CN118078203A - Optical coherence tomography device for synchronously measuring cornea and retina of eye - Google Patents

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

Optical coherence tomography device for synchronous measurement of cornea and retina

Technical Field

The invention relates to the technical field of optical imaging, and in particular to an optical coherence tomography device for synchronously measuring cornea and retina.

Background technique

The axial length of the eye is the distance from the front surface of the cornea to the retinal pigment epithelium. Its components include corneal thickness, anterior chamber depth, lens thickness, vitreous cavity length, and thickness of the retinal neuroepithelium in the macula. Clinically, many diseases such as cataracts, refractive errors, strabismus, amblyopia, glaucoma, silicone oil eye, and macular edema are accompanied by varying degrees of changes in the axial length of the eye. Understanding the changes in the axial length at each stage is helpful for the diagnosis and treatment of the disease. Eye axial parameters, such as corneal thickness, anterior chamber depth, lens thickness, vitreous thickness, and axial length, are shown in Figure 1.

Cataract is the leading cause of blindness in the world. Since 2017, at least 95 million people worldwide have been affected by cataracts. In my country, the incidence of cataracts in people aged 60 to 89 is about 80%, while the incidence of cataracts in people over 90 is more than 90%. Cataract surgery is a common means to solve this problem. The accuracy of eye biometry before surgery will directly affect the accuracy of the intraocular lens implanted during surgery, and is also closely related to the refractive error after surgery. An axial measurement error of 1mm will result in a refractive error of about 2.5D.

Myopia is one of the most widespread and common eye diseases in the world. At present, the prevalence of myopia is gradually increasing worldwide. By 2050, there will be 4.758 billion people with myopia in the world (about 49.8% of the world's population), of which 938 million will have high myopia (about 9.8% of the world's population). With the popularization of mobile Internet, tablet computers, and mobile phones, the phenomenon of younger eye diseases is becoming more and more serious. The myopia situation among young people in my country is very serious. The prevalence of myopia among students has remained high, with 14.5% for 6-year-old children, 36.0% for primary school students, 71.6% for junior high school students, and 81.0% for high school students. Axial length is a structural parameter that is strongly associated with the formation of myopia. The degree of myopia is positively correlated with axial length. At the same time, axial length is also an important basis for distinguishing true myopia from false myopia. The ocular biological parameters of myopic patients change before and after excimer surgery. Preoperative axial length measurement helps predict the postoperative refractive state. The corneal thickness becomes thinner after surgery. The use of non-contact axial length measurement can avoid pressurizing the cornea, making the measurement accurate and reducing the chance of infection and corneal damage. In addition, changes such as increased lens thickness and reduced anterior chamber depth after excimer surgery affect the calculation of intraocular lens power in patients who need cataract surgery, so accurate measurement is essential.

Glaucoma is the second most common blinding eye disease faced by humans. After the onset of the disease, the biological structure of the eye often undergoes certain changes. In primary angle-closure glaucoma, the corneal curvature and lens thickness increase, and the anterior chamber depth and axial length decrease. Studies have shown that in primary angle-closure glaucoma, the ratio of lens thickness to axial length increases, and the ratio of anterior chamber depth to axial length decreases, providing a basis for the screening and early diagnosis of glaucoma patients.

In summary, accurately acquiring the axial parameters of the eye and timely detecting the changes in these parameters are the data basis for the diagnosis and treatment of ophthalmic diseases, and are of great significance for the treatment of intraocular diseases.

The axial parameters of the eye include the corneal surface to the retinal pigment epithelium. The measurement methods are mainly divided into three categories: ultrasound-based measurement methods, coherent light interference-based measurement methods, and optical coherence tomography (OCT) measurement methods based on low-coherence light sources. At present, most of the advanced ophthalmic detection equipment in China needs to be imported from abroad, and most of the independently developed detection methods are ultrasonic detection methods, which use ultrasonic frequencies of 8-10MHz or even higher and resolutions of about 0.1mm to meet the depth and high resolution requirements required for observing eye tissues. The ultrasonic measurement method requires ocular surface anesthesia before measurement. The pressure formed by the measurement probe contacting the cornea will affect the measurement results. At the same time, the measurement results are easily affected by the operator's subjective influence, and its measurement accuracy is low, the speed is slow, and the efficiency is low. The measurement method based on coherent light interference measures the interference signals of the reflected and scattered light from the cornea and retina. Compared with the ultrasound-based measurement method, it has higher measurement accuracy and reliability. However, when measuring human eyes with dense nuclear cataracts and human eyes with ophthalmic diseases, there are still problems such as low measurement accuracy, poor numerical repeatability, and high measurement error rate. The measurement method based on OCT has the advantages of high measurement accuracy, high numerical repeatability and low measurement error rate. After processing the interference signal, the images of the cornea and retina are obtained. Compared with the ultrasonic measurement method, it has the following characteristics: ① It does not need to contact the cornea to be measured during measurement, so surface anesthesia is not required, which avoids patient discomfort and reduces the risk of corneal abrasion or infection; ② It has better measurement repeatability and higher axial resolution (±0.01mm, compared with ±0.1mm of the ultrasonic measurement method); ③ It can be used to measure the axial length of eyes in different states, such as artificial lens eyes and silicone oil eyes of different materials; ④ Since the physician does not need to use the probe directly, the human interference factor is greatly reduced, avoiding individual differences caused by different operators during measurement. Compared with the traditional coherent light interferometry measurement method, the measurement method based on OCT has the following characteristics: ① OCT uses a low-coherence light source, and a maximum light intensity will appear in the output interference spectrum. The stripe corresponding to this maximum is called the central stripe: only when the optical path difference between the measuring arm and the reference arm is less than the coherence length of the light source, the interference image will be obtained at the output end. This feature can be used to calibrate the position of the central stripe, and the target physical quantity can be measured by measuring the change in the optical path difference between the two arms; ② The main measurement error of the OCT system based on low-coherence light source comes from the positioning accuracy of the central stripe. The positioning accuracy can be improved by using a light source with a wider spectral line width. The wider the spectral line width of the light source, the worse its coherence, and the narrower the interference spectrum, so that the position of the central stripe is easier to locate, with the technical advantages of high resolution and high sensitivity; ③ The actual output interference signal is also related to factors such as the output power stability of the system light source, the end face reflection effect, the loss of the fiber coupler and other equipment, and the bending jitter of the fiber. At the current technical level, these parameters can meet the needs of ophthalmic applications. Therefore, the measurement method based on OCT has become the focus and hot spot of research and application in the field of anterior segment and retinal measurement, with the characteristics of real-time, high precision and non-contact.

However, the OCT-based measurement method uses a broadband light source and a spectrometer to build the system. The wavelength of the broadband light source and the grating resolution of the spectrometer and the resolution of the spectral acquisition camera are limited, resulting in a short interference length and limited imaging depth. In order to improve the imaging range of the OCT system, Zhou et al. proposed an OCT system based on dual reference arms and dual focal points for anterior segment imaging. The dual reference arms and dual focal points are used to focus the two parts of the light beam on the cornea and the bottom of the lens respectively to image the entire anterior segment. This study applied the dual reference arm method to anterior segment imaging, which can realize the imaging of the front and back surfaces of the cornea and lens, and proved the prospect of the multi-reference arm method in long-distance imaging and measurement applications of the human eye, providing a new research direction for axial length measurement. In response to the problem that the sensitivity of OCT imaging decreases with the depth index, Zhu et al. proposed an OCT system with selectable reference arms. It is also in the form of dual reference arms, and the dual reference arm switching is realized by changing the optical path through the scanning galvanometer. Ruggeri et al. proposed a three-reference arm SD-OCT system for human eye imaging, which realizes human eye imaging through image stitching. Fan et al. proposed a dual-light source and dual-reference arm SD-OCT system, which uses light sources with central wavelengths of 840nm and 1050nm, respectively, and focuses different light sources on the cornea and retina to achieve human eye imaging. Although the OCT system can achieve human eye imaging, it requires complex methods such as splicing multiple reference arms or dynamic focusing or multi-focus or adding a mobile mechanism to change the optical path to achieve comprehensive measurement of the cornea and retina, which increases the complexity of the system and too many reference arms can easily introduce system errors, which in turn leads to measurement errors.

Summary of the invention

The present invention aims to solve the technical problems of the prior art that the interference length of the OCT system is short and the imaging depth is limited, and provides an optical coherence tomography device for synchronous measurement of the cornea and retina.

In order to solve the above technical problems, the technical solutions of the present invention are as follows:

An optical coherence tomography device for synchronous measurement of cornea and retina, comprising: a low-coherence light source, a fiber coupler, a reference arm, a measuring arm and a spectrometer; light emitted by the low-coherence light source is divided into two paths after passing through the fiber coupler, one of which enters the reference arm and the other enters the measuring arm; light returned from the reference arm and the measuring arm enters the spectrometer after passing through the fiber coupler;

The reference arm includes, in sequence in the direction of the optical path: a reference arm collimating lens, an achromatic glass, a focusing lens and a reference arm reflector;

The measuring arm comprises: a cornea branch and a retina branch;

The retinal branch includes, in order in the direction of the optical path: 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 includes, in order in the optical path direction: the first lens, the scanning galvanometer, the second lens, the beam splitter, the first reflector, the sixth lens, the seventh lens, the eighth lens, the second reflector, the beam combining element and the fifth lens; wherein the first lens, the scanning galvanometer, the second lens, the beam splitter, 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 tested after passing through the cornea branch and the retina branch, and returns from the cornea branch and the retina branch respectively after reflection; in the retina branch, the scanning galvanometer is conjugate with the pupil of the eye to be tested; in the cornea branch, the scanning galvanometer is conjugate with the fifth lens;

The reference light beam reflected by the reference arm reflector and the detection light beam reflected by the interfaces at different depths of the eye to be measured merge in the fiber coupler and are received by the spectrometer. The optical path difference between the reference arm and the measuring arm interferes within a coherence length range of the light source and finally enters the spectrometer for synchronous imaging.

In the above technical solution, the optical path difference between the two paths of light in the measuring arm in the air is between 0.5 mm and 2 mm.

In the above technical solution, the beam splitting element and the beam combining element are respectively: a reflector or a semi-reflective and semi-transparent element;

If it is a reflector, the light is incident on the reflector at one scanning moment and reflected into the cornea branch, and at another scanning moment it deviates from the reflector and is transmitted into the retina branch; if it is a semi-reflective and semi-transparent 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 is: a D-type reflector, a striped reflective and transmissive lens with alternating reflective and transmissive surfaces, a semi-reflective and semi-transmissive plate, or a wave splitting plate.

In the above technical solution, the low-coherence light source is a supercontinuum 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 reflector is C2, and the light path length between the beam combining element and the second reflector is C1. Then: the sum of C1 and C2 is equivalent to the axial length 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 doublet lenses with a diameter less than 12.7 mm respectively.

In the above technical solution, 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 lateral resolution, and the scanning step length in the Y direction satisfies that each step is equal to the diameter of the corneal branch light beam on the beam combining element.

In the above technical solution, the spectrometer is used to obtain the distances between the interference signal peaks of the cornea, anterior chamber, lens and retina of the eye to be tested through synchronously collected interference images, thereby obtaining the axial length parameters of the eye.

The present invention has the following beneficial effects:

The optical coherence tomography imaging device for synchronous measurement of the cornea and retina of the present invention only needs to add a beam splitter element and a beam combiner element, and can realize imaging of the cornea and retina using a single reference arm, without the need to additionally add dynamic focusing, optical path adjustment mechanisms and multiple reference arms, and finally enters a spectrometer for imaging. The synchronous measurement of the cornea and retina is realized through an optimized optical design, without the need for additional expensive optical elements and electronic equipment, and the cost is low.

The optical coherence tomography imaging device for synchronous measurement of cornea and retina of the present invention synchronously measures cornea and retina, and two paths share a scanning galvanometer. Eye axis parameter information can be obtained by processing data after one measurement.

The optical coherence tomography device for synchronously measuring cornea and retina of the present invention has high speed and can complete the measurement in seconds with one scan of the scanning galvanometer.

The optical coherence tomography device for synchronously measuring the cornea and retina of the present invention has good compatibility and can be applied to any spectral domain OCT and swept source OCT.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Figure 1 is a schematic diagram of eye axis parameters.

Figure 2 is a schematic diagram of the detection arm of the optical coherence tomography device for synchronous measurement of cornea and retina of the present invention. In the figure, A is the retinal branch; B is the cornea branch; C is the distribution position of the focused light spot on the beam splitter; D is the distribution position of the collimated light beam of the beam combining element; and E is a schematic diagram of the step-by-step route of the light beam during the OCT scanning process.

FIG. 3 is a schematic diagram of the system structure of the optical coherence tomography imaging device for synchronous measurement of the cornea and retina of the present invention.

Figure 4 is a schematic diagram of the Zemax optical path of the measuring arm, in which A is the retinal branch and B is the schematic diagram of the corneal branch.

Figure 5 is a schematic diagram of a beam splitting and combining element. A in the figure is a real picture of the element; B is a picture of the D-type reflector used in the real picture.

Figure 6 is a schematic diagram of the human eye detection results. In the figure, the red solid line frame pointed to by A is the corneal anterior and posterior surface detection signal, the lens anterior and posterior surface detection signal and the retinal detection signal from left to right, a1, a2, a3, a4 are the axial length, corneal thickness, anterior chamber depth and lens thickness, respectively. The red solid line frame marked by A is suspected to be cataract solid or impurities.

FIG. 7 is a schematic diagram of the synchronous measurement results of the cornea and retina.

The reference numerals in the figures indicate:

L1-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 reflector, M2-second reflector.

Detailed ways

The inventive concept of the present invention is:

Since most of the domestic multi-parameter measurement equipment for eye axis is imported from abroad, it is expensive and only large hospitals have it, and it is not popular in small and medium-sized hospitals. In particular, there are very few examples of using fiber optic interferometry to measure multi-parameters of eye axis. Therefore, the present invention proposes an optical coherence tomography device for synchronous measurement of cornea and retina. The device contains only one reference arm, does not require complex operations such as multi-focus, changing optical path and dynamic focusing; a beam splitter and a beam combiner are used to realize dual-axis structure synchronous scanning of cornea and retina, wherein the beam splitter and the beam combiner are specially placed reflectors, such as D-type reflectors, by controlling the voltage values of the scanning voltage in the x-direction and the y-direction to make the light alternately penetrate or reflect on the beam splitter/beam combiner, the illumination beam is transmitted through the original path and finally focused on the retina, which is called the retinal branch; the illumination beam is reflected into another path and finally focused on the cornea, which is called the corneal branch. The optical path difference between the retinal branch and the corneal branch is between 0.5mm and 2mm. Through reasonable matching design, the two paths can share the same reference arm and finally enter the same spectrometer for interferometric imaging to synchronously obtain images of the cornea and retina. The non-common optical path parts of the corneal branch and the retinal branch are known. The axial length can be obtained by adding the optical path difference measured by the spectrometer. Other axial parameters can be obtained by calculating the optical path difference.

The present invention intends to add a measurement through a beam splitter and a beam combiner on the basis of the conventional low-coherence OCT system, which has only one tomographic image in the measuring arm. The corneal branch and the retinal branch are designed to be parallel, and the optical path difference between the two paths is controlled within the range of 0.5 mm to 2 mm. The measuring arm of the OCT system is mainly composed of a low-coherence light source, a light coupler, a beam splitter, a beam combiner and a scanning galvanometer. The low-coherence light source emits light through the coupler and splits it into the measuring arm and the reference arm respectively; wherein the measuring arm includes a corneal branch and a retinal branch; the light beam passing through the measuring arm passes through the cornea, the lens, and the vitreous body to reach the retina and returns along the original path, and the reference arm is used to synchronize the interference with the return scattered light of the corneal branch and the retinal branch. In FIG2 , the first lens L1, the scanning galvanometer, the second lens L2, the beam splitter, the third lens L3, the fourth lens L4, the beam combiner and the fifth lens L5 constitute the retinal branch, and its path is shown in FIG2A . In FIG2 , the first lens L1, the scanning galvanometer, the second lens L2, the beam splitter, the first reflector M1, the sixth lens L6, the seventh lens L7, the eighth lens L8, the second reflector M2, the beam combining element and the fifth lens L5 constitute a cornea branch, and its path is shown in FIG2B . Among them, the first lens L1, the scanning galvanometer, the second lens L2, the beam splitter, 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 collimating lens for the measuring arm.

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 0.5mm~2mm, the generated interference signal intensity is the largest. The cornea and retina interference signals in the same reference arm are both the strongest by equal length and parallel design of the two optical paths, that is, the difference between the retinal branch path length in FIG2A and the cornea branch path length in FIG2B should be controlled within the range of 0.5mm to 2mm. At this time, the sum of the length of the C1 path and the length of the C2 path in FIG2B is required to be equivalent to the axial length of the eye, that is, C1+C2 is within the range of 20mm to 30mm. In order to realize the common optical path design using the same scanning galvanometer, the scanning path of the focus point of the light beam on the beam splitter element is shown in FIG2C, the scanning path of the collimated light beam on the beam combining element is shown in FIG2D, and the scanning beam steps of the scanning galvanometer are shown in FIG2E. The scanning step length in the X direction satisfies half of the lateral resolution, and the step length in the Y direction satisfies that each step is just equal to the diameter of the cornea branch light beam on the beam combining element. In the retinal branch, the scanning galvanometer is conjugated with the pupil of the eye; in the corneal branch, the scanning galvanometer is conjugated with the fifth lens L5. Finally, the distance between the interference signal peaks of the cornea, anterior chamber, lens, retina, etc. is calculated through the interference image synchronously collected by the spectrometer to obtain the axial length and other axial parameters, with an accuracy of micrometers and a measurement time of seconds.

The optical coherence tomography device for synchronous measurement of the cornea and retina of the present invention realizes synchronous measurement of the cornea and retina using one reference arm at a very low cost by adding a beam splitting element, a beam combining element and an optical design of a dual detection branch, and proves the feasibility of this scheme for measuring axial line parameters.

The optical coherence tomography device for synchronous measurement of the cornea and retina of the present invention will change the problem of insufficient depth of the existing OCT measurement method based on low-coherence light source, give full play to the advantages of low-coherence interference technology such as high sensitivity, high resolution, and non-contact, and realize synchronous detection of the cornea and retina.

Based on the fact that traditional low-coherence OCT can only achieve retinal measurement, the present invention designs an axial parameter measurement system, studies its key technologies, and obtains the axial length and the position information between the interfaces in the eye tissue through the system. On the basis of extremely low cost, the traditional low-coherence OCT has the ability to synchronously measure the cornea and retina, providing a theoretical basis for the diagnosis and treatment of ophthalmic diseases.

The present invention has the following characteristics:

1) The corneal branch and the retinal branch are configured in parallel, sharing a scanning galvanometer. This configuration can achieve synchronous measurement of the cornea and retina. It is required that the sum of the path lengths C1 and C2 in Figure 2B is equivalent to the axial length of the eye, that is, C1+C2 is in the range of 20mm to 30mm.

2) The light beam alternately passes through or reflects on the beam splitting and beam combining elements, such as the scanning path of the light beam at the focal point on the beam splitting element as shown in FIG. 2C , the scanning path of the collimated light beam on the beam combining element as shown in FIG. 2D , and the scanning beam steps of the scanning galvanometer as shown in FIG. 2E , but are not limited to the routes described in FIGS. 2C , 2D , and 2E .

3) The corneal branch and the retinal branch use the same reference arm configuration, the optical path difference in air is between 0.5mm and 2mm, and they share a reference arm to enter the same spectrometer for synchronous imaging. The axial parameters are calculated based on the calibrated length of the common optical path and the optical path difference between the two images in the spectrometer;

4) A dual-path parallel configuration is achieved through a beam splitter element and a beam combiner element, wherein the beam splitter element and the beam combiner element are both half-reflective and half-transmissive element reflectors, such as a D-type reflector, so that half of the illumination light beam passes through the reflector to form a retinal branch, and the other half is reflected to the cornea branch, but is not limited to the situation in FIG. 2 (for example, the reflective and transmissive surfaces may also appear alternately).

5) The optical design of the corneal branch and the retinal branch uses half-inch or smaller lenses to form two groups of 4f systems. In the retinal branch, the scanning galvanometer is conjugated with the pupil of the eye; in the corneal branch, the scanning galvanometer is conjugated with the fifth lens L5; the sizes 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 the sizes of the second lens L2 and the fifth lens L5 to ensure that there is enough space for the parallel optical paths.

The present invention is described in detail below with reference to the accompanying drawings.

As shown in Fig. 2-4, the optical coherence tomography device for synchronous measurement of cornea and retina of the present invention comprises: a low coherence light source, a fiber coupler, a reference arm, a measuring arm and a spectrometer; the light emitted by the low coherence light source is divided into two paths after passing through the fiber coupler, one of which enters the reference arm and the other enters the measuring arm; the reference arm comprises, in the direction of the optical path, a reference arm collimating lens, achromatic fused quartz glass and a focusing lens and a reference arm reflector; the measuring arm comprises: a cornea branch and a retina branch; the retina branch comprises, in the direction of the optical path, a first lens L 1. Scanning galvanometer, second lens L2, beam splitter, third lens L3, fourth lens L4, beam combining element and fifth lens L5; the cornea branch includes in the direction of the optical path: the first lens L1, scanning galvanometer, second lens L2, beam splitter, first reflector M1, sixth lens L6, seventh lens L7, eighth lens L8, second reflector M2, beam combining element and fifth lens L5; wherein, the first lens L1, scanning galvanometer, second lens L2, beam splitter, beam combining element and fifth lens L5 are shared by the cornea branch and the retina branch.

The light reaches the eye to be tested after passing through the cornea branch and the retina branch, and returns from the cornea branch and the retina branch respectively after reflection; the light returned from the reference arm and the measuring arm enters the spectrometer after passing through the fiber optic coupler; in the retina branch, the scanning galvanometer is conjugated with the pupil of the eye to be tested; in the cornea branch, the scanning galvanometer is conjugated with the fifth lens L5; the reference beam reflected by the reference arm reflector and the detection beam reflected by the interface of different depths of the eye to be tested converge in the fiber optic coupler and are received by the spectrometer, and the optical path difference between the reference arm and the measuring arm interferes within a coherent length range of the light source, and finally enters the spectrometer for synchronous imaging.

The technical solution of the present invention is described in detail below.

1. System composition

The basic system structure of the optical coherence tomography device for synchronous measurement of cornea and retina of the present invention based on low coherence OCT technology is shown in Figure 3. The system includes: a low coherence light source, a fiber coupler, a scanning galvanometer, a beam splitter, a beam combiner and a dual-light path lens group. The light emitted by the low coherence light source is divided into two paths through the fiber coupler, one path enters the reference arm and the other path enters the measurement arm. The reference arm includes: a reference arm collimating lens, achromatic fused quartz glass, a focusing lens and a reflector; the measurement arm includes: a measurement arm collimating lens, a scanning galvanometer, a beam splitter, a beam combiner and two parallel paths (cornea branch and retina branch) composed of multiple groups of lenses. The reference beam returned by the reflector and the detection beam reflected from the interface of different depths of the eye to be tested merge in the fiber coupler and are received by the spectrometer. Interference occurs when the optical path difference between the reference arm and the measuring arm is within a coherent length range of the light source. The two optical path differences in the measuring arm are between 0.5mm and 2mm, ensuring that the interference signals of the cornea and retina are within the measurement depth range of a spectrometer. Finally, they enter a spectrometer for synchronous imaging. At this time, multiple strong interference signals will be obtained in the spectrometer at the same time. This position information reflects the relative spatial positions of different structures inside the eye tissue to be tested. After data processing, the position information of the eye tissue structure is obtained.

The selection of low-coherence light sources in the system mainly considers the transmittance of eye tissue to light of different wavelengths. The main component of eye tissue is water, and the light absorption characteristics of water cause it to have a large attenuation for light sources with wavelengths much greater than 800nm. During the entire scanning process, the power loss caused by water absorption under the light source with a wavelength of 1060nm is about 48%, and the power loss caused by water absorption under the light source with a wavelength of 800nm is about 5%. However, according to the American National Standard Institute (ANSI) standard, the maximum allowable exposure of the human eye increases with the increase of wavelength, so the sensitivity can be improved by using higher incident power at longer wavelengths. The light source in the wavelength range of 1000~1100nm has less attenuation in opaque eye media and has certain applicability to situations such as turbidity of refractive media in the eye. Therefore, any SLD light source in the wavelength range of 800~1100nm is selected as the system light source to control the incident light power at the cornea to meet the ANSI standard.

2. System Working Principle

The collected interference signal can be transformed into a reflectivity envelope with depth resolution in the focusing direction of the detection light by Fourier transform. Taking one of the channels as an example, the interference spectrum signal can be expressed as:

;

Where i is the imaginary part of the complex number, the distance between the measuring arm and the end face of the fiber coupler is Z, the corresponding sample back reflection coefficient is a(Z), the distance between the reference arm and the end face of the beam splitter is R, the reference arm back reflection coefficient is a(R), S(k) is the power spectral density of the light source, k is the wave number, , is the angular frequency 2 f, is the speed of light. It can be assumed that the amplitude and phase of the light source are not modulated after entering the reference arm, that is, a(R)=1. At the same time, the common reference surface of the measuring arm and the reference arm is set at the position of the reference arm reflector, so R=0, and the distance between each reflective surface inside the sample and the common reference surface is recorded as Z (reference mirror virtual image position), and the simplified interference spectrum signal is obtained:

;

in, , 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).

;

in, is the envelope of the light source autocorrelation function, that is, the light source power spectrum density The inverse transform of . is a Gaussian curve, and its inverse transformation It is also a Gaussian curve. The full width at half maximum (FWHM) becomes the main determinant of the system's axial resolution. The sample information obtained by inverse Fourier transform is not only accompanied by the sample image, but also has related noise such as DC terms and sample autocorrelation terms. It is the DC term at zero optical path z=0. The DC term is the autocorrelation term of the reference arm and is the strongest part of the spectral signal. is the autocorrelation term of the sample's depth information, which is distributed near the zero optical path and has a relatively small amplitude. After filtering out the DC term and the sample autocorrelation term, we get the sample's depth information a(z) and a(-z), which are a set of mirror images symmetrical with respect to the zero optical path. In order to prevent this aliasing phenomenon from occurring, the sample is usually adjusted to one side of the zero optical path during imaging, that is, a relative to the zero optical path is introduced. Although the bias can be avoided, it will reduce the detection depth of the system by half. For the dual interference imaging of this device, by designing the optical path difference between the corneal branch and the retinal branch, that is, introducing Different offset sizes separate the positions of the corneal image and the retinal image in the z direction, thereby ensuring that the two images are collected synchronously in one spectrometer. As the introduced offset amplitude increases, the image signal-to-noise ratio decreases, so the spectrometer used should be custom designed to ensure the imaging depth of the dual field. Introducing a full-range spectrometer or swept-frequency OCT is a solution.

3. Data Collection Method

Data acquisition is acquired and processed by the customized software OCTViewer, which mainly generates sawtooth wave drive signals to control the two-dimensional scanning of the scanning galvanometer; synchronously collects the spectral signals of the spectrometer, and the linear array camera runs at a maximum readout rate of 70kHz. The output of the camera is 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. A discrete Fourier transform is performed on each group of 512 data points acquired by the camera to produce an axial depth tomographic image of the sample. GPU acceleration is used to provide real-time visualization of OCT images, so that the quality of the acquired images can be immediately evaluated; saving the acquired images facilitates later offline 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 size satisfies the Nyquist sampling theorem and is less than half of the lateral resolution. These synchronous scanning signals are converted into voltage control waveforms by NIDAQ and then sent to the driver of the two-dimensional galvanometer. At present, two-dimensional imaging for 512×512 pixels can reach more than 100 Hz.

All devices in this optical system are commercial devices, and no custom processing is required. The light source is SUPERLUM's SLD broadband light source M-T-850-HP-I, the fiber coupler, circulator, lens, and reflector are all Thorlabs products, the scanning galvanometer is Thorlabs' GVS002 two-dimensional scanning galvanometer, the driving voltage card is NI6221 from NI, USA, the line array camera is e2v's high-speed line array camera E2V-Octoplus-2K-W4/EV71YEM4CL2014-BA9, the grating is Wasatch Photonics' WP-HD1800/840, the cylindrical reflector is Edmund's product, number #54-092, the beam splitter and beam combiner are D-type reflectors, based on the selection of the above devices, the optimization is performed through Zemax, the dual-path design result of the measurement arm is shown in Figure 4, and the beam splitter and beam combiner used are shown in Figure 5.

In order to prove the feasibility of this device, we measured multiple groups of human eye experiments, and the measurement results are shown in Figure 6.

From the measurement results, it can be seen that the axial length measurement system based on the principle of low-coherence light interference of the present invention realizes the measurement of the axial length by dual-light path interference, and can obtain the main parameters such as axial length, corneal thickness, anterior segment thickness, and lens thickness, with the advantages of high accuracy and high repeatability. The present invention provides a new measurement scheme for the early prevention of pseudomyopia and myopia control, and provides a new technical scheme for the research and development of axial length biological parameter measuring instruments, which has important practical significance.

In a specific embodiment of the present invention, there may be other alternatives for the light splitting element and the beam combining element, such as using customized striped reflective and transmissive lenses, semi-reflective and semi-transmissive plates, and wave splitting plates. The scanning routes of these three solutions are simpler than those of the present invention, but since the semi-reflective and semi-transmissive plates will leak light, the signal-to-noise ratio is not as good as that of the above-mentioned embodiments. Since the wavelength splitting plate sacrifices the bandwidth of the light source, the resolution is not as good as that of the above-mentioned embodiments. The striped reflective and transmissive lenses need to be specially customized, and the cost is not as good as that of the above-mentioned embodiments.

The optical coherence tomography device for synchronous measurement of cornea and retina of the present invention will change the problem of insufficient depth of the existing low-coherence light source OCT measurement method, give full play to the advantages of low-coherence interference technology such as high sensitivity, high resolution, and non-contact, and realize synchronous detection of cornea and retina. Based on the fact that traditional low-coherence OCT can only realize retinal measurement, a set of axial parameter measurement system is designed, and its key technology is studied. Through this system, the axial length and the position information between the interfaces in the eye tissue are obtained. On the basis of extremely low cost, the traditional low-coherence OCT has the ability to synchronously measure the cornea and retina, providing a theoretical basis for the diagnosis and treatment of ophthalmic diseases.

The optical coherence tomography imaging device for synchronous measurement of the cornea and retina of the present invention only needs to add a beam splitter element and a beam combiner element, and can realize imaging of the cornea and retina using a single reference arm, without the need to additionally add dynamic focusing, optical path adjustment mechanisms and multiple reference arms, and finally enters a spectrometer for imaging. The synchronous measurement of the cornea and retina is realized through an optimized optical design, without the need for additional expensive optical elements and electronic equipment, and the cost is low.

The optical coherence tomography imaging device for synchronous measurement of cornea and retina of the present invention synchronously measures cornea and retina, and two paths share a scanning galvanometer. Eye axis parameter information can be obtained by processing data after one measurement.

The optical coherence tomography device for synchronously measuring cornea and retina of the present invention has high speed and can complete the measurement in seconds with one scan of the scanning galvanometer.

The optical coherence tomography device for synchronously measuring the cornea and retina of the present invention has good compatibility and can be applied to any spectral domain OCT and swept source OCT.

Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the protection scope of the invention.

Claims (10)

1. An optical coherence tomography device for synchronous measurement of cornea and retina, characterized in that it comprises: a low-coherence light source, a fiber coupler, a reference arm, a measuring arm and a spectrometer; the light emitted by the low-coherence light source is divided into two paths after passing through the fiber coupler, one of which enters the reference arm and the other enters the measuring arm; the light returned by the reference arm and the measuring arm enters the spectrometer after passing through the fiber coupler; The reference arm includes, in sequence in the direction of the optical path: a reference arm collimating lens, an achromatic glass, a focusing lens and a reference arm reflector; The measuring arm comprises: a cornea branch and a retina branch; The retinal branch includes, 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 includes, in order in the optical path direction: the first lens (L1), the scanning galvanometer, the second lens (L2), the beam splitter, the first reflector (M1), the sixth lens (L6), the seventh lens (L7), the eighth lens (L8), the second reflector (M2), the beam combining element and the fifth lens (L5); wherein the first lens (L1), the scanning galvanometer, the second lens (L2), the beam splitter, 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 tested after passing through the cornea branch and the retina branch, and returns from the cornea branch and the retina branch respectively after reflection; in the retina branch, the scanning galvanometer is conjugate with the pupil of the eye to be tested; in the cornea branch, the scanning galvanometer is conjugate with the fifth lens (L5); The reference light beam reflected by the reference arm reflector and the detection light beam reflected by the interfaces at different depths of the eye to be measured merge in the fiber coupler and are received by the spectrometer. The optical path difference between the reference arm and the measuring arm interferes within a coherence length range of the light source and finally enters the spectrometer for synchronous imaging. 2. The optical coherence tomography device for synchronous measurement of cornea and retina according to claim 1, characterized in that the optical path difference between the two paths of light in the measuring arm in the air is between 0.5 mm and 2 mm. 3. The optical coherence tomography imaging device for synchronous measurement of cornea and retina according to claim 1, characterized in that the beam splitting element and the beam combining element are respectively: a reflector or a semi-reflective and semi-transparent element; If it is a reflector, the light is incident on the reflector at one scanning moment and reflected into the cornea branch, and at another scanning moment it deviates from the reflector and is transmitted into the retina branch; if it is a semi-reflective and semi-transparent element, the emitted light enters the cornea branch, and the transmitted light enters the retina branch. 4. The optical coherence tomography device for synchronous measurement of cornea and retina according to claim 3 is characterized in that the beam splitting element and/or the beam combining element is: a D-type reflector, a striped reflective and transmissive lens with alternating reflective and transmissive surfaces, a semi-reflective and semi-transmissive plate or a wave splitting plate. 5. The optical coherence tomography device for synchronous measurement of cornea and retina according to claim 1, characterized in that the low-coherence light source is a supercontinuum light emitting diode light source with a wavelength range of 800-1100 nm. 6. The optical coherence tomography device for synchronous measurement of cornea and retina according to claim 1, characterized in that the light path length between the beam splitting element and the first reflector (M1) is C1, and the light path length between the beam combining element and the second reflector (M2) is C2, then: the sum of C1 and C2 is equivalent to the axial length of the eye to be measured. 7. The optical coherence tomography device for synchronous measurement of cornea and retina 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 double-cemented lenses with a diameter less than 12.7 mm respectively. 8. The optical coherence tomography device for synchronous measurement of cornea and retina according to claim 1, characterized in that 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). 9. The optical coherence tomography imaging device for synchronous measurement of cornea and retina according to claim 1 is characterized in that the scanning step length of the scanning galvanometer in the X direction satisfies half of the lateral resolution, and the scanning step length in the Y direction satisfies that each step is equal to the diameter of the cornea branch light beam on the beam combining element. 10. The optical coherence tomography device for synchronous measurement of cornea and retina according to any one of claims 1 to 9, characterized in that the spectrometer is used to obtain the distance between the interference signal peaks of the cornea, anterior chamber, lens and retina of the eye to be measured through the synchronously collected interference images, so as to obtain the axial length parameters of the eye.