CN118078206A - Scanning type fundus defocus distribution interferometry device and measurement method - Google Patents

Abstract

The invention relates to a scanning type fundus defocus distribution interferometry device and a scanning type fundus defocus distribution interferometry method, relates to the technical field of optical imaging, and solves the technical problems that peripheral diopter measurement is slow, operation is complex, data processing amount is large, and absolute measurement of fundus defocus distribution cannot be achieved. The measuring device includes: low coherence light source, fiber coupler, reference arm, measurement arm, and OCT detector. The scanning type fundus defocus distribution interferometry device has low cost and simple structure, does not need to collect a plurality of images by staring at multiple angles along with a sighting target by eyes, does not need to add a dynamic focusing and additional adjusting mechanism, can realize absolute measurement of fundus defocus distribution by replacing or adding a dispersion element and a reference surface in a traditional OCT system, and can reconstruct the existing standard OCT instrument with extremely low cost.

Description

Scanning fundus defocus distribution interferometric measurement device and measurement method

Technical Field

The present invention relates to the field of optical imaging technology, and in particular to a scanning fundus defocus distribution interference measurement device and a measurement method.

Background technique

The process of checking the refractive state of the human eye in clinical practice is referred to as optometry. According to different measurement methods, it is further divided into subjective optometry and objective optometry. Among them, subjective optometry refers to obtaining the final measurement result of the refractive state of the eye based on the visual perception of the examinee; while objective optometry directly measures the refractive state of the eye through instruments or retinoscopy technology. Objective optometry includes retinal retinoscopy and computer automatic optometry. The detection process of objective optometry is relatively fast, simple and efficient, but it is impossible to know the subjective perception of human vision. Therefore, in daily work, subjective optometry is often combined with objective optometry results, and finally the fitting result is determined by the human eye's own perception. Usually, the mainstream optometry instruments in clinical practice use high-definition zoom cameras to directly image the retina of the simulated eye. If the refractive error of the simulated eye is x, then only the incident light with a focal power of x can be accurately focused on the retina of the simulated eye. According to the principle of reversibility of the optical path, the focal power of the outgoing light emitted from the retina of the simulated eye is also x. The imaging system needs to be focused to x-light to clearly image the retina of the eye. However, the computer ophthalmometers commonly used in the market can only obtain refractive information in the macular area, but not in the peripheral retinal area. The peripheral defocus theory is considered to be one of the mechanisms of myopia progression. At present, a large number of studies have shown that the peripheral visual signals of the retina play an important role in the emmetropization process of the eyeball and may be an important factor affecting the occurrence of myopia. Early animal experimental evidence found that applying negative lenses to monkey eyes to induce hyperopic defocus stimulation can cause monkeys to develop myopia, and applying positive lenses to induce myopic defocus stimulation can cause monkeys to develop hyperopia. Optical interventions based on the defocus theory, such as multifocal soft lenses and orthokeratology lenses, have been proven to successfully delay axial growth of 30% to 55%. However, the exact relationship between peripheral refraction and eyeball development has not yet been clarified. One of the reasons may be the errors and limitations of peripheral refractive measurement technology of the human eye.

The refractive distribution map of the peripheral and central fields of view is called the defocus distribution topography. At present, there are three main schemes for peripheral refractive power measurement. The first is to achieve peripheral measurement through multi-point gaze of the human eye, and use a Hartmann detector or a fundus camera or a galvanometer scan to obtain the peripheral refractive power; its main problems are slow speed and poor accuracy, and it requires the human eye to gaze at multiple angles for multiple measurements. The second scheme is to realize a large-field fundus camera through optical design, combined with image restoration algorithms such as light field cameras. This scheme is currently less used, mainly because the dynamic range of image restoration is small and the accuracy needs to be verified. The third scheme is a fundus camera with a conventional field of view combined with a galvanometer scan and a zoom lens. The defocus amount is measured by changing the focal length, similar to the zoom lens of a SLR camera, and automatic focus. This scheme system is more complex, and the amount of fundus defocus is directly related to the zoom capability of the zoom lens. The first method is widely used, such as the "window-type" computer ophthalmometer Grand Seiko WAM5500. By asking the patient to rotate the eyeball or head to a certain angle to expose the peripheral retina, the ophthalmometer performs optometry from the front to obtain the peripheral retinal refraction at different gaze angles. However, this measurement method takes a long time to measure, the process is complicated, there are fewer measurement data points, and it cannot reflect the refractive state of the entire retina. In 2020, the domestically designed multispectral refractive topography (MRT, Shengda Tongze, Shenzhen, China) was developed and launched. Compared with the "window-type" ophthalmometer, it does not require the subject's gaze head position or eye position to be changed. It mainly uses single-light rays of different wavelengths to collect fundus images in sequence, and through a deeply developed computer algorithm, the multispectral images after lens compensation are compared and analyzed, and the actual refractive values of each pixel are calculated and summarized to draw the corresponding topography. This method is different from the traditional method. Its advantage is that the measurement is accurate and is not affected by eye muscle contraction and adjustment changes. However, MRT requires a specially customized multi-spectral light source with consistent intensity in each band and a relatively complex alignment and focusing device system. In addition, multiple exposures are required to collect multiple images and obtain a defocus map through an algorithm, which requires a lot of calculations.

Optical coherence tomography (OCT) is a highly promising biomedical optical imaging technology with the advantages of being non-invasive, non-destructive, non-ionizing, high-resolution, and high-sensitivity. It can achieve cross-sectional and three-dimensional imaging of living biological tissues. OCT can achieve an imaging depth of mm and a spatial resolution of μm, and the lateral resolution and longitudinal resolution are independent of each other. Therefore, once the technology came out, it became a hot spot in ophthalmic imaging research and has been widely used in various fields of ophthalmology, providing valuable cytological and histological information for the diagnosis and treatment of diseases. The imaging mode of OCT is scanning imaging, and the light source is a broadband light source. Because it is a broadband light source, each scanning point obtains one-dimensional information in the depth direction, and the scanning array is obtained by two-dimensional scanning of the galvanometer to obtain a three-dimensional image. Usually, the optical design of the measurement arm of OCT requires that the dispersion of the system be controlled to a minimum to ensure that the imaging quality in the depth direction is good.

Summary of the invention

The present invention aims to solve the technical problem that peripheral refractive power measurement in the prior art cannot achieve absolute measurement of fundus defocus distribution, and provides a scanning fundus defocus distribution interference measurement device and measurement method.

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

A scanning fundus defocus distribution interferometric measurement device, comprising: a low coherence light source, a fiber coupler, a reference arm, a measuring arm and an OCT detector; light emitted by the low coherence light source is coupled by the fiber coupler and enters the reference arm and the measuring arm respectively; light returned by the reference arm and the measuring arm is coupled by the fiber coupler and enters the OCT detector;

The reference arm includes: a reference arm collimating lens, achromatic glass, focusing lens and reflector in sequence in the direction of the optical path; the reference arm also includes: an optical path adjustment mechanism, a sight mark and a pupil camera;

The measuring arm includes, in sequence in the direction of the optical path: a measuring arm collimating lens, a scanning galvanometer, and a conjugate lens group; after the light is collimated by the measuring arm collimating lens, it is reflected by the scanning galvanometer and then incident on the eye through the conjugate lens group;

A first wave splitter is also provided between the measuring arm collimating lens and the scanning galvanometer, and the first wave splitter is used to reflect a portion of the light to the optical path adjustment mechanism, and then reflect it back through the reference surface; the optical path adjustment mechanism is used to adjust the position of the reference surface;

A second wave splitter is also provided between the scanning galvanometer and the conjugate lens group, and the second wave splitter is used to reflect a part of the light emitted by the sight mark to the eye through the conjugate lens group;

A middle hole reflector is also provided at the focal position in the middle of the conjugate lens group, and the middle hole reflector is used to reflect the light returned from the fundus into the pupil camera;

The light returned from the reference surface and the fundus interferes with the light returned from the reflector on the reference arm, respectively, and is imaged synchronously in the OCT detector, thereby obtaining absolute information on fundus defocus distribution.

In the above technical solution, the OCT detector is a spectrometer or a balanced detector.

In the above technical solution, the scanning rate is: 100KHz to 10MHz.

In the above technical solution, the lateral resolution is less than 10 μm; and the axial resolution is less than 5 μm.

A measurement method of the above-mentioned scanning fundus defocus distribution interferometry device comprises the following steps:

The fundus image of the current human eye to be tested is captured by scanning galvanometer, and each scanning point has one-dimensional information in the depth direction, and a three-dimensional image of the fundus is obtained at one time through horizontal two-dimensional scanning;

The spectrum of each scanning point is filtered and divided into N bands, where N is a positive integer. Fourier transform is performed on each band to obtain a clarity sequence in the depth direction, and different bands correspond to different depth positions.

A reference surface is set in the measuring arm. The reference surface is dynamically adjusted through the optical path adjustment mechanism to find the absolute defocus amount at the fovea. The return light from the reference surface and the fundus interferes with the return light from the reference arm respectively and is imaged synchronously in the OCT detector to obtain the absolute information of the fundus defocus distribution.

The present invention has the following beneficial effects:

The scanning fundus defocus distribution interference measurement device of the present invention has low cost and simple structure: there is no need for the eyes to follow the sight mark to gaze at multiple angles to collect multiple images, no dynamic focusing and additional adjustment mechanism are added, and only the dispersion element and a reference surface need to be replaced or added to the traditional OCT system to achieve absolute measurement of the fundus defocus distribution.

The scanning fundus defocus distribution interference measurement device of the present invention has high sensitivity: the fundus scattered photons interfere with the reference and then undergo Fourier transform imaging, and the interference imaging method has the advantage of high sensitivity compared with fundus cameras and other methods.

The scanning fundus defocus distribution interference measurement device of the present invention has high contrast: since the interference signal finally enters the single-mode optical fiber, the single-mode optical fiber filters most of the stray light and background light like a small hole. At the same time, the optical fiber end face and the focal plane are conjugated, combined with laser scanning confocal technology, it has the advantage of high contrast.

The scanning fundus defocus distribution interference measurement device of the present invention has high resolution: the lateral resolution of the measurement method based on the OCT structure is related to the pupil size of the eye, and can usually reach 10μm; the axial resolution is related to the bandwidth, and can usually reach 5μm. Therefore, the resolution of this solution is higher than that of traditional fundus cameras and has three-dimensional imaging capabilities.

The scanning fundus defocus distribution interference measurement device of the present invention has high compatibility: on the basis of existing mature OCT products, only one lens needs to be replaced or a dispersion element needs to be inserted, and the software algorithm needs to be updated to realize the fundus defocus distribution measurement capability. By transforming existing mature products, it has high compatibility and scalability.

The scanning fundus defocus distribution interference measurement device of the present invention has high speed: through the scanning imaging method, the scanning speed can reach hundreds of kHz or even MHz, and the three-dimensional image acquisition process can be completed in 1 to 5 seconds. The specific acquisition time depends on the product of the number of scanning points and the scanning speed.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG1 is a schematic diagram showing the principle of a scanning fundus defocus distribution interferometry device.

FIG. 2 is a schematic diagram of the data processing flow of the scanning fundus defocus distribution interferometry measurement device.

FIG3 is a schematic diagram of the structure of a scanning fundus defocus distribution interferometry device.

FIG4 is a schematic diagram of a bandpass filter for a spectral signal (taking 5 as an example).

Figure 5 is a schematic diagram of the optical path of the measuring arm.

Figure 6 is a schematic diagram of the defocus dispersion range of the measurement arm. The design result in the figure is 1.47mm (focal shift of 50nm bandwidth = 1.47mm).

FIG. 7 is a schematic diagram of fundus images of five narrow bands after spectral filtering.

FIG8 is a schematic diagram showing the comparison results of the point spread function describing the clarity of five narrow-band fundus images.

FIG. 9 is a schematic diagram of a fundus defocus distribution map.

Detailed ways

The inventive concept of the present invention is:

The scanning fundus defocus distribution interference measurement device of the present invention has a system composition and working principle that are basically consistent with OCT, but the dispersion of the system measurement arm is maximized in optical design, and the fundus defocus is measured by using the OCT broadband light source and the dispersion in the depth direction, so that different wavelengths are focused at different depths of the fundus, and fundus images of different bands are obtained through data processing algorithms. The brightest band in the fundus scanning area corresponds to the defocus amount of the area. At the same time, a reference surface is added to the measurement arm, and the fundus defocus amount is compared with the reference surface to obtain the actual fundus diopter. Since the scanning field of view of OCT can reach more than 60°, the defocus distribution map of the entire fundus can be obtained by dividing the entire scanning area and calculating the diopter of each divided area.

The device of the present invention will change the design concept of the traditional OCT measuring arm, with the maximization of the dispersion of the measuring arm as the design goal, so that different wavelengths of broadband light can be focused on different depths of the fundus, and the depth range is higher than 1mm to meet the needs of general fundus defocus measurement. When the measurement range is exceeded, the fundus defocus amount is brought into the measurement range by adding a compensation mirror. Its imaging process is consistent with that of traditional OCT, and a lateral two-dimensional scanning with a field of view greater than 60° is achieved through a scanning galvanometer. The collected spectral information is processed by an OCT detector (spectrometer or balanced detector) to obtain a fundus defocus map. The device measures interference signals and has the advantages of high precision, high sensitivity, high contrast, and high speed compared to other defocus map measurement methods. The existing OCT system can be modified at a very low cost to enable it to have the ability to measure fundus defocus distribution, providing a powerful tool for myopia prevention and control and the detection and treatment of various fundus diseases.

The present invention intends to optimize the design of optical elements in the OCT measuring arm based on the traditional standard OCT imaging technology, so that the light of different bands in the broadband light source is focused at different depths of the fundus. In order to meet the requirements of the dynamic range of fundus defocus, the depth direction focusing range is usually designed to be above 1mm. The implementation methods include replacing the material of the optical lens in the measuring arm, inserting a metasurface optical element, inserting a dispersive optical glass or increasing the bandwidth of the broadband light source. The system structure is shown in Figures 1 and 3. Its imaging process is consistent with that of traditional OCT, and a lateral two-dimensional scanning with a field of view greater than 60° is achieved by a scanning galvanometer. In order to meet the application requirements of the human eye, it is also necessary to design a pupil camera, a gaze target and an aperture in the optical path. The collected spectral information is processed by an OCT detector (spectrometer or balanced detector), and the processing process includes: reading spectral data, removing DC terms, spectral windowing and filtering, resampling, i.e., conversion from wavelength to wavenumber space, sub-band dispersion compensation, sub-band Fourier transform processing, calculating the clarity of different bands, and generating a defocus distribution map. The most critical process is spectral window filtering, which divides the spectrum of each scanning point into K bands, each band corresponds to a depth position, and Fourier transforms each sub-band to obtain a two-dimensional image of the band. The two-dimensional fundus scanning area is divided into M×M parts, each of which corresponds to K depth positions. The signal intensity of the images of different bands in the area is compared. The strongest band is the focus of the fundus area, and the depth position corresponding to the band is the defocus amount of the area. Finally, the relative defocus distribution map of the entire fundus can be obtained. At the same time, a reference surface is added to the measurement arm, which interferes with the reference arm of the OCT. At this time, the reference surface image and the fundus image will appear simultaneously in the same OCT detector. The optical path length of the reference surface branch is consistent with the optical path length of the fundus measurement arm. The optical path is adjusted by the electric mechanism to find the absolute value of the defocus amount in the central area of the fundus. The fundus defocus amount is compared with the absolute defocus amount of the reference surface to obtain the actual absolute defocus amount distribution of the fundus. The entire data processing flow is shown in Figure 2, which is divided into three parts. The red dotted box is the data acquisition process; the black dotted box is the spectrum processing process; and the orange dotted box is the defocus amount calculation process. Finally, the feasibility of the device and its advantages in imaging speed, resolution, contrast, and sensitivity were verified through experiments.

The scanning fundus defocus distribution interferometric measurement device of the present invention comprises: a low-coherence light source, a fiber coupler, a reference arm, a measuring arm and an OCT detector; light emitted by the low-coherence light source is coupled by the fiber coupler and enters the reference arm and the measuring arm respectively; light returned by the reference arm and the measuring arm is coupled by the fiber coupler and enters the OCT detector;

The reference arm includes: a reference arm collimating lens, achromatic glass, focusing lens and reflecting mirror in the direction of the optical path; the reference arm also includes: an optical path adjustment mechanism, a sight mark and a pupil camera;

The measuring arm includes, in the direction of the optical path, a measuring arm collimating lens, a scanning galvanometer, and a conjugate lens group. After the light is collimated by the measuring arm collimating lens, it is reflected by the scanning galvanometer and then incident on the eye through the conjugate lens group.

A first wave splitting plate is also provided between the measuring arm collimating lens and the scanning galvanometer, and the first wave splitting plate is used to reflect a part of the light to the optical path adjustment mechanism;

A second wave splitter is also provided between the scanning galvanometer and the conjugate lens group, and the second wave splitter is used to reflect a part of the light emitted by the sight mark to the eye through the conjugate lens group;

A central aperture reflector is also provided at the focal position in the middle of the conjugate lens group, and the central aperture reflector is used to reflect the light emitted by the eye into the pupil camera.

The measuring method of the scanning fundus defocus distribution interferometric measuring device of the present invention comprises the following steps:

The fundus image of the current human eye to be tested is captured by scanning galvanometer, and each scanning point has one-dimensional information in the depth direction, and a three-dimensional image of the fundus is obtained at one time through horizontal two-dimensional scanning;

The spectrum of each scanning point is filtered and divided into N bands, where N is a positive integer. Fourier transform is performed on each band to obtain a clarity sequence in the depth direction, and different bands correspond to different depth positions.

A reference surface is set in the measuring arm. The reference surface can be dynamically adjusted through the optical path adjustment mechanism to find the absolute defocus amount at the fovea. The return light from the reference surface and the fundus interferes with the return light from the reference arm respectively and is imaged synchronously in the OCT detector to obtain the absolute information of the fundus defocus distribution.

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

1. System composition

The present invention is based on ophthalmic applications and proposes a scanning fundus defocus distribution interferometric measurement device. The structure and optical parameters of the Michelson interferometer are determined. The system consists of a light source, a fiber coupler, a measuring arm, a reference arm and an OCT detector, wherein the light source is a low-coherence broadband light source; the reference arm includes a collimating lens, an achromatic fused quartz glass, a focusing lens and a reflector; the OCT detector can be a spectrometer or a balanced detector; the core part is the design of the measuring arm, including a collimating lens, a scanning galvanometer, a beam splitter, a sight mark, a pupil camera, a middle hole reflector, a reference surface reflector, an optical path adjustment mechanism and a conjugate lens group. The core idea of the system design is to maximize the dispersion of the measuring arm so that different wavelengths of the broadband light source are focused at different depths of the fundus. Its core parameters include the wavelength bandwidth of the light source and the dispersion range in the depth direction. The fundus image of the current human eye to be measured is captured by scanning the scanning galvanometer, and each scanning point has one-dimensional information in the depth direction. The three-dimensional image of the fundus is obtained at one time through the horizontal two-dimensional scanning. The spectrum of each scanning point is filtered and divided into N bands. Each band is Fourier transformed to obtain the clarity sequence in the depth direction. Different bands correspond to different depth positions, so the position corresponding to the clearest band is the focus of that position, so as to obtain the relative information of the defocus distribution corresponding to the fundus image. A reference surface is set in the measurement arm, and the reference surface can be dynamically adjusted through the optical path adjustment mechanism to find the absolute defocus amount at the fovea. The return light of the reference surface and the fundus interferes with the same reference arm, and is synchronously imaged in the OCT detector to obtain the absolute information of the fundus defocus distribution.

2. System Working Principle

The essence of this measuring device is a low-coherence detector based on a Michelson interferometer, which uses a (low-coherence) broadband light source and rapid scanning to obtain interference information. The light emitted from the light source enters the measuring arm and the reference arm after being split. The reference light entering the reference arm is reflected by the reflector and returns to the original path, and a reference delay is introduced. The detection light entering the measuring arm is focused into the sample, and then returns to the original path after being scattered and reflected by the sample, and interferes with the reference light. The time delay of the reflection signals in the two arms is related to the structural information inside the sample, and will modulate the interference spectrum. The collected interference signal can be reconstructed by Fourier transform to obtain the reflectivity envelope with depth resolution in the focusing direction of the detection light. Taking one of the paths 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 sample arm and the end face of the 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 spectrum 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 sample 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.

;

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 cause the detection depth of the system to be reduced by half.

3. Data Collection and Processing Methods

The data is acquired and processed by our 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 5 MS/s per channel using a data acquisition board with 12-bit resolution. The sampled data is continuously transferred to the computer memory, and the collected images are saved for 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 NI DAQ and then sent to the driver of the two-dimensional galvanometer. There are M×M transverse scanning points and N longitudinal spectral collection points, so the obtained three-dimensional image is an M×M×N matrix. The first step in the data processing process is to segment the N spectral information of each scanning point. Taking K bands as an example, the spectrum is multiplied with the spectral bandpass filter shown in Figure 4 (taking 5 segments as an example), and K narrow band spectral signals can be obtained. The filtered spectral points are discrete Fourier transformed to generate K depth position information in the axial depth direction. At this time, K M×M×(N/K) three-dimensional matrices are obtained. The average or maximum value of these K three-dimensional matrices along the depth direction can obtain K two-dimensional matrices, that is, K fundus images, which are fundus images of different bands. The method for calculating the clarity is to obtain the point spread function by Fourier transform of the fundus image, and the maximum value of the clarity is the fundus focus position.

IV. Experimental Verification

1. Construction of fundus defocus distribution interferometry device

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, with a bandwidth of 50nm and a central wavelength of 850nm. The fiber coupler, lens, and reflector are all Thorlabs products. The galvanometer is Thorlabs' GVS002 two-dimensional galvanometer, the driving voltage card is NI's NI6221, the line array camera is e2v's high-speed line array camera E2V-Octoplus-2K-W4/EV71YEM4CL2014-BA9, and the grating is Wasatch Photonics' WP-HD1800/840. In order to achieve axial dispersion, this verification only replaced the collimating lens with the Edmud plano-convex lens, model 48647. Based on the selection of the above devices, Zemax was used for optimization, and the parameters of the lens in the sample arm and the spectrometer were designed to meet the axial dispersion of the fundus to reach 1.47 mm, as shown in Figure 6, and to meet the imaging requirements of the defocus measurement. The design results of the measurement arm are shown in Figure 5.

In order to prove the feasibility of the device of the present invention, a group of fundus images were measured by the above device, and the defocus distribution results of the fundus were obtained according to the above data processing process, as shown in Figure 7 which is a fundus image of 5 bands, Figure 8 which is a clarity comparison result of the fundus images of 5 bands, and Figure 9 which is the defocus distribution map after processing.

It can be seen that the device of the present invention can expand the depth range of the fundus focused light spot and improve the resolution, sensitivity, contrast and speed performance of other fundus peripheral defocus measurement methods at a low cost by replacing only one collimating lens. This solution transforms mature OCT products to enable them to have the ability to measure fundus defocus distribution.

The scanning fundus defocus distribution interference measurement device of the present invention has low cost and simple structure: there is no need for the eyes to follow the sight mark to gaze at multiple angles to collect multiple images, no dynamic focusing and additional adjustment mechanism are added, and only the dispersion element and a reference surface need to be replaced or added to the traditional OCT system to achieve absolute measurement of the fundus defocus distribution.

The scanning fundus defocus distribution interference measurement device of the present invention has high sensitivity: the fundus scattered photons interfere with the reference and then undergo Fourier transform imaging, and the interference imaging method has the advantage of high sensitivity compared with fundus cameras and other methods.

The scanning fundus defocus distribution interference measurement device of the present invention has high contrast: since the interference signal finally enters the single-mode optical fiber, the single-mode optical fiber filters most of the stray light and background light like a small hole. At the same time, the optical fiber end face and the focal plane are conjugated, combined with laser scanning confocal technology, it has the advantage of high contrast.

The scanning fundus defocus distribution interference measurement device of the present invention has high resolution: the lateral resolution of the measurement method based on the OCT structure is related to the pupil size of the eye, and can usually reach 10μm; the axial resolution is related to the bandwidth, and can usually reach 5μm. Therefore, the resolution of this solution is higher than that of traditional fundus cameras and has three-dimensional imaging capabilities.

The scanning fundus defocus distribution interference measurement device of the present invention has high compatibility: on the basis of existing mature OCT products, only one lens needs to be replaced or a dispersion element needs to be inserted, and the software algorithm needs to be updated to realize the fundus defocus distribution measurement capability. By transforming existing mature products, it has high compatibility and scalability.

The scanning fundus defocus distribution interference measurement device of the present invention has high speed: through the scanning imaging method, the scanning speed can reach hundreds of kHz or even MHz, and the three-dimensional image acquisition process can be completed in 1 to 5 seconds. The specific acquisition time depends on the product of the number of scanning points and the scanning speed.

Obviously, the above embodiments are merely examples for 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 (5)

1. A scanning fundus defocus distribution interferometry device, characterized in that it comprises: a low coherence light source, a fiber coupler, a reference arm, a measuring arm and an OCT detector; the light emitted by the low coherence light source is coupled by the fiber coupler and then enters the reference arm and the measuring arm respectively; the light returned by the reference arm and the measuring arm is coupled by the fiber coupler and then enters the OCT detector; The reference arm includes: a reference arm collimating lens, achromatic glass, focusing lens and reflector in sequence in the direction of the optical path; the reference arm also includes: an optical path adjustment mechanism, a sight mark and a pupil camera; The measuring arm includes, in sequence in the direction of the optical path: a measuring arm collimating lens, a scanning galvanometer, and a conjugate lens group; after the light is collimated by the measuring arm collimating lens, it is reflected by the scanning galvanometer and then incident on the eye through the conjugate lens group; A first wave splitter is also provided between the measuring arm collimating lens and the scanning galvanometer, and the first wave splitter is used to reflect a portion of the light to the optical path adjustment mechanism, and then reflect it back through the reference surface; the optical path adjustment mechanism is used to adjust the position of the reference surface; A second wave splitter is also provided between the scanning galvanometer and the conjugate lens group, and the second wave splitter is used to reflect a part of the light emitted by the sight mark to the eye through the conjugate lens group; A middle hole reflector is also provided at the focal position in the middle of the conjugate lens group, and the middle hole reflector is used to reflect the light returned from the fundus into the pupil camera; The light returned from the reference surface and the fundus interferes with the light returned from the reflector on the reference arm, respectively, and is imaged synchronously in the OCT detector, thereby obtaining absolute information on fundus defocus distribution. 2. The scanning fundus defocus distribution interferometry measurement device according to claim 1, characterized in that the OCT detector is a spectrometer or a balanced detector. 3. The scanning fundus defocus distribution interferometry measurement device according to claim 1, characterized in that the scanning rate is: 100KHz to 10MHz. 4 . The scanning fundus defocus distribution interferometry device according to claim 1 , wherein the lateral resolution is less than 10 μm and the axial resolution is less than 5 μm. 5. A method for measuring the scanning fundus defocus distribution interferometry device according to claim 1, characterized in that it comprises the following steps: The fundus image of the current human eye to be tested is captured by scanning galvanometer, and each scanning point has one-dimensional information in the depth direction, and a three-dimensional image of the fundus is obtained at one time through horizontal two-dimensional scanning; The spectrum of each scanning point is filtered and divided into N bands, where N is a positive integer. Fourier transform is performed on each band to obtain a clarity sequence in the depth direction, and different bands correspond to different depth positions. A reference surface is set in the measuring arm. The reference surface is dynamically adjusted through the optical path adjustment mechanism to find the absolute defocus amount at the fovea. The return light from the reference surface and the fundus interferes with the return light from the reference arm respectively and is imaged synchronously in the OCT detector to obtain the absolute information of the fundus defocus distribution.