possible to use a laser, which irradiates in the visible range. It is advisable to use a semiconductor laser, however, the type of laser is not a limitation.

Selector of the first order of diffraction is set at the exit of the crystal 8 of the second deflector. It is designed in accordance with a Kepplerian scheme with the entrance lens 12, the exit lens 13 and the aperture diaphragm 14, which is placed in the point of foci coincidence of the entrance and the exit lenses. Selector is set in a such way that its entrance pupil coincidences with the equivalent center of rays deflection by the second deflector.

Polarization beam splitter 4 is placed after the selector. Laser radiation is directed into the patient's eye 16, whose main elements of an optical system include cornea 17, lens 18 and retina 19. Polarization beam splitter 4 reflects one polarization (perpendicular to the plane of the drawing) in the direction of the eye, and allows the other one to pass through, this one being orthogonal, is contained in the exiting from the eye 16 due to depolarization of the radiation in the process of light scattering on the retina 19.

Objective lens 20, in whose focal plane position-sensitive photodetector 21 is placed, is located at the eye exit of the eye after polarization beam splitter 4 and the first beam splitter 6. The position-sensitive photodetector may be the matrix of charged-coupled devices (CCD) of television type, quadrant photodetector, multielement array of photodetectors, single- or two-coordinate position-sensitive elemental receivers. CCD matrix has some advantages in information interpretation and processing, but its main disadvantage is slow information transfer. In the matrixes for standard television the full measurement cycle of in one eye takes 4 seconds for 100 entrance points, that is too long to avoid eye movements during measurement. Quadrant receiver has significant advantages in high-speed and information processing, but it may be used only in the restricted range of measured refraction errors (2-3 dioptres) due to non-linearity of discriminatory characteristic. Providing wide range of measured values (10-15 dioptres) maximum accuracy can be achieved using multielement arrays. Their disadvantage is comparative high price (3000 grivnias for 512 elements) and more complicated information processing. Satisfactory results ensuring low price may be achieved using single-coordinate, and better two-coordinate position-sensitive elemental receivers. Information processing in this case is as easy as for the quadrant receiver, and the total price is only 100-200 grivnias.

The exit of the position-sensitive photodetector 21 is linked to the computer 22, which is the part the unit for information processing and display 23. Converting the input signals and producing the signals for the interaction of all components of the device as a whole is realized by means of the special electronic schemas, which is the part of the unit for information processing and display 23 (not indicated in the drawing). It is more convenient to place them in the computer case. Measurement channel consists of objective lens 20, position-sensitive photodetector 21 and unit for information processing and display 23 on basis of computer 22.

To computer 22 is linked digital frequency synthesizer 24, to whose output connected output amplifier-driver 25, outputs of which are connected to launching coils of acousto- optical crystals 7 and 8 of correspondingly the first and the second single-coordinate deflectors.

Several infrared (IR) light emitting diodes (LEDs) 26 are set in front of patient's eye (two of them 26' and 26" being shown in the drawing). There can be four, six or another number of LEDs.

A first beam splitter 5 is set along the path of radiation exiting from the eye, and the second beam splitter 27 is placed after the first on the path of light reflected back by it. Along the way of radiation, passed through the beam splitter 27, the following components are installed: an objective lens 28, a television CCD matrix 29 sensitive up to infrared radiation. A TV signal former 30 is connected to the output of the matrix 29 and linked to the computer 22.

In front of the reflecting surface of the beam splitter 27 (starting from the farthest component) there are successively installed: a visible light emitting diode 31, a transparent plate 32 with deposited collimating cross-hairs, and an optical system for driving patient's eye accommodation (Badal optometer), which is composed of a pancratic group of lenses 33, 34. At least one of the lenses is made movable. Components 27-34 are parts of the channel 3 of positioning, orientation and providing an accommodation state.

Laser 8 - through the link a, light emitting diodes 33 - through the link b, light emitting diode 40 - through the link c, and electric driver 46 - through the link d are linked to the computer 29.

Laser 6 through connection a, LED's 26 through connection b, LED 31 through connection c are connected to computer 22.

The above described device operates in the following manner. In correspondence with the existing practice and recommendations of the Working Group of the subcommittee of the Optical Society of America (A. Bradley, et al. Reference axis selection: A subcommittee report of the OS A working group to establish standards for the measurement and reporting of the optical aberration of the eye. In: Vision Science and Applications. Optical Society of America, Technical Digest, 2000, pp. 148-150), patient's eye is positioned and oriented at first in such a way, that its line of sight coincides with the optical axis of the device. For this purpose, patient has to direct his sight to the center of the collimating crosshairs 32, which are illuminated by the light emitting diode 31. Then, the device is positioned relatively to the patient's eye so that the axis of the device passes through the center of curvature of the cornea. Correct mutual positioning and orientation of the eye and the device is indicated by a symmetrical disposition of reflexes of the light emitting diodes 26 on the screen of the monitor 22. This pattern is visualized using the television CCD matrix 29, the TV signal former 30, and an input-output interface (framegrabber, frame catcher) that is included in the unit for information processing and display 23 or the computer 22.

When the apex of the cornea is crossed by the optical axis of the device and when the line of sight of the eye coincides with the optical axis of the device, the surface of the cornea 17, as a convex mirror, forms visible images of light emitting diodes 26 positioned symmetrically with regard to the axis of symmetry of the surface. Their secondary image in the working image plane of the objective lens 26 will be also symmetrical with regard to the optical axis of the device.

Directly before the measurements, patient has to make the eye to accommodate to a certain distance set by means of the optical system 33-34. The major part of the accommodation is performed by the lens 18. Most frequently, measurements are performed with the relaxed accommodation of the lens. For this purpose, one of the lenses 33 or 34, is moved until it reaches a position corresponding to the position of the collimating cross-hairs 32 at infinity. For better relaxation, it is even possible to "increase" this distance (by continuing to move the lens or, by means of instantaneous introduction of an additional lens).

After these operations, in which a significant part is taken by an operator, the further control of the processes of measurement is performed by the computer. First, the laser 6 is turned on. From the exit of laser 6 the light beam is successively directed in acousto-optic crystal 7 of the first deflector, and then - to acousto-optic crystal 8 of second deflector through transferring telescope of equivalent center of deflection 9-10 with aperture diaphragm 11. As a result the both deflection centers (on the axis X and axis Y) coincide. Crystals 7 and 8 control the driver 25, which is amplifier of control signals, generated by the digital frequency synthesizer 24, which in turn are set by computer 22.

By means of telescopic system of selector 12-13 the mutual deflection center is replaced from the crystal 8 to the entrance pupil of the telescopic system 12-13 (back focus of the lens 13), which coincidences with front focus of collimating lens 15. Lens 15 converts narrow parallel beam, exiting from the deflection center F₁₅-F₁₃', in light beam parallel to the optical axis, which directed in the patient's eye by means of polarization beam splitter 4 . The points for an eye entering are selected in order to fill entire entrance aberture of the eye during given measurement procedure. Typically the total number of the points during the successively (in time) procedure of laser beam entering is 60-100, but may be even more.

The time of beam being in one point is controlled by a program, typically it takes 0,1- 0,2 milliseconds. Thus, total time of one measurement procedure is 6-20 milliseconds.

Radiation scattered by the retina, which exited from the eye, after passing through the light beam splitter 5 is projected on photosensitive plane of position-sensitive photodetector 21 by means of objective lens 20. Measured by photodetector value of deflection of projected on the eye beam from axial position is stored into computer's memory with coordinates of beam entering point in the eye. Having these data for all points of the eye entrance, one can find an analytic form of phase front surface, as a rule, approximated using Zernike polynomials. Aberrations for all points of the entrance aperture are calculated on base of these data. The example of the map of phase front is illustrated in FIG. 2, where colour spectrum corresponds to different front deflections from flat (in micrometers). The example of aberration map is depicted in FIG. 3. In this map colour spectrum indicates different local deflections of optical power of the eye (in dioptres) from the value, which corresponds to the emmetropic eye.

To prove the advantages of proposed technical solution over the next analogue we will examine in detail the course of rays in the probing channel 1. Beam deflection in the direction of the coordinate X, caused by the crystal 7 of the first deflector, is depicted in FIG. 4 . We will use in FIG. 4 and hereinafter the same elements indications, as shown in FIG. 1. In addition, F will mean the front focuses, and F' - the back focuses of lenses, here the subscript corresponds to lens, to which the indicated point relates.

As described in work of Kolenov (Candidate dissertation. Kiev National University, Radiophysical Department, 2001), for diffraction scanning is typical some virtual (we will name it hereinafter equivalent) scanning center (deflection), which does not change its position by different angles of deflection. For simplification we will consider, that this center coincides with geometric center of crystal. For the same purpose of simplification (that does not influence on generalization of conclusions) we will not depict in drawings the changes of ray course, which are caused by difference of index of refraction in the air and in crystal. This means that specialist in optics are familiar with these questions. Additionally the crystal will be illustrated in the form of a cube. Thus, Oj - equivalent center of beams deflection in the first crystal 7 in the direction X; Oi' -center of beams deflection in the direction X, replaced in center of the crystal 8 of the second deflector. O₂ - equivalent center of beams deflection in the second crystal 8 in the direction of the axis Y.

Parallel beam from the exit of the laser 6 is directed it the crystal 7, where it is deflected in the direction of the axis X. Transferring telescope 9-10 replaces image of deflection center O] in the first crystal in Oi' point, that coincides with deflection center O in the direction of the axis Y in crystal 8 of the second deflector. Telescopic system 12-13 replaces the scanning center from the point O₂ in the point (Oi" - O₂"), where the back focus of the lens 13 coincides with the front focus of collimating lens 15. After the lens 15 the beam is directed in the eye in parallel to the optical axis of device. If the eye is emmetropic, this beam will be projected on the retina with zero deflection from the axis.

The process of deflection in the direction of the axis Y is similar, but this deflection occurs in the crystal 8. This deflection is depicted in FIG. 5: the plane of this image oriented at 90° angle relative to plane in FIG. 4 (in other words, FIG. 5 is side view of FIG. 4). In this case the deflection center O is replaced by telescopic system 12-13 in the same point (Oi" - O "), where the back focus of the lens 13 coincides with the front focus of collimating lens 15. As in above mentioned case, the beam directs in the eye in parallel to the optical axis of device after the lens 15. If the eye is emmetropic, it will be projected on the retina with zero deflection and in direction of axis Y. It means that the result of measurement will be without the errors.

To compare the advantages of the proposed technical solution over the technical solution of the next analogue let us examine the case, when the deflection centers in orthogonal directions do not coincide with each other and/or with the front focus of the collimating lens. According to the technical solution of the next analogue the both crystals are placed side-by-side without transferring telescope between them, and the entrance pupil of selector is positioned in the gap between these crystals. Then, as depicted in FIG. 6, in scanning plane in the direction of the axis X the deflection center will be replaced by selector in the point Oi", which is located ahead the point of the front focus F15 of the collimating lens 15 (that coincides with the back focus F₁₃' of the lens 13). As the result (FIG. 7) the beam, deflected in the direction of the axis X, will intersect the cornea in the point C_x, and the retina in the point R_x at some distance δχ, which by refraction calculation will cause the error in the myopia direction. Similarly while analyzing deflections in the direction of the axis Y we will notice (FIG. 8), that the deflection center will be replaced by selector in the point O ", which is located behind the point of the front focus F₁₅ of the collimating lens 15 (which under the same condition coincides with the back focus F₁₃' of the lens 13). As a result (FIG. 9) the beam deflected in the direction of the axis Y will intersect the cornea in the point C_y, and the retina in the point R_y at some distance δχ, that by refraction will cause the error in the hypermetropia direction.

Such type of errors is illustrated in FIG. 10 for the wave front and in FIG. 11 for the refraction distribution. As depicted in these drawings, the horizontal axis X is myopic, and the vertical (y) - hypermetropic. As can be seen, the error by ametropy calculation reaches ± 1 dioptres, that is insufficient for accurate measurements.

This error correction in the technical solution of the next analogue becomes more complicated due to undetermined position of the entrance pupil of the telescopic system of selector in the gap between crystals. Due to adding in the proposed technical solution the transferring telescope of the equivalent center of beams deflection by the first deflector in the equivalent center of beam deflection by the second deflector, conditions for exclusion of undetermined position of the front focus of collimating lens are created - it coincides with the exit pupil of the telescopic system of selector and corresponds to coincided center of beams deflection in both directions. In the result the error by measuring of aberration refraction of optical system of the eye, caused by undetermined position of the collimating lens, was excluded.

Furthermore, adding the transferring telescope of the equivalent center deflection ensures the additional suppression of zero and higher orders of diffraction. This task is solved, by designing the transferring telescope as a Kepplerian scheme, which comprises lenses 9 and 10, and adding in it aperture diaphragm 11 (FIG. 1, 4, 5), positioned in the point of foci coincidence of the entrance and the exit lenses of transferring telescope. Here the aperture diaphragm performs the function of radiation selector in the first order of diffraction in the direction of the axis X, in such way excluding the major part of radiation from the further scattering.

In addition, the effectiveness in suppression of zero and higher orders of diffraction is reached by means of designing aperture diaphragm of transferring telescope in the form of a slot, whose longer side is oriented along the direction of the beams deflection by the first deflector (FIG. 12). Slot configuration of the aperture diaphragm instead of the circular reduces the area, through which parasitic diffraction side lobes may pierce the exit of deflector. In this case aperture diaphragm, placed in the telescopic system of selector, will be reached by radiation originated only from the first order of diffraction in the direction of the axis X (FIG. 13). Slot width has to correspond to width of in-focus laser beam, and its length to range of angular deflections. In practice manufacturing and implementation tolerance has to be taken into account. In one of the invention implementation sizes of such diaphragm take 0,2x1,2 mm.

Furthermore, as a variant of the transferring telescope implementation, the cylindrical lenses may be used in it instead of the spherical, which have to be places in such way, that their meridian axis will be oriented along the direction of beams deflection by the first deflector, it means along of the axis X. This technical solution is equivalent to the solution with spherical lenses.

In addition, the effectiveness in suppression of zero and higher orders of diffraction, which are not used for scanning, can be increased in present invention in such way, that light catchers (FIG. 14) are placed in the transferring telescope (which comprises lenses 9 and 10) and in the selector of first order of diffraction (which comprises lenses 12 and 13) around the aperture diaphragm 11 or/and 14 outside the zone of the first order of diffraction in both directions of light beams deflection. In the particular technical solution illustrated in FIG. 14 the light catcher is designed in the form of two conic surfaces, which impinge at right angle. These surfaces have light-absorbing coating. Light catchers have not only the conic form of the surfaces. But it is important that the maximum of indicatrix of diffusion of the light scattered by such surfaces is toward to the opposite surface of the catcher.

In such way the double suppression of the scattered parasitic radiation, corresponding to zero and higher orders of diffraction, is achieved in the invention by adding of the aperture diaphragm in the transferring telescope, which in one of the variants contains the cylindrical lenses, by designing aperture diaphragm in form of a slot and adding of the light captures for radiation of zero and higher orders of diffraction.

Claims

1. A device for measuring the aberation refraction of the eye, which contains a probing channel, a measuring channel and a channel of positioning, orientation and providing an accommodation state of the eye, whereas the probing channel is being composed of a laser, two single-coordinate deflectors, selector the first order of diffraction and collimating lens, which are arranged in series, whereas the selector of the first order of diffraction is designed in accordance with a Kepplerian scheme as a telescope with aperture diaphragm, set at the point of foci coincidence of entrance and exit lenses, the point of the front focus of collimating lens is located in the plane of the exit pupil of the telescope, each single- coordinate deflector includes a acousto-optic crystal, controled by a digital frequency synthesizer through output amplifier-driver, polarization beam splitter, whose orthogonal exit is directed to the measuring channel, is set after collimation lens in the front of patient's eye, measuring channel includes a objective lens, which is placed in its focal plane of the position- sensitive photodetector, whose output is linked to a unit for information processing and display on the basis of a computer, which, performing controlling functions, connected to a laser, deflectors and a channel of positioning, orientation and providing an accommodation state of the eye, c h a r a c t e r i z e d in that the transfering telescope of equivalent center of beams deflection by the first deflector into the equivalent center of beams deflection by the second deflector is placed between acousto-optic crystals of single-coordinate deflectors in a such way, that the entrance pupil of transferring telescope coincides with equivalent center of beams deflection by acousto-optic crystals of the first deflector, and the exit pupil of transferring telescope and the entrance pupil of selector of the first order of diffraction coinciedes with equivalent center of beams deflection by acousto-optic crystals of the second deflector.

2. A device according to Claim 1, wherein the device is c h a r a c t e r i z e d in that the transfering telescope is designed in accordance with a Kepplerian scheme and with addition of aperture diaphragm, set at the point of foci coincidence of entrance and exit lenses of transfering telescope.

3. A device according to Claim 2, wherein the device is c h a r a c t e r i z e d in that the aperture diaphragm of transfering telescope is designed in the form of a slot, whose longer side is oriented along the direction of beams deflection by the first deflector.

4. A device according to Claim 3, wherein the device is characterized in that the transfering telescope is constructed from cylindrical lenses, whose meridian axis is oriented along the direction of beams deflection by the first deflector.

5. A device according to Claim 3, wherein the device is characterized in that the light catchers, for example in the form of light-absorbing coating, which impinge at right angle, are installed in transferring telescope and in selector of the first order of diffraction around of aperture outside the zone of the first order of diffraction of both light beams directions.

6. A device according to Claim 4, wherein the device is characterized in that the light catchers, for example in the form of light-absorbing coating, which impinge at right angle, are installed in transferring telescope and in selector of the first order of diffraction around of aperture outside the zone of the first order of diffraction of both light beams directions.