CN118078203B - Optical coherence tomography device for synchronously measuring cornea and retina of eye - Google Patents
Optical coherence tomography device for synchronously measuring cornea and retina of eye Download PDFInfo
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Abstract
The invention relates to an optical coherence tomography device for synchronously measuring cornea and retina of an eye, belongs to the technical field of optical imaging, and solves the problems that an OCT system is short in interference length and limited in imaging depth. The device comprises: a low coherence light source, a fiber coupler, a reference arm, a measurement arm, and a spectrometer; light emitted by the low-coherence light source is divided into two paths after passing through the optical fiber coupler, wherein one path enters the reference arm, and the other path enters the measuring arm; the light returned by the reference arm and the measuring arm enters the spectrometer after passing through the optical fiber coupler. The invention can realize the imaging of the cornea and retina of the eye by only adding one beam splitting element and one beam combining element and using a single reference arm, does not need to additionally add a dynamic focusing mechanism, an optical path adjusting mechanism and a plurality of reference arms, finally enters a spectrometer for imaging, realizes the synchronous measurement of the cornea and retina of the eye by an optimized optical design, does not need to additionally use expensive optical elements and electronic equipment, and has low cost.
Description
Technical Field
The invention relates to the technical field of optical imaging, in particular to an optical coherence tomography device for synchronously measuring cornea and retina of an eye.
Background
The ocular axis is the distance from the anterior surface of the cornea to the retinal pigment epithelium layer, and its components include the cornea thickness, anterior chamber depth, lens thickness, vitreous cavity length, and macular retinal nerve epithelium layer thickness. Clinically, various diseases such as cataract, ametropia, strabismus, amblyopia, glaucoma, silicone eye, macular edema and the like are accompanied by changes in different degrees of the eye axis, and understanding the changes of the eye axis at each stage is helpful for diagnosis and treatment of the diseases. Eye axial parameters such as corneal thickness, anterior chamber depth, lens thickness, vitreous thickness, and axial length, as shown in fig. 1.
Cataract is the leading cause of blindness worldwide, and since 2017, at least 9500 ten thousand people worldwide are affected by cataract. The cataract incidence rate of people 60 to 89 years old in China is about 80 percent, and the cataract incidence rate of people over 90 years old reaches over 90 percent. Cataract surgery is a common means to solve this problem, and the accuracy of eye biometric measurements prior to surgery will directly relate to the accuracy of the intraoperative intraocular lens power, while also closely relating to the postoperative refractive error, and an axial measurement error of 1mm will result in a refractive change of about 2.5D.
Myopia is one of the most widespread and common ocular disorders worldwide. Currently, global myopia prevalence is increasing, and by 2050 worldwide there will be 47.58 million people with myopia (about 49.8% of the global population), where high myopia will reach 9.38 million people (about 9.8% of the global population). With the current popularization of mobile internet, tablet personal computers and mobile phones, the phenomenon of eye disease reduction is becoming serious. The myopia of teenagers in China is very serious, the prevalence rate of myopia of students is always high, children aged 6 are 14.5%, pupil is 36.0%, junior middle school students are 71.6%, and senior middle school students are 81.0%. The length of the eye axis is a structural parameter which has a strong correlation with myopia formation, the degree of myopia has positive correlation with the length of the eye axis, and the length of the eye axis is an important basis for distinguishing true myopia from pseudomyopia. The eye biological parameters of the myopic patient before and after the excimer operation change, the preoperative eye axis measurement is favorable for the prediction of the postoperative refractive state, the thickness of the postoperative cornea is thinned, and the non-contact eye axis length measurement can avoid pressurizing the cornea of the eye to ensure accurate measurement and reduce the infection opportunity and cornea damage. In addition, changes such as an increase in the thickness of the lens after excimer surgery, a decrease in the depth of the anterior chamber, etc. have an influence on the calculation of the number of intraocular lenses for patients who need cataract surgery, so accurate measurement is indispensable.
Glaucoma is the second generally blinding eye disease faced by humans at present, and the biological structure of the eye tends to change after onset. Primary angle closure glaucoma increases corneal curvature, lens thickness, and decreases anterior chamber depth and ocular axis. Studies show that the ratio of the thickness of the primary angle-closure glaucoma crystals to the length of the eye axis is increased, and the ratio of the anterior chamber depth to the eye axis is reduced, thereby providing a basis for screening and early diagnosis of glaucoma patients.
In summary, accurately acquiring the axial parameters of the eye and finding out the changes of the parameters in time is a data base for diagnosis and treatment of ophthalmic diseases, and has important significance for treatment of intraocular diseases.
The axial parameters of the eye comprise the surface of the cornea of the eye to the pigment epithelium layer of the retina, and the measurement method mainly comprises three types of measurement methods based on ultrasound, measurement methods based on coherent light interferometry and optical coherence tomography (Optical Coherence Tomography, OCT) measurement methods based on a low-coherence light source. Most of ophthalmic advanced detection equipment in China need to be imported from abroad at present, most of ultrasonic detection methods are independently developed, the ultrasonic frequency is 8-10MHz or even higher, and the resolution is about 0.1mm, so that the depth and higher resolution requirements for observing eye tissues are met. The ultrasonic measurement method needs ocular surface anesthesia before measurement, the pressure formed by the contact of the measurement probe with the cornea can influence the measurement result, and meanwhile, the measurement result is easily subjectively influenced by an operator, and the measurement accuracy is low, the speed is low and the efficiency is low. The measurement method based on coherent light interferometry realizes measurement by measuring reflected and scattered back light interferometry signals of cornea and retina of an eye, has higher measurement accuracy and reliability compared with the measurement method based on ultrasound, but still has the problems of lower measurement accuracy, poorer numerical repeatability, higher measurement error rate and the like when measuring eyes with dense nuclear cataract and eyes with ophthalmic diseases. The measurement method based on OCT has the advantages of higher measurement accuracy, higher numerical repeatability, lower measurement error rate and the like, and the interference signal is processed to obtain images of cornea and retina of the eye, compared with the ultrasonic measurement method, the method has the following characteristics: ① The contact with the cornea to be measured is not needed during measurement, so that surface anesthesia is not needed, discomfort of a patient is avoided, and the risk of abrasion or infection of the cornea is reduced; ② With better measurement repeatability and higher axial resolution (0.01 mm, 0.lmm relative to the ultrasound measurement method); ③ The method can be used for measuring the length of the eye axis of eyes in different states, such as artificial lens eyes, silicone eyes and the like with different materials; ④ Because the doctor does not need to directly use the probe, the human interference factor is greatly reduced, and the individual difference caused by different operators during measurement is avoided. Compared with the traditional coherent light interferometry, the measurement method based on OCT has the following characteristics: ① OCT adopts a low-coherence light source, and a maximum value of light intensity appears in an output interference spectrogram, wherein a stripe corresponding to the maximum value is called a central stripe: only when the optical path difference between the measuring arm and the reference arm is smaller than the coherence length of the light source, an interference image is obtained at the output end. The position of the central stripe can be calibrated through the characteristics, and the measurement of the target physical quantity is realized by measuring the change of the optical path difference of the two arms; ② OCT systems based on low coherence light sources mainly measure the error from the positioning accuracy of the center fringes. Positioning accuracy can be improved by using a light source with a wider line width. The wider the spectral line width of the light source is, the worse the coherence is, the narrower the interference spectrum is, so that the position of the central stripe is easier to locate, and the technical advantages of high resolution and high sensitivity are achieved; ③ The actual output interference signal condition is also related to factors such as output power stability of a system light source, end surface reflection effect, loss of an optical fiber coupler and other equipment, bending jitter of an optical fiber and the like, and the current technical level can meet the demands of ophthalmic application. Therefore, the measurement method based on OCT has become the focus and hot spot of research and application in the field of eye anterior segment and retina measurement at present, and has the characteristics of real-time performance, high precision and non-contact.
However, in the measurement method based on OCT, because a broadband light source and a spectrometer are adopted to construct a system, the interference length is shorter and the imaging depth is limited due to the limitations of the wavelength of the broadband light source, the grating resolution of the spectrometer, the resolution of a spectrum acquisition camera and the like. In order to improve the imaging range of the OCT system, zhou et al propose an OCT system based on a dual reference arm and dual focus point and use it for anterior ocular segment imaging, focus two part light beams on cornea and lens bottom of eye respectively through dual reference arm and dual focus point, image the whole anterior ocular segment, this study applies the dual reference arm method to anterior ocular segment imaging, can realize anterior and posterior surface imaging of cornea and lens, prove the prospect of multi-reference arm method in long distance imaging and measurement application of human eye, offer new research direction for eye axial length measurement. Zhu et al propose an OCT system with selectable reference arms for the problem that OCT imaging sensitivity decreases with depth index, and the OCT system is also in a double-reference-arm mode, and the switching of the double reference arms is realized by changing the light path through a scanning galvanometer. Ruggeri et al propose a three reference arm SD-OCT system for realizing human eye imaging by image stitching. Fan et al propose a dual light source and dual reference arm SD-OCT system that uses light sources with center wavelengths of 840nm and 1050nm, respectively, to focus the focal points of the different light sources on the cornea and retina of the eye, respectively, to achieve human eye imaging. Although the OCT system can realize human eye imaging, multiple reference arms are needed to splice or dynamically focus or multifocal or add a moving mechanism to change optical path and other complex modes to realize comprehensive measurement of cornea and retina, which increases system complexity and leads to system errors due to excessive reference arms and further leads to measurement errors.
Disclosure of Invention
The invention aims to solve the technical problems that the interference length of an OCT system in the prior art is short and the imaging depth is limited, and provides an optical coherence tomography device for synchronously measuring cornea and retina of an eye.
In order to solve the technical problems, the technical scheme of the invention is as follows:
an optical coherence tomography device for simultaneous measurement of cornea and retina of an eye, comprising: a low coherence light source, a fiber coupler, a reference arm, a measurement arm, and a spectrometer; the light emitted by the low-coherence light source is divided into two paths after passing through the optical fiber coupler, wherein one path enters the reference arm, and the other path enters the measuring arm; light returned by the reference arm and the measuring arm enters the spectrometer after passing through the optical fiber coupler;
The reference arm sequentially comprises the following components in the light path direction: a reference arm collimator lens, an achromatic glass, and a focusing lens, and a reference arm mirror;
The measuring arm includes: an cornea branch and a retina branch;
The retina branch circuit sequentially comprises the following components in the light path direction: the device comprises a first lens, a scanning galvanometer, a second lens, a beam splitting element, a third lens, a fourth lens, a beam combining element and a fifth lens;
The cornea branch circuit sequentially comprises the following components in the light path direction: the first lens, the scanning galvanometer, the second lens, the beam splitting element, a first reflecting mirror, a sixth lens, a seventh lens, an eighth lens, a second reflecting mirror, the beam combining element and the fifth lens; wherein the first lens, the scanning galvanometer, the second lens, the beam splitting element, the beam combining element and the fifth lens are shared by the cornea branch and the retina branch;
the light reaches the eye to be detected after passing through the cornea branch and the retina branch, and returns from the cornea branch and the retina branch after being reflected; in the retina branch, the scanning galvanometer is conjugated with the pupil of the eye to be detected; in the cornea branch, the scanning galvanometer is conjugated with a fifth lens;
And the reference beam reflected by the reference arm reflector and the detection beam reflected by the interface with different depths of the eye to be detected are converged in the optical fiber coupler and received by the spectrometer, the optical path difference between the reference arm and the measuring arm is interfered within a coherent length range of the light source, and finally the optical path difference enters the spectrometer for synchronous imaging.
In the technical scheme, the optical path difference of the two paths of light in the measuring arm in the air is between 0.5mm and 2 mm.
In the above technical solution, the beam splitting element and the beam combining element are respectively: a mirror or a semi-reflective semi-transmissive element;
If the reflection mirror is used, one scanning moment is incident to the reflection mirror to reflect into the cornea branch, and the other scanning moment deviates from the reflection mirror to transmit into the retina branch; if the element is a semi-reflective semi-transmissive element, the emitted light enters the cornea branch and the transmitted light enters the retina branch.
In the above technical solution, the beam splitting element and/or the beam combining element are: a D-type reflector, a stripe-shaped reflection and transmission lens with a reflection and transmission surface alternately arranged, a half-reflection and half-transmission lens or a wave-division plate.
In the above technical scheme, the low coherence light source is a super-continuum spectrum light emitting diode (SLD) light source with a wavelength range of 800-1100 nm.
In the above technical solution, the light path length between the beam splitting element and the first reflecting mirror is C2, and the light path length between the beam combining element and the second reflecting mirror is C1, then: the sum of C1 and C2 is equivalent to the length of the eye axis of the eye to be tested.
In the above technical solution, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are two cemented lenses with diameters smaller than 12.7mm, respectively.
In the above-described aspect, the diameters of the third lens, the fourth lens, the sixth lens, the seventh lens, and the eighth lens are respectively less than half of the diameters of the second lens and/or the fifth lens.
In the above technical solution, the scanning step length of the scanning galvanometer in the X direction satisfies half of the transverse resolution, and the scanning step length in the Y direction satisfies that each step is equal to the diameter of the cornea branch beam on the beam combining element.
In the above technical solution, the spectrometer is used for obtaining the distance between interference signal peaks of cornea, anterior chamber, crystalline lens and retina of the eye to be measured through the interference images collected synchronously, and obtaining the eye axis parameter.
The invention has the following beneficial effects:
The optical coherence tomography device for synchronously measuring the cornea and the retina of the eye can realize the imaging of the cornea and the retina of the eye by only adding one beam splitting element and one beam combining element and using a single reference arm, does not need to additionally add a dynamic focusing and optical path regulating mechanism and a plurality of reference arms, finally enters a spectrometer for imaging, realizes the synchronous measurement of the cornea and the retina of the eye through an optimized optical design, does not have additional expensive optical elements and electronic equipment, and has low cost.
The invention relates to an optical coherence tomography device for synchronously measuring cornea and retina, which is characterized in that the cornea and retina synchronously measure, two paths share a scanning vibrating mirror, and the information of the eye axis parameters can be obtained through data processing after one-time measurement.
The optical coherence tomography device for synchronously measuring the cornea and the retina of the eye has high speed, and can finish measurement by scanning the scanning galvanometer once, and the time is in the second level.
The optical coherence tomography device for synchronously measuring the cornea and the retina of the eye has good compatibility and can be applied to OCT of any spectral domain and OCT of sweep frequency source.
Drawings
The invention is described in further detail below with reference to the drawings and the detailed description.
Fig. 1 is a schematic diagram of ocular axis parameters.
Fig. 2 is a schematic diagram of a probe arm of an optical coherence tomography instrument for simultaneous measurement of cornea and retina of an eye according to the present invention. In the figure, A is a retinal branch; b is an cornea branch; c is the distribution position of the focusing light spots on the beam splitting element; d is the distribution position of the collimated light beam of the beam combining element; e is a schematic of the stepwise course of the OCT scanning process beam.
Fig. 3 is a schematic diagram showing the system configuration of an optical coherence tomography apparatus for simultaneous measurement of cornea and retina of an eye according to the present invention.
Fig. 4 is a schematic view of the Zemax optical path of the measuring arm. In the figure, A is a retinal branch; b is a schematic diagram of an cornea branch.
Fig. 5 is a schematic diagram of beam splitting and combining elements. In the figure, A is a component real object diagram; b is a D-type reflector graph used in the physical graph.
Fig. 6 is a schematic diagram of a human eye detection result. In the figure, the red solid line frame pointed at by A is respectively an anterior and posterior surface detection signal of the cornea of an eye, an anterior and posterior surface detection signal of the lens and a retina detection signal, a1, a2, a3 and a4 are respectively the length of an eye axis, the thickness of an eye cornea, the depth of an anterior chamber and the thickness of the lens from left to right, and cataract solid or impurities are suspected to be in the red solid line frame marked by A.
Fig. 7 is a schematic diagram of the results of eye cornea and retina synchronization measurements.
Reference numerals in the drawings denote:
L1-a first lens; l2-second lens, L3-third lens, L4-fourth lens, L5-fifth lens, L6-sixth lens, L7-seventh lens, L8-eighth lens, M1-first mirror, M2-second mirror.
Detailed Description
The invention is characterized in that:
Most of domestic eye axis multi-parameter measurement equipment is imported abroad, is high in price, is owned by only large hospitals, and is not popularized in small and medium-sized hospitals. In particular, there are few examples of multi-parameter measurements of the ocular axis using fiber optic interferometry. Therefore, the invention provides an optical coherence tomography device for synchronously measuring cornea and retina of an eye. The device only comprises a reference arm, does not need multiple focuses, does not need complex operations such as changing optical path and dynamic focusing, and the like; the method comprises the steps of adopting a beam splitting element and a beam combining element to realize synchronous scanning of cornea and retina of an eye in a biaxial structure, wherein the beam splitting element and the beam combining element are special placed reflectors, such as D-type reflectors, alternately penetrating or reflecting light on the beam splitting/beam combining element by controlling voltage values in the x direction and the y direction of scanning voltage, transmitting illumination light beams according to an original path through the beam splitting/beam combining element, and finally focusing on the retina, wherein the retina is called a retina branch; the illumination beam is reflected into another path that ultimately focuses on the cornea, known as the cornea branch. The optical path difference between the retina branch and the cornea branch is between 0.5mm and 2mm, and the two paths can share the same reference arm through reasonable matching design, finally enter the same spectrometer for interference imaging, and synchronously acquire images of cornea and retina of the eye. The non-common light path parts of the cornea branch and the retina branch are known, the length of the eye axis can be obtained by adding the measured optical path difference of the spectrometer, and other eye axis parameters can be obtained by calculating the optical path difference.
The invention is to add one-way measurement by a beam splitting element and a beam combining element on the basis that a measuring arm of a traditional low coherence OCT system has only one-way tomographic image, design two ways of cornea branches and retina branches to be parallel, and control the optical path difference of the two ways to be in the range of 0.5mm to 2 mm; wherein the measuring arm comprises an cornea branch and a retina branch; the beam passing through the measuring arm passes through the cornea, lens, vitreous body of the eye to the retina and returns along the original path, using the reference arm to interfere synchronously with the return scattered light of the cornea and retina branches. In fig. 2, the first lens L1, the scanning galvanometer, the second lens L2, the beam splitting element, the third lens L3, the fourth lens L4, the beam combining element and the fifth lens L5 form a retinal branch, and the path of the retinal branch is shown in fig. 2A. In fig. 2, the first lens L1, the scanning galvanometer, the second lens L2, the beam splitting element, the first mirror M1, the sixth lens L6, the seventh lens L7, the eighth lens L8, the second mirror M2, the beam combining element, and the fifth lens L5 form an cornea branch, and the path thereof is shown in fig. 2B. The first lens L1, the scanning galvanometer, the second lens L2, the beam splitting element, the beam combining element and the fifth lens L5 are shared by the cornea branch and the retina branch. The first lens L1 is a measuring arm collimator lens.
If the optical path difference between the return light of the measured human eye and the return light of the measuring arm is within the range of 0.5 mm-2 mm, the generated interference signal has the maximum light intensity, and the interference signals of the cornea and retina in the same reference arm are realized by equal length and parallel design of the two paths of optical paths, namely, the path length difference between the retina branch path in the figure 2A and the cornea branch path length in the figure 2B is controlled within the range of 0.5 mm-2 mm, and the sum of the length of the C1 path and the length of the C2 path in the figure 2B is required to be equal to the length of the eye axis, namely, C1+C2 is required to be within the range of 20 mm-30 mm. In order to realize the common light path design by using the same scanning galvanometer, the scanning path of the focusing point of the light beam on the beam splitting element is shown in fig. 2C, the scanning path of the collimated light beam on the beam combining element is shown in fig. 2D, the scanning beam step of the scanning galvanometer is shown in fig. 2E, the scanning step length in the X direction meets half of the transverse resolution, and the step length in the Y direction meets that each step is just equal to the diameter of the cornea branch light beam on the beam combining element. In the retina branch, the scanning galvanometer is conjugated with the pupil of the eye; in the cornea branch, the scanning galvanometer is conjugated with a fifth lens L5. And finally, interference images synchronously acquired by a spectrometer are used for calculating the distance between interference signal peaks of cornea, anterior chamber, crystalline lens, retina and the like of the eye to obtain eye axis parameters such as eye axis length and the like, wherein the accuracy is in the micrometer level, and the measurement time is in the second level.
The optical coherence tomography device for synchronously measuring the cornea and the retina of the eye realizes the synchronous measurement of the cornea and the retina of the eye by using one reference arm with extremely low cost by adding the optical design of the beam splitting element, the beam combining element and the double detection branches, and proves the feasibility of the scheme for measuring the parameters of the axis of the eye.
The optical coherence tomography device for synchronously measuring the cornea and the retina of the eye changes the problem of insufficient depth of the traditional OCT measurement method based on the low coherence light source, fully exerts the advantages of high sensitivity, high resolution, non-contact and the like of the low coherence interference technology, and realizes synchronous detection of the cornea and the retina of the eye.
On the basis that the traditional low coherence OCT can only realize retina measurement, the invention designs a set of eye axis parameter measurement system, researches the key technology thereof, obtains the eye axis length and the position information between all interfaces in eye tissues through the system, ensures that the traditional low coherence OCT has the capability of synchronously measuring cornea and retina of the eye on the basis of extremely low cost, and provides theoretical basis for diagnosis and treatment of ophthalmic diseases and the like.
The invention has the following characteristics:
1) The two-way parallel arrangement of the cornea branches and the retina branches shares a scanning galvanometer, and synchronous measurement of the cornea and the retina can be realized by using the arrangement, and the sum of the path length C1 and the path length C2 in the figure 2B is required to be equivalent to the length of the eye axis, namely, the sum of the path lengths C1 and C2 is in the range of 20mm to 30 mm.
2) The beam alternately passes through or reflects on the beam splitting and combining elements, such as the scan path of the beam at the focusing point on the beam splitting element as shown in fig. 2C, the scan path of the collimated beam on the combining element as shown in fig. 2D, and the scan beam step of scanning the galvanometer as shown in fig. 2E, but is not limited to the paths described in fig. 2C, 2D, and 2E.
3) The cornea branch and the retina branch use the configuration of the same reference arm, the optical path difference in the air is between 0.5mm and 2mm, the same reference arm is shared to enter the same spectrometer for synchronous imaging, and the parameters of the eye axis are calculated based on the calibrated common optical path part length and the optical path difference of two images in the spectrometer;
4) The two-way parallel arrangement is achieved by a beam splitting element and a beam combining element, wherein the beam splitting element and the beam combining element are element mirrors which are half reflective and half transmissive, such as D-type mirrors, so that half of the illumination beam is transmitted through the mirrors to form a retinal branch and the other half is reflected to an cornea branch, but is not limited to the case in fig. 2 (for example, reflective transmissive surfaces may also be alternately present).
5) The optical design of the cornea branch and the retina branch adopts a lens with half-inch lens or smaller size to form a 2-group 4f system, and the scanning galvanometer is conjugated with the pupil of the eye in the retina branch; in the cornea branch, the scanning galvanometer is conjugated with a fifth lens L5; the dimensions of the third lens L3, the fourth lens L4, the sixth lens L6, the seventh lens L7, and the eighth lens L8 are less than half of those of the second lens L2 and the fifth lens L5, so as to ensure that the parallel optical paths have enough placement space.
The present invention will be described in detail with reference to the accompanying drawings.
As shown in fig. 2 to 4, the optical coherence tomography apparatus for simultaneous measurement of cornea and retina of an eye of the present invention comprises: a low coherence light source, a fiber coupler, a reference arm, a measurement arm, and a spectrometer; light emitted by the low-coherence light source is divided into two paths after passing through the optical fiber coupler, wherein one path enters the reference arm, and the other path enters the measuring arm; the reference arm sequentially includes in the optical path direction: a reference arm collimator lens, a achromatic fused silica glass, and a focusing lens, and a reference arm mirror; the measuring arm includes: an cornea branch and a retina branch; the retinal branch comprises in order in the direction of the optical path: a first lens L1, a scanning galvanometer, a second lens L2, a beam splitting element, a third lens L3, a fourth lens L4, a beam combining element, and a fifth lens L5; the cornea branch of the eye sequentially comprises in the light path direction: a first lens L1, a scanning galvanometer, a second lens L2, a beam splitting element, a first mirror M1, a sixth lens L6, a seventh lens L7, an eighth lens L8, a second mirror M2, a beam combining element, and a fifth lens L5; the first lens L1, the scanning galvanometer, the second lens L2, the beam splitting element, the beam combining element and the fifth lens L5 are shared by the cornea branch and the retina branch.
The light reaches the eye to be detected after passing through the cornea branch and the retina branch, and returns from the cornea branch and the retina branch after being reflected; light returned by the reference arm and the measuring arm enters the spectrometer after passing through the optical fiber coupler; in the retina branch, a scanning galvanometer is conjugated with the pupil of the eye to be detected; in the cornea branch, the scanning galvanometer is conjugated with a fifth lens L5; the reference beam reflected by the reference arm reflector and the detection beam reflected by the interface with different depths of the eye to be detected are converged in the optical fiber coupler and received by the spectrometer, the optical path difference between the reference arm and the measuring arm is interfered within a coherent length range of the light source, and finally the interference is transmitted into the spectrometer for synchronous imaging.
The following describes the technical scheme of the invention in detail.
1. System composition
The basic system constitution of the optical coherence tomography apparatus for simultaneous measurement of cornea and retina of eye of the present invention based on low coherence OCT technique is shown in fig. 3, and the system comprises: the device comprises a low-coherence light source, an optical fiber coupler, a scanning galvanometer, a beam splitting element, a beam combining element and a double-light-path lens group. Light emitted by the low-coherence light source is divided into two paths through the optical fiber coupler, wherein one path enters the reference arm, and the other path enters the measuring arm. The reference arm includes: a reference arm collimator lens, achromatic fused silica glass, a focusing lens, and a reflecting mirror; the measuring arm includes: the measuring arm comprises a measuring arm collimating lens, a scanning galvanometer, a beam splitting element, a beam combining element and two parallel paths (an cornea branch and a retina branch) formed by a plurality of groups of lenses. The reference beam returned by the reflector and the detection beam reflected by the interfaces with different depths of the eye to be detected are converged in the optical fiber coupler and received by the spectrometer, the optical path difference between the reference arm and the measuring arm is interfered when the optical path difference is within a coherent length range of the light source, the optical path difference between two paths in the measuring arm is between 0.5mm and 2mm, interference signals of the cornea and retina of the eye are ensured to be in a measuring depth range of the spectrometer, and finally the interference signals enter the spectrometer to synchronously image, a plurality of stronger interference signals are obtained in the spectrometer at the same time, the position information reflects the relative spatial positions of different structures in the eye tissue to be detected, and the position information of the eye tissue structure is obtained after data processing.
The low coherence light source in the system is selected mainly by considering the transmissivity of eye tissue to light with different wavelengths, the main component in the eye tissue is water, and the light absorption characteristic of the water leads to larger attenuation of the light source with the wavelength being far greater than 800 nm. Throughout the scan, the power loss due to water absorption was about 48% at the 1060nm wavelength light source and about 5% at the 800nm wavelength light source. However, according to the american national standards institute (American National Standard Institute, ANSI) standard, the maximum allowable exposure of the human eye increases with increasing wavelength, and thus the sensitivity can be improved by using higher incident power at longer wavelengths. The light source in the wavelength range of 1000-1100 nm has smaller attenuation in the opaque eye medium and has certain applicability to the condition that the refractive medium in the eye is turbid and the like. Therefore, any SLD light source with the wavelength range of 800-1100 nm is selected as a system light source, and the incident light power at the cornea of the eye is controlled to meet ANSI standards.
2. Principle of system operation
The collected interference signals can reconstruct the reflectivity envelope of the depth analysis in the focusing direction of the detection light through Fourier transformation. Taking one of the paths as an example, the interference spectrum signal can be expressed as:
；
Wherein i is the imaginary part of a complex number, the distance between the measuring arm and the end face of the optical fiber coupler is Z, the corresponding sample backward reflection coefficient is a (Z), the distance between the reference arm and the end face of the optical splitter is R, the reference arm backward reflection coefficient is a (R), S (k) is the power spectral density of the light source, k is the wave number, ，For angular frequency 2f，Is the speed of light. It can be assumed that the amplitude and phase are not modulated after the light source enters the reference arm, i.e., let a (R) =1. Meanwhile, the common reference plane of the measuring arm and the reference arm is set at the reference arm reflector position, so that R=0 exists, and the distance between each reflecting surface in the sample and the common reference plane is recorded as Z (the reference mirror virtual image position), so that a simplified interference spectrum signal is obtained:
；
Wherein, The inverse fourier transform of a (k) is the axial emissivity distribution a (Z) of the sample, and a× (k) is the conjugate of a (k).
；
Wherein,Is the envelope of the autocorrelation function of the light source, i.e. the power spectral density of the light sourceIs an inverse transform of (a).Is a Gaussian curve, inverse transformation thereofAlso a gaussian curve.The Full Width Half Maximum (FWHM) becomes a major determinant of the axial resolution of the system. The sample information obtained by the inverse Fourier transform is accompanied by not only the sample image, but also related noise such as a direct current term and a sample autocorrelation term.The dc term at zero optical path z=0, which is the autocorrelation term of the reference arm, is the portion of the spectral signal where the intensity is the greatest.The self-coherent term for each depth information of the sample is distributed near the zero optical path and has relatively small amplitude. The DC term and the sample autocorrelation term are filtered to obtain depth information a (z) and a (-z) of the sample, which are a set of images symmetrical about the zero optical path, and in order to prevent the aliasing phenomenon, the sample is usually adjusted to one side of the zero optical path, i.e. one is introduced relative to the zero optical pathAlthough offset can be avoided, this would result in a system with a half reduction in detection depth. For the double interference imaging of the device, the optical path difference between the cornea branch and the retina branch is designed, namely the device is introducedThe offset is different in magnitude, so that the positions of the cornea image and the retina image are separated in the z direction, and the two images are synchronously acquired in one spectrometer. Because the signal to noise ratio of the image is reduced with the increase of the introduced bias amplitude, the used spectrometer is custom designed to ensure the imaging depth of the double fields, and the introduction of a full-range spectrometer or sweep OCT is a solution.
3. Data acquisition method
The acquisition of data is acquired and processed by customized software OCTViewer, and the software mainly realizes the function of generating a sawtooth wave driving signal so as to control the two-dimensional scanning of the scanning galvanometer; the spectrum signals of the spectrometer are synchronously collected, and the linear array camera operates at a maximum readout rate of 70 kHz. The output of the camera was digitized at a sampling rate of 5MS/s per channel using a data acquisition board with 12-bit resolution. The sampled data is continuously transferred to the computer memory. Each set of 512 data points acquired by the camera is subjected to a discrete fourier transform to produce an axial depth tomographic image of the sample. The quality of the acquired image can be immediately assessed by GPU acceleration to provide real-time visualization of the OCT image; saving the acquired image facilitates later off-line image processing and analysis. The scanning range of the sawtooth wave is consistent with the field of view of the imaging system, and the step length meets the Nyquist sampling theorem and is smaller than half of the transverse resolution. These synchronous scanning signals are converted into voltage control waveforms by NIDAQ and then sent to the drivers of the two-dimensional galvanometer. Two-dimensional imaging for 512 x 512 pixels can reach over hundred hertz.
All devices in the optical system are commercial devices and no custom processing is required. The light source selects SLD broadband light source M-T-850-HP-I of SUPERRUM company, the optical fiber coupler, the circulator, the lens and the reflector all select products of Thorlabs company, the scanning galvanometer selects GVS002 two-dimensional scanning galvanometer of Thorlabs company, the driving voltage card is NI6221 of America NI company, the linear array camera selects E2V-Octoplus-2K-W4/EV71YEM4CL2014-BA9 of America NI company, the grating selects WP-HD1800/840 of America Wasatch Photonics company, the columnar reflector adopts Edmund company products, the serial number #54-092, the beam splitting element and the beam combining element are D type reflectors, the selection based on the above devices is optimized by Zemax, the double-path design result of the measuring arm is shown in figure 4, and the beam splitting and beam combining element is shown in figure 5.
To demonstrate the feasibility of the device, we measured multiple sets of human eye experiments, the measurement results are shown in fig. 6.
From the measurement results, the eye axis measurement system based on the low-coherence light interference principle realizes the measurement of the eye axis by double-light-path interference, can obtain main parameters such as the length of the eye axis, the thickness of the cornea, the thickness of the anterior segment of the eye, the thickness of the crystalline lens and the like, and has the advantages of high accuracy and high repeatability. The invention provides a new measurement scheme for preventing and controlling early pseudomyopia and myopia, provides a new technical scheme for the research and development of the ocular axis biological parameter measuring instrument, and has important practical significance.
In the specific embodiment of the present invention, the beam splitting element and the beam combining element may have other alternatives, such as a customized stripe-shaped reflective transmissive lens, a half-reflective semi-transmissive lens, and a beam splitting plate. The three schemes have simpler scanning routes than the invention, but the signal to noise ratio is not as good as the above embodiment because the semi-reflective and semi-transparent sheet can leak light. The resolution of the sub-waveplate is not as good as the above-described embodiments due to the sacrifice of the bandwidth of the light source. The striped reflective transmissive mirror requires special customization and is not as cost effective as the above-described embodiments.
The optical coherence tomography device for synchronously measuring the cornea and the retina of the eye changes the problem of insufficient depth of the traditional OCT measurement method based on the low coherence light source, fully exerts the advantages of high sensitivity, high resolution, non-contact and the like of the low coherence interference technology, and realizes synchronous detection of the cornea and the retina of the eye. Based on the traditional low coherence OCT, only retina measurement can be realized, a set of eye axis parameter measurement system is designed, the key technology is researched, the eye axis length and the position information between all interfaces in eye tissues are obtained through the system, the traditional low coherence OCT has the capability of synchronously measuring cornea and retina on the basis of extremely low cost, and a theoretical basis is provided for diagnosis and treatment of ophthalmic diseases and the like.
The optical coherence tomography device for synchronously measuring the cornea and the retina of the eye can realize the imaging of the cornea and the retina of the eye by only adding one beam splitting element and one beam combining element and using a single reference arm, does not need to additionally add a dynamic focusing and optical path regulating mechanism and a plurality of reference arms, finally enters a spectrometer for imaging, realizes the synchronous measurement of the cornea and the retina of the eye through an optimized optical design, does not have additional expensive optical elements and electronic equipment, and has low cost.
The invention relates to an optical coherence tomography device for synchronously measuring cornea and retina, which is characterized in that the cornea and retina synchronously measure, two paths share a scanning vibrating mirror, and the information of the eye axis parameters can be obtained through data processing after one-time measurement.
The optical coherence tomography device for synchronously measuring the cornea and the retina of the eye has high speed, and can finish measurement by scanning the scanning galvanometer once, and the time is in the second level.
The optical coherence tomography device for synchronously measuring the cornea and the retina of the eye has good compatibility and can be applied to OCT of any spectral domain and OCT of sweep frequency source.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (7)
1. An optical coherence tomography device for simultaneous measurement of cornea and retina of an eye, comprising: a low coherence light source, a fiber coupler, a reference arm, a measurement arm, and a spectrometer; the light emitted by the low-coherence light source is divided into two paths after passing through the optical fiber coupler, wherein one path enters the reference arm, and the other path enters the measuring arm; light returned by the reference arm and the measuring arm enters the spectrometer after passing through the optical fiber coupler;
The reference arm sequentially comprises the following components in the light path direction: a reference arm collimator lens, an achromatic glass, and a focusing lens, and a reference arm mirror;
The measuring arm includes: an cornea branch and a retina branch;
The retina branch circuit sequentially comprises the following components in the light path direction: a first lens (L1), a scanning galvanometer, a second lens (L2), a beam splitting element, a third lens (L3), a fourth lens (L4), a beam combining element and a fifth lens (L5);
The cornea branch circuit sequentially comprises the following components in the light path direction: the first lens (L1), the scanning galvanometer, the second lens (L2), the beam splitting element, a first reflecting mirror (M1), a sixth lens (L6), a seventh lens (L7), an eighth lens (L8), a second reflecting mirror (M2), the beam combining element and the fifth lens (L5); wherein the first lens (L1), the scanning galvanometer, the second lens (L2), the beam splitting element, the beam combining element, and the fifth lens (L5) are common to the cornea branch and the retina branch;
the light reaches the eye to be detected after passing through the cornea branch and the retina branch, and returns from the cornea branch and the retina branch after being reflected; in the retina branch, the scanning galvanometer is conjugated with the pupil of the eye to be detected; in the cornea branch, the scanning galvanometer is conjugated with a fifth lens (L5);
The reference beam reflected by the reference arm reflector and the detection beam reflected by interfaces with different depths of the eye to be detected are converged in the optical fiber coupler and received by the spectrometer, the optical path difference between the reference arm and the measuring arm is interfered within a coherent length range of a light source, and finally the optical path difference enters the spectrometer for synchronous imaging;
the optical path difference of two paths of light in the measuring arm in the air is between 0.5mm and 2 mm;
A light path length between the beam splitting element and the first reflecting mirror (M1) is C1, and a light path length between the beam combining element and the second reflecting mirror (M2) is C2, then: the sum of C1 and C2 is equal to the length of the eye axis of the eye to be measured;
the diameters of the third lens (L3), the fourth lens (L4), the sixth lens (L6), the seventh lens (L7) and the eighth lens (L8) are respectively less than half of the diameters of the second lens (L2) and/or the fifth lens (L5).
2. The optical coherence tomography instrument for simultaneous measurement of the cornea and retina of an eye of claim 1, wherein said beam splitting element and said beam combining element are respectively: a mirror or a semi-reflective semi-transmissive element;
If the reflection mirror is used, one scanning moment is incident to the reflection mirror to reflect into the cornea branch, and the other scanning moment deviates from the reflection mirror to transmit into the retina branch; if the element is a semi-reflective semi-transmissive element, the emitted light enters the cornea branch and the transmitted light enters the retina branch.
3. The optical coherence tomography instrument for simultaneous measurement of the cornea and retina of an eye according to claim 2, wherein the beam splitting element and/or the beam combining element are: a D-type reflector, a stripe-shaped reflection and transmission lens with a reflection and transmission surface alternately arranged, a half-reflection and half-transmission lens or a wave-division plate.
4. The optical coherence tomography instrument for simultaneous measurement of the cornea and retina of an eye according to claim 1, wherein the low coherence light source is a super-continuum light emitting diode light source in a wavelength range of 800-1100 nm.
5. The optical coherence tomography instrument for synchronous measurement of the cornea and retina of an eye according to claim 1, characterized in that the first lens (L1), the second lens (L2), the third lens (L3), the fourth lens (L4), the fifth lens (L5), the sixth lens (L6), the seventh lens (L7) and the eighth lens (L8) are each a cemented doublet with a diameter of less than 12.7 mm.
6. The optical coherence tomography instrument for simultaneous measurement of the cornea and retina of an eye of claim 1, wherein said scanning galvanometer has a scanning step in the X-direction that is half the lateral resolution and a scanning step in the Y-direction that is each equal to the diameter of said cornea branch beam on said beam combining element.
7. The optical coherence tomography instrument for simultaneous measurement of the cornea and retina of an eye according to any one of claims 1-6, wherein the spectrometer is adapted to obtain the eye axis parameters from the interference images acquired simultaneously to obtain the distances between the interference signal peaks of the cornea, anterior chamber, lens and retina of the eye to be measured.
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