CN109674441B - Multi-beam elasticity measurement system and method based on optical switch and micro-lens array - Google Patents
Multi-beam elasticity measurement system and method based on optical switch and micro-lens array Download PDFInfo
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Abstract
The invention provides a multi-detection-beam optical coherence elasticity measurement system and an elasticity measurement method based on optical switch control and a micro-lens array. The measurement position of the cornea is positioned by adopting a cornea positioning subsystem, the cornea generates micro mechanical waves and deformation by adopting a cornea excitation subsystem, and the elastic reaction of each measurement point of the cornea is detected by adopting a multi-beam OCT detection subsystem. The multi-beam OCT detection subsystem adopts an elasticity measurement scheme based on rapid optical switch control and a micro-lens array, greatly improves the measurement speed, simplifies the system structure, reduces the manufacturing cost and can rapidly measure the elastic response of multiple directions and multiple positions around a sample (cornea) under single load excitation while ensuring the elasticity measurement performance of the system.
Description
Technical Field
The invention relates to the field of biomedical elastography, in particular to a multi-beam optical coherence in-vivo corneal elasticity measurement system and a multi-beam optical coherence in-vivo corneal elasticity measurement method based on ultrafast optical switch control and a micro-lens array.
Background
The cornea of the human eye is the main refractive medium of the human eye, and the elastomechanical characteristics of the cornea play an important role in maintaining the normal structure and function of the cornea and are an important basis for researching the physiological and pathological characteristics of the cornea. Corneal diseases (e.g., keratoconus, corneal ectasia) and corneal surgery (corneal refractive surgery, uv cross-linking CXL, etc.) cause changes in corneal elastomechanical characteristics. Conventional clinical testing methods diagnose based on corneal morphology (topography, thickness, curvature, etc.) and intraocular pressure parameters; although the detection rate of corneal diseases has been high, some corneal diseases are missed. And the small change of the corneal structure can cause the obvious change of the elastomechanics characteristic, so that the quantitative research aiming at the corneal elastomechanics characteristic has important significance on the diagnosis and treatment of corneal diseases. In order to realize the quantification of corneal elastomechanics characteristics in clinic, the development of a non-contact in-vivo human eye corneal elastography measurement technology has become a great demand and hot spot for ophthalmologic and visual science research.
At present, various cornea elasticity measuring techniques are still not mature, and the measured cornea mechanical parameters are different by several orders of magnitude. Taking Young's modulus measurements of rabbit corneas as an example, the estimates range from about 1kPa (Thomasy et. acta Biomate 10(2), 785. sup. 791(2014)) to about 11MPa (Wollensak et. acta Ophthalmol 87(1),48-51 (2009)). Ruberti et al propose several unsolved problems (Open questions) faced by corneal elastography measurement techniques, the first three of which are: "how to develop new techniques/instruments for measurement of elasticity in the body cornea", "how to distinguish the elasto-mechanical characteristics in various regions of the body cornea" and "how to perform pre-operative risk assessment of corneal surgery by means of elastography measurement" (Ruberti etc. annu Rev Biomed Eng 13,269-295 (2011)). In the in-vivo elasticity measurement scheme of the cornea, various elastography techniques have technical bottlenecks: or the high measurement resolution requirement (Voorhees etc. Experimental Eye Research,160,85-95(2017)) cannot be achieved, or the local measurement for the corneal lesion region (Luce etc. J Cataract Refract Surg31(1),156 and 162 (2005); Hong etc. IOVS54(1),659 and 665(2013)) cannot be achieved, or the excessive measurement time (Scarcell etc. Nat Photonics 2(1),39-43 (2008); Scarcell etc. IOVS 53(1),185 and 190(2012)) is required, so that the clinical requirement of the corneal in-vivo elasticity measurement is difficult to achieve. An important scientific problem faced by the present quantitative research on corneal elastic parameters is: how to quantify the elastomechanics characteristic of the cornea of human eyes more accurately, especially how to measure the elasticity parameter of the local area of the cornea with high precision and realize the boundary distinction between the pathological change or the operation area of the cornea and the normal area clinically. It is necessary to develop a new method for measuring corneal elasticity meeting clinical requirements and to develop a high-precision and rapid measurement technique capable of realizing the quantification of elastic parameters in a local area of the cornea and in multiple directions of the human eye.
In the OCE technology, it is difficult to realize the tracking of mechanical wave propagation of human cornea and the accurate in-vivo measurement of Young modulus by adopting the scanning detection type OCE at present. The mechanical wave propagation velocity is in the order of a few meters per second, and each measurement point requires several milliseconds to tens of milliseconds to obtain a "displacement-time" curve for that point. OCE is difficult to track mechanical waves in a certain propagation direction by single frame imaging. In addition, the measurement of the mechanical wave propagation velocity of the living cornea by the eye movements introduces a large measurement error. The traditional SD-OCT system adopts a method of multiple excitation and multiple detection to splice the elastic response of each measuring point of a sample and an isolated cornea, thereby realizing the estimation of the propagation speed of mechanical waves. However, due to the presence of eye movements, this method is difficult to use for elasticity measurement of the cornea in a human eye. High speed swept source OCT systems can increase the acquisition speed, for example 150 million A-lines/sec (Song etc. applied Physics Letters 108(19) (2016); Singh etc. Opt. Lett.40(11), 2588-. However, swept OCT still has a large phase error, and an additional phase stabilization technique is required to obtain a stable phase. In addition, high-speed frequency-sweeping OCT is expensive and difficult to popularize clinically. The Line field (Line field) scan OCE scheme (Liu et c. biological Optics Express 7(8),3021-3031 (2016)) can improve the detection speed of mechanical waves, but has not been successfully applied to the measurement of human cornea because it needs stronger light intensity signal.
In addition, some schemes such as (1) high-speed sweep oct (swept source oct) system can increase the acquisition speed, for example, 150 ten thousand a-lines/second (Song etc. applied Physics Letters 108(19) (2016); Singh etc. opt. lett.40(11),2588 + 2591 (2015)). However, swept OCT still has a large phase error, and an additional phase stabilization technique is required to obtain a stable phase. In addition, high-speed frequency-sweeping OCT is expensive and difficult to popularize clinically.
(2) While the OCE scheme (Liu et c. biological Optics Express 7(8),3021-3031 (2016)) using Line field scanning can improve the detection speed of mechanical waves, it has not been successfully applied to the measurement of human cornea because it requires a stronger light intensity signal.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is as follows: provides a micro-lens array multi-beam optical coherence in-vivo cornea elasticity measuring system controlled by an ultra-fast optical switch and a measuring method. The invention simplifies the structure, greatly reduces the manufacturing cost and simultaneously realizes the rapid, simultaneous and accurate in-vivo measurement of multiple elasticity parameters (hardness, natural frequency and Young modulus) of the cornea measurement position of the human eye.
The invention is realized by the following technical scheme: in one aspect, a multi-beam optical elasticity measurement system based on an optical switch and a microlens array is provided, which includes a multi-beam OCT detection subsystem and a load excitation subsystem, wherein the multi-beam OCT detection subsystem includes a broad spectrum light source, a fiber coupler, an optical switch, a sample arm, a reference arm and a spectral detector, the broad spectrum light source is connected to an input end of the fiber coupler, light emitted by the broad spectrum light source is split by the fiber coupler, one path is led to the reference arm, the other path is controlled by the optical switch to be led to the sample arm, interference spectra of light returning from the reference arm and the sample arm are received by the spectral detector after passing through the fiber coupler, each light path of the sample arm is provided with a collimator lens and a cylindrical lens which are matched with each other, a microlens array is further arranged at a position of each light path in front of a cornea, and the load excitation subsystem is used for exciting the cornea to generate micro mechanical waves and deform the cornea so as to facilitate the multi The OCT detection subsystem detects.
Further, the multi-beam optical elasticity measurement system based on the optical switch and the micro lens array further comprises a cornea positioning subsystem, wherein the cornea positioning subsystem is used for positioning the position of the cornea to be measured, the cornea positioning subsystem comprises a positioning camera, dynamic displacement of the cornea along the axial direction of the coherent measurement system is tracked by an OCT (optical coherence tomography), and dynamic displacement of the cornea along the transverse direction of the coherent measurement system is tracked and positioned by the positioning camera.
Further, the microlens array includes microlens units having different focal lengths in various directions and different optical path differences.
Further, the sample arm measures not less than 4 positions around the cornea excitation point, and the number of measurement points in each position is not less than 2.
Furthermore, the optical switch is a super-fast optical switch, the on/off switching time of the super-on-speed optical switch is not more than 1ms, and the alternating and repeated acquisition of each direction in sequence is realized.
On the other hand, the multi-beam optical elasticity measuring method based on the optical switch and the microlens array, which uses the multi-beam optical elasticity measuring system based on the optical switch and the microlens array in the above technical solution, includes the steps of:
s1, imaging the cornea and the pupil of the eye by using a positioning camera, transversely positioning the cornea according to the edge and the central point of the pupil, axially tracking through the depth change of a mark point on an A-scan in an OCT signal, exciting the surface of the cornea through a load excitation subsystem when the axial position and the transverse position of the cornea are within the measurement error range, detecting the generated mechanical wave and the micro deformation of the cornea through an OCT detection subsystem, and evaluating the elastic characteristic of the cornea.
S2, in the OCT detection subsystem, the light emitted by the broad spectrum light source is transmitted into the optical fiber coupler through the optical fiber, after the measurement light is split in the optical fiber coupler, one end of the measurement light is led to the reference arm, and the other end of the measurement light is led to the ultrafast optical switch, wherein the ultrafast optical switch controls a multidirectional detection light path; each detection light path corresponds to a measurement direction, after the light of each detection light path is subjected to the combined action of the collimating lens and the cylindrical lens, the light beam of each detection light path is expanded into a strip-shaped light spot, and the light spot is respectively irradiated on the corresponding position of the micro lens array in front of the cornea, is divided into a plurality of measurement points by the micro lens array and is focused on the cornea; each path of detection light is alternately and repeatedly collected around the corneal excitation point in sequence in multiple directions under the control of the ultrafast optical switch; and the reference arms and the corresponding sample arms interfere with each other in pairs and are detected by the spectral detectors corresponding to the spectral detector group.
Further, an image intensity signal and a time-varying phase signal of each measurement point are acquired, and the surface deformation information of the measurement point can be obtained by calculating the phase signal of each measurement point.
Further, a recovery curve of the measured cornea is obtained, and the natural frequency of the cornea is obtained by fitting the recovery curve to an exponential decay curve.
Further, the stimulated damping vibration information of the cornea is obtained, and fast Fourier transform is carried out to obtain the natural frequency of the cornea.
Further, deformation information and time delay information of each measurement point are acquired, and the Young modulus is calculated according to a mechanical wave propagation model.
The invention provides a multi-beam optical elasticity measurement system and a method based on an optical switch and a micro-lens array, wherein the optical switch is used as a key control element to control a plurality of detection light paths in different measurement directions, the system has a simple structure, can quickly measure elastic responses of a plurality of measurement positions of human cornea excitation points under single excitation without galvanometer scanning, and realizes quick and accurate in-vivo measurement of a plurality of elastic parameters (hardness, inherent frequency and Young modulus) of the human cornea measurement positions.
Drawings
FIG. 1 is a schematic diagram of a multi-beam optical elastometry system based on an optical switch and a microlens array;
FIG. 2 is a schematic structural diagram of a microlens array;
FIG. 3 is a schematic cross-sectional structure of a microlens array;
FIG. 4 is a schematic diagram of the structure of a sample arm;
FIG. 5 is a schematic view of the location of the excitation point and the measurement point on the cornea;
FIG. 6 is a graph of the signals acquired for each measurement point, (a) is a graph of the intensity at each measurement point; (b) the phase map for each measurement point.
FIG. 7 is a diagram of the spectrum detector collecting the interference superimposed signals of multiple points in four directions of the cornea alternately and repeatedly in sequence;
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
As shown in fig. 1, 2, 3, 4 and 5, the present embodiment provides a multi-beam elasticity measurement system based on an optical switch and a microlens array, which includes an OCT detection subsystem and a load excitation subsystem 2, the OCT detection subsystem includes a broad spectrum light source 11, a fiber coupler 12, an optical switch 13, a sample arm 14, a reference arm 15 and a spectrum detector 16, the broad spectrum light source 11 is connected to an input end of the fiber coupler 12, light emitted from the broad spectrum light source 11 is split by the fiber coupler 12 and led to the reference arm 15, another light led to the sample arm 14 is controlled by the optical switch 13, interference spectra of light returning from the reference arm 15 and the sample arm 14 are received by the spectrum detector 16 after passing through the fiber coupler 12, each light path of the sample arm 14 is provided with a collimating mirror 141 and a cylindrical mirror 142 which are matched with each other, each optical path is also provided with a micro lens array 143 in front of the cornea 61, and the load excitation subsystem 2 is used for exciting the cornea 61 to generate micro mechanical waves and deformation to the cornea 61 so as to facilitate detection by the OCT detection subsystem. For convenience of description, the light path on the reference arm 15 is defined as a reference light path, and the light path on the sample arm 14 is defined as a detection light path.
The optical switch 13 of this embodiment adopts an ultrafast optical switch, the on/off switching time of which is not more than 1ms, the speed of the ultrafast optical switch adopted in this embodiment is 50ns, referring to fig. 7, the ultrafast optical switch is switched in each direction, and the elastic response of multiple measurement positions around the cornea excitation point of the human eye under single load excitation can be rapidly measured without galvanometer scanning under the condition that only one reference arm 15 and one spectrum detector 16 are needed for controlling the multiple detection optical paths to alternately and repeatedly collect multiple directions around the cornea excitation point in sequence, so that high-precision and rapid in-vivo measurement of multiple elastic parameters (hardness, natural frequency and Young modulus) in the local area of the cornea of the human eye and elastic parameter distribution (anisotropy) in each area of the cornea 61 is realized.
The multi-detection-beam optical coherence measurement system based on the microlens array further comprises a cornea positioning subsystem, wherein the cornea positioning subsystem is used for positioning the position of a cornea to be measured, the cornea positioning subsystem comprises a positioning camera 31, dynamic displacement of the cornea along the axial direction of the coherence measurement system is tracked by OCT, and dynamic displacement of the cornea along the transverse direction of the coherence measurement system is tracked and positioned by the positioning camera.
The positioning camera 31 is focused on the pupil. In view of the fact that the lateral eye movement affects the accuracy of the measurement position of the cornea, the positioning camera 31 is adopted to image the pupil of the human eye, and the cornea is transversely positioned according to the edge and the central point of the pupil, so that the measurement position error caused by the lateral eye movement is reduced.
The microlens array 143 includes microlens units 1431 having different focal lengths in various directions and different optical path differences. By adopting the micro-array lens as a key optical element, the multi-direction and multi-position elastic response around the excitation point of the sample (human eye cornea) under single load excitation can be simultaneously measured without adopting a mode of galvanometer scanning as in the traditional OCE and rotating the sample arm, so that the high-precision and quick in-vivo measurement of the multi-elasticity parameters (hardness, inherent frequency and Young modulus) of the local area of the human eye cornea and the elastic parameter distribution (anisotropy) of each area of the cornea is realized.
The load excitation subsystem 2 is a device suitable for human cornea excitation. The load excitation subsystem 2 may be a device suitable for corneal excitation of the human eye that should be non-toxic, non-harmful, and safe to the eye, particularly corneal tissue. In the embodiment, a trace gas pulse device is adopted, and when the trace gas pulse device is used, trace gas is sprayed out of a target to be detected, so that the target to be detected forms instantaneous pressure change, and the target to be detected generates mechanical waves.
The sample arm 14 measures not less than 4 orientations around the excitation point O of the cornea 61, and the number of measurement points in each orientation is not less than 2. The present embodiment employs detection of four orientations. Respectively azimuth 1, azimuth 2, azimuth 3 and azimuth 4, and for convenience of description, only the optical paths of the sample arm 14 for azimuth 1 and azimuth 3 are shown in fig. 1. In the same azimuth, there are 4 measurement points, taking azimuth 1 as an example, measurement point a, measurement point B, measurement point C, and measurement point D.
The initial positions of the measurements were: the corneal vertex is used as an excitation point O to detect the Superior (Superior direction), Inferior (Superior direction), Temporal (Temporal direction) and Nasal (Nasal direction) of the cornea. Each direction of the four-directional microlens array 143 has a plurality of microlens units 1431 having different focal lengths (the focal length ranges from 3mm to 10mm in the present embodiment) and different optical path differences, and samples an area of the cornea 61 laterally distant from 3mm to 4mm in that direction. The focal length of each lens is designed for a model of a human cornea, so that each light beam is more effectively focused on each measurement point of the cornea 61. And each lens design introduces a characteristic optical path, so that signals of each measuring point can be distinguished conveniently.
Correspondingly, by using the above device, the present embodiment further provides an elasticity measuring method, including the steps of:
s1, imaging the cornea and the pupil of the eye by using the positioning camera 31, transversely positioning the cornea 61 according to the edge and the central point of the pupil, axially tracking the depth change of a mark point on an A-scan in an OCT signal, starting to excite the surface of the cornea 61 by the load excitation subsystem 2 when the axial position and the transverse position of the cornea 61 are within the measurement error range, detecting the generated mechanical wave and the micro deformation of the cornea 61 by the OCT detection subsystem, and evaluating the elastic characteristic of the cornea 61;
s2, in the OCT detection subsystem, the light emitted by the broad spectrum light source 11 is transmitted into the optical fiber coupler 12 through the optical fiber, after the measurement light is split in the optical fiber coupler 12, one end of the measurement light is transmitted to the reference arm 15, and the other end of the measurement light is transmitted to the ultrafast optical switch 13, and the ultrafast optical switch 13 controls the multi-directional detection light path; each detection light path corresponds to a measurement direction, after the light of each detection light path passes through the combined action of the collimating lens 141 and the cylindrical lens 142, the light beam of each detection light path is expanded into a strip-shaped light spot (refer to fig. 2), and the light beam irradiates the corresponding position of the micro lens array 143 in front of the cornea 61 respectively, is divided into a plurality of measurement points by the micro lens array 143, and is focused on the cornea 61; under the control of the ultrafast optical switch 13, each path of detection light is alternately and repeatedly collected around the excitation point O of the cornea 61 in sequence in multiple directions; each path of reference arm 15 and the corresponding sample arm 14 interfere the returned light two by two, and are detected by the spectral detectors 16 corresponding to the spectral detector group.
After the information obtained by the spectral detector 16 is analyzed, the following can be obtained: the deformation amplitude of the phase signals of each measuring point changing along with the time is reduced gradually along with the increase of the distance, and each phase signal has time delay, and the surface deformation information is obtained through calculation:
wherein t isJAnd t0Is at a time node, t, of a series of A-scan signals0Is a reference time point, λ0Is the center wavelength, and the stiffness of the cornea can be estimated from the magnitude of the main deformation after the deformation information is calculated.
By combining the simulation diagrams for simultaneously acquiring the four measurement point signals given in fig. 6(a) and (b), the interference characteristics of each point signal can be determined according to the optical path difference characteristics (including the optical path difference characteristics introduced during designing the multiple light beams) between each measurement point and the reference surface, and the interference noise including the pseudo signal can be suppressed or filtered. The main deformation (curve in figure 6 (b)) magnitude is directly affected by the excitation load. Relatively stiff samples deform less under the same driving force; while the primary deformations of equal magnitude decay more rapidly in the relatively hard sample. The degree of softness or hardness of the sample (cornea) can thus be determined by the magnitude of the main deformation. The measurement scheme of the project for the main deformation amplitude is as follows: 1. the magnitude of the main deformation of the sample (cornea) at the measurement point #1 was measured at the same gas pulse pressure. 2. Under a certain excitation pressure range, the curve of the main deformation amplitude of the sample (cornea) at the measuring point #1 along with the change of the gas pulse pressure is measured. 3. The attenuation of the main deformation amplitude of each measurement point (e.g., measurement points a to D) with increasing propagation distance is measured. From which the hardness of the sample can be estimated.
After the information obtained by the spectral detector 16 is analyzed, the following can be obtained: measuring the recovery curve of the cornea 61 and achieving natural frequency measurement by fitting the recovery curve to an exponential decay curve; the natural frequency of the cornea 61 can also be obtained by high-resolution detection and Fast Fourier Transform (FFT) of the excited damped vibrations of the cornea 61.
Specifically, the method for measuring the natural frequency according to the recovery curve comprises the following steps: since the recovery curve (curve in fig. 6 (b)) is related to the viscoelasticity (viscoelasticity) of the sample, indirect measurement of the natural frequency can be achieved by fitting the recovery curve to an exponential decay curve according to a dynamic model described in Wu c.etc. iovs.2015,56(2): 1292-.
Where ξ is the attenuation coefficient (damming Ratio) and f is the natural frequency. The differential equation (2) for damping vibration can be solved according to three conditions, which are: critical-damping (ξ ═ 1), under-damping (0 ≦ ξ <1), and over-damping (ξ > 1).
Where the amplitude constants a and B are derived from an exponential fit of the recovery curve.
The method for measuring the natural frequency according to the damping vibration comprises the following steps: frequency resolution (f) of FFT0) The smallest frequency interval that can be resolved is indicated. Can be represented by the following formula:
wherein fs is the sampling frequency, tsIs the sampling time (i.e., temporal resolution), N is the number of sampling points, and T is the length of the sampling time. To improve the frequency resolution of the FFT, the data may be processed in two steps before the FFT as follows. 1. Zero padding (Zero padding): within the sampling time of OCT (e.g. 30ms), the damped vibration amplitude of the cornea will beGradually tending to zero. Therefore, the zero padding method can be adopted for the data, and the sampling time is extended. 2. Splicing: the common-path OCT has an ultra-stable phase, and the phase before and after the elastic sample is excited is basically kept unchanged. Therefore, the data (with zero padding) in the adjacent excitation periods can be subjected to period expansion through splicing, and the total sampling time and the number of sampling points are increased.
The method for calculating the Young modulus according to the propagation speed of the mechanical wave comprises the following steps: after the information obtained by the spectral detector 16 is analyzed, the following can be obtained: and (3) a mechanical wave propagation model, and calculating the Young modulus of the region through the mechanical wave propagation model:
wherein c isi,j＝(di-dj)/(ti-tj) I, j represent any two measurement points, diAnd djRepresenting the distance, t, between any two measurement points and the stimulated point along the corneal surfaceiAnd tjRepresenting the propagation time of the mechanical wave between any two measurement points, ci,jAnd represents the propagation speed of the wave between any two measurement points, wherein rho is density and nu is Poisson ratio.
The embodiments described above with reference to the drawings are only preferred embodiments of the present invention and do not set the scope of the present invention, and any modifications made based on the idea of the present invention should be construed as being within the scope of the present invention.
Claims (5)
1. The multi-beam optical elasticity measurement method based on the optical switch and the microlens array is characterized in that a multi-beam optical elasticity measurement system based on the optical switch and the microlens array is utilized, and the multi-beam optical elasticity measurement system based on the optical switch and the microlens array comprises the following components: a multi-beam OCT detection subsystem, a load excitation subsystem, the multi-beam OCT detection subsystem including a broad spectrum light source, a fiber coupler, a light switch, a sample arm, a reference arm, and a spectrum detector, the wide spectrum light source is connected with the input end of the optical fiber coupler, light emitted by the wide spectrum light source is split by the optical fiber coupler, one path of light is led to the reference arm, the other path of light is controlled by the optical switch to be led to the sample arm, light returned from the reference arm and the sample arm is received by the spectrum detector after passing through the optical fiber coupler, each light path of the sample arm is provided with a collimating lens and a cylindrical lens which are matched with each other, a micro-lens array is arranged at the position of each light path in front of the cornea, the load excitation subsystem is used for exciting the cornea to enable the cornea to generate micro mechanical waves and deformation so as to facilitate the detection of the multi-beam OCT detection subsystem;
the multi-beam optical elasticity measurement system based on the optical switch and the micro lens array further comprises a cornea positioning subsystem, wherein the cornea positioning subsystem is used for positioning the position of a cornea to be measured and comprises a positioning camera, the dynamic displacement of the cornea along the axial direction of the coherent measurement system is tracked by OCT, and the dynamic displacement of the cornea along the transverse direction of the coherent measurement system is tracked and positioned by the positioning camera; the micro lens array comprises micro lens units with different focal lengths in all directions and different optical path differences; the sample arm measures not less than 4 directions around the cornea excitation point, and the number of measurement points in each direction is not less than 2; the optical switch is a super-fast optical switch, the on/off switching time of the super-on-speed optical switch is not more than 1ms, and the alternating and repeated acquisition of each direction in sequence is realized;
further comprising the steps of:
s1, imaging the cornea and the pupil of the eye by using a positioning camera, transversely positioning the cornea according to the edge and the central point of the pupil, axially tracking through the depth change of a mark point on an A-scan in an OCT signal, exciting the surface of the cornea through a load excitation subsystem when the axial position and the transverse position of the cornea are within a measurement error range, detecting the generated mechanical wave and the micro deformation of the cornea through an OCT detection subsystem, and evaluating the elastic characteristic of the cornea;
s2, in the OCT detection subsystem, the light emitted by the broad spectrum light source is transmitted into the optical fiber coupler through the optical fiber, after the measurement light is split in the optical fiber coupler, one end of the measurement light is led to the reference arm, and the other end of the measurement light is led to the ultrafast optical switch, wherein the ultrafast optical switch controls a multidirectional detection light path; each detection light path corresponds to a measurement direction, after the light of each detection light path is subjected to the combined action of the collimating lens and the cylindrical lens, the light beam of each detection light path is expanded into a strip-shaped light spot, and the light spot is respectively irradiated on the corresponding position of the micro lens array in front of the cornea, is divided into a plurality of measurement points by the micro lens array and is focused on the cornea; each path of detection light is alternately and repeatedly collected around the corneal excitation point in sequence in multiple directions under the control of the ultrafast optical switch; each path of reference light and each path of detection light of the corresponding sample arm return and interfere with each other, and are detected by the spectral detectors corresponding to the spectral detector group;
simultaneously measuring the multi-directional, multi-positional elastic response around the excitation point of the cornea under a single load excitation.
2. The multi-beam optical elasticity measurement method based on the optical switch and the microlens array according to claim 1, wherein: and acquiring an image intensity signal and a time-varying phase signal of each measuring point, and calculating the phase signal of each measuring point to obtain the surface deformation information of the measuring point.
3. The multi-beam optical elasticity measurement method based on the optical switch and the microlens array according to claim 1, wherein: the recovery curve of the measured cornea is obtained and the natural frequency of the cornea is obtained by fitting the recovery curve to an exponential decay curve.
4. The multi-beam optical elasticity measurement method based on the optical switch and the microlens array according to claim 1, wherein: and acquiring the stimulated damping vibration information of the cornea, and performing fast Fourier transform to obtain the natural frequency of the cornea.
5. The multi-beam optical elasticity measurement method based on the optical switch and the microlens array according to claim 1, wherein: and acquiring deformation information and time delay information of each measuring point, and calculating the Young modulus according to a mechanical wave propagation model.
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