CN114431823A - Time domain OCT eye axis length measurement system based on imaging spectrometer - Google Patents

Time domain OCT eye axis length measurement system based on imaging spectrometer Download PDF

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Publication number
CN114431823A
CN114431823A CN202210090936.2A CN202210090936A CN114431823A CN 114431823 A CN114431823 A CN 114431823A CN 202210090936 A CN202210090936 A CN 202210090936A CN 114431823 A CN114431823 A CN 114431823A
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light
original
collimator
delay line
optical
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吴南寿
岑颖珊
李泽
张章
杨旭伦
何镇楠
刘永安
黄鸿衡
黄铭斌
张�浩
胡积烨
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Foshan Linguistic Technology Co ltd
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/102—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for optical coherence tomography [OCT]
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/0016—Operational features thereof
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/1005—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for measuring distances inside the eye, e.g. thickness of the cornea
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/14—Arrangements specially adapted for eye photography

Abstract

The invention provides a time domain OCT eye axis length measuring system based on an imaging spectrometer, which comprises: a light source for emitting original light; the optical fiber coupler is used for receiving original light and dividing the original light into first original light and second original light; a reference arm, comprising: the first original light sequentially passes through the first collimator, the optical delay line device and the first focusing lens, and after being reflected by the single-sided reflector, the original path returns to obtain reference light which enters the optical fiber coupler; the sample arm is used for receiving the second original light, entering the human eyes, returning from the original path of the human eyes to obtain sample light, and entering the optical fiber coupler; a second collimator; and the reference light and the sample light enter the spectrometer through the second collimator after interfering in the optical fiber coupler. The invention can ensure the accuracy of the eye axis measurement.

Description

Time domain OCT eye axis length measurement system based on imaging spectrometer
Technical Field
The invention belongs to the technical field of eye axis length measurement, and particularly relates to a time domain OCT eye axis length measurement system based on an imaging spectrometer.
Background
With the widespread use of electronic products in various age groups, eye health problems become more prominent, and myopia and strabismus are the main manifestations of teenagers. Eyes are the window of soul, and the eye health is vital to the physical and mental health of people.
Among the optical biological parameters of the eye, Axial Length (AL) can be an important parameter for monitoring myopia of the eyeball. At present, partial optical instruments aiming at the eye axis measurement exist in the market, various optical biological measuring instruments are widely applied to clinic, and mainly adopted measuring technologies comprise a partial optical coherence based optical coherence, such as Carl Zeiss IOLMmaster 500 and Nidek AL-Scan; optically low coherence interference, such as Topcon Aladdin, Tomey CASIA SS-1000, Tomey CASIA 2.
The imaging technology based on partial optical coherence is an imaging technology using frequency domain optical coherence tomography (SD-OCT), and is used for respectively imaging and splicing the anterior segment and the posterior segment of the eye to obtain a full-eye tomographic image, and then obtaining the axial length of the eye according to pixel points and resolution; the optical low coherence interference is to use time domain optical coherence tomography (TD-OCT), use a photoelectric balance detector to acquire interference signals, and obtain the actual length of the eye axis according to the corresponding relation between time and the interference signals.
Frequency-domain optical coherence tomography and time-domain optical coherence tomography differ in the system by the apparatus that receives the spectral signal. The SD-OCT can simultaneously acquire interference signals for an area with a certain depth range, but the imaging depth is controlled by the bandwidth of a broadband light source, only a single part can be imaged, and if the detection part is changed, the optical path and a focusing lens need to be adjusted, so that the experimental efficiency is influenced; the TD-OCT is to spend time to reach the effect of changing the optical path by moving the reference mirror, and the equipment for receiving the interference spectrum signal is a photoelectric balance detector, and can receive other interference noise on the optical path of the sample at the same time, which affects the measuring accuracy of the eye axis.
Disclosure of Invention
In order to overcome the technical defects, the invention provides a time domain OCT eye axis length measuring system based on an imaging spectrometer.
In order to solve the problems, the invention is realized according to the following technical scheme:
a time domain OCT eye axis length measurement system based on an imaging spectrometer, comprising:
a light source for emitting original light;
the optical fiber coupler is used for receiving original light and dividing the original light into first original light and second original light;
a reference arm, comprising: the first original light sequentially passes through the first collimator, the optical delay line device and the first focusing lens, and after being reflected by the single-sided reflector, the original path returns to obtain reference light which enters the optical fiber coupler;
the sample arm is used for receiving the second original light, entering the human eyes, returning from the original path of the human eyes to obtain sample light, and entering the optical fiber coupler;
a second collimator;
and the reference light and the sample light enter the spectrometer through the second collimator after interfering in the fiber coupler.
As a further development of the invention, the sample arm comprises: a third collimator and a compensating dispersion element;
the second original light enters the human eyes through the third collimator and the compensating dispersion element in sequence, sample light is obtained after different depths of the human eyes are scanned, and the sample light returns to the optical fiber coupler through the compensating dispersion element and the third collimator.
As a further improvement of the present invention, after passing through the first collimator, the first original light enters the optical delay line device from point a, is refracted to point B at point a, is reflected at both points B and C, is refracted out at point D, and reaches the first focusing lens.
As a further improvement of the invention, the light source is an SLD low coherence light source.
As a further improvement of the present invention, the spectrometer comprises: the transmission grating, the second focusing lens and the linear array CCD camera;
after the reference light and the sample light interfere in the optical fiber coupler, the reference light and the sample light pass through the second collimator, pass through the transmission grating, are divided into a line of light according to wavelength, are focused by the focusing lens, and are vertically incident on corresponding pixel points of the linear array CCD camera.
As a further improvement of the present invention, when the first original light enters the optical delay line device, the relationship between the optical path length scanned by the optical delay line device and the rotation angle is as follows:
Figure BDA0003487857630000021
where S is the optical path length of light in the delay line, a is the side length of the optical delay line device, α is the incident angle of the light, n is the refractive index of the optical delay line device, and β is the refraction angle.
As a further improvement of the invention, the optical delay line device can be a square, transparent prism.
As a further improvement of the present invention, the optical delay line device may change an optical path length by moving the single-sided mirror.
Compared with the prior art, the invention has the following beneficial effects: the invention combines the SD-OCT and TD-OCT imaging systems, analyzes the TD-OCT interference spectrum signal by using a spectrometer for receiving the interference spectrum in the SD-OCT, and then obtains the imaging depth in a large range by simple calculation, thereby obtaining the accurate length of the eye axis.
Drawings
Embodiments of the invention are described in further detail below with reference to the attached drawing figures, wherein:
FIG. 1 is a schematic diagram of the overall structure of a time-domain OCT eye axis length measuring system based on an imaging spectrometer according to the present invention;
FIG. 2 is a diagram of an optical delay line device according to the present invention;
FIG. 3 is a graph showing the results of one-dimensional chromatography using the present invention.
Description of the labeling: 1. a light source; 2. a fiber coupler; 3. a reference arm; 31. a first collimator; 32. an optical delay line device; 33. a first focusing lens; 34. a single-sided mirror; 4. a sample arm; 41. a third collimator; 42. a compensating dispersion element; 5. a second collimator; 6. a spectrometer; 61. a transmission grating; 62. a second focusing lens; 63. linear array CCD camera.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
The invention provides a time domain OCT eye axis length measuring system based on an imaging spectrometer 6, as shown in figure 1, comprising: the device comprises a light source 1, a fiber coupler 2, a reference arm 3, a sample arm 4, a second collimator 5 and a spectrometer 6; the light source 1 is used for emitting original light; the optical fiber coupler 2 is used for receiving original light and dividing the original light into first original light and second original light; the reference arm 3 includes: the first original light sequentially passes through the first collimator 31, the optical delay line device 32 and the first focusing lens 33, the first original light is reflected by the single-sided reflector 34, and then returns to the original path to obtain reference light, and the reference light enters the optical fiber coupler 2; the sample arm 4 is used for receiving the second original light, entering the human eye, returning from the original path of the human eye to obtain sample light, and entering the optical fiber coupler 2; after the reference light and the sample light interfere in the fiber coupler 2, they enter the spectrometer 6 through the second collimator 5.
Time-domain optical low coherence interferometry (TD-OCT) is based on the Michelson interference principle to perform imaging, and the working process is as follows: light emitted by the light source 1 is divided into two beams after passing through a beam splitter obliquely arranged at 45 degrees, the two beams enter the sample arm 4 and the reference arm 3 respectively, return along the original path after being reflected, meet at the beam splitter finally to generate interference and are received by a detector, and therefore the internal information of the sample at the depth is obtained.
The normal human eyeball axis is 24 mm long. In order to quickly realize long-range measurement, the invention firstly changes on an experimental system of the TD-OCT, a rotary optical delay line device is introduced from a reference arm, as shown in figure 2, first original light enters the optical delay line device from a point A after passing through a first collimator, is refracted to a point B at the point A, is reflected at the points B and C, is refracted out at a point D, and reaches a first focusing lens. The relationship between the optical path length scanned by the optical delay line device and the rotation angle is as follows:
Figure BDA0003487857630000041
where S is the optical path length of light in the delay line, a is the side length of the optical delay line device 32, α is the incident angle of the light, n is the refractive index of the optical delay line device 32, and β is the refraction angle.
Specifically, the sample arm 4 includes: a third collimator 41 and a compensating dispersion element 42; the second original light sequentially passes through the third collimator 41 and the compensation dispersion element 42 and enters the human eye, the human eye is scanned at different depths to obtain sample light, and the sample light returns to the optical fiber coupler 2 through the compensation dispersion element 42 and the third collimator 41.
Introducing an imaging spectrometer 6 for frequency domain optical coherence tomography (SD-OCT) to the portion receiving the interference spectral signal after ensuring that the scanning optical path of the delay line exceeds the maximum eye axis length of the human eye, the spectrometer 6 comprising: a transmission grating 61, a second focusing lens 62 and a line CCD camera;
after the reference light and the sample light interfere in the optical fiber coupler 2, the reference light and the sample light pass through the second collimator 5, are divided into a line of light according to wavelength by the transmission grating 61, are focused by the focusing lens, and are vertically incident on corresponding pixel points of the linear array CCD camera. The transmission grating 61 analyzes the interference spectrum from the time domain to the frequency domain, divides a beam of interference light into a line of light arranged along the wavelength according to the characteristic of wavelength light splitting, and collects and processes the light by using a linear array CCD camera, so that the fault information in a section of depth range can be obtained.
Preferably, the optical delay line device 32 may be a square prism, a triangular prism, or a transparent prism. In addition, the optical delay line device 32 can change the optical path by moving the single-sided mirror 34.
The invention will be further explained with reference to specific embodiments as follows:
the system adopts an SLD low-coherence light source, and original light from the light source enters an optical fiber coupler along a path of optical fiber to be divided into first original light and second original light which respectively enter a reference arm and a sample arm. The first original light entering the reference arm is collimated in parallel by the collimator and then enters the optical delay line device, the first original light is subjected to multiple refraction and reflection in the optical delay line device, leaves the optical delay line device, vertically enters the focusing lens and is reflected by the single-sided reflector, the reference light is obtained, and the original path returns to the light coupler; the second original light entering the sample arm is collimated in parallel by the collimator and then vertically enters a compensation dispersion element (used for compensating dispersion of light rays caused in the optical delay line device), then the light rays enter human eyes, different depths of the human eyes are scanned, the sample light is obtained by reflection according to the original path, and the sample light returns to the optical fiber coupler. Returning from reference arm and sample arm to two bundles of light that light coupler meets and taking place to interfere, coming out from the optic fibre of connecting the second collimator, through the transmission grating, divide into a list of light according to the wavelength and focus through the focusing lens, on the corresponding pixel point of vertical drive-in linear array CCD camera, the interference spectrum that linear array CCD camera received at this moment is according to the interference information of certain depth range of frequency arrangement, and the laser intensity I of interference spectrum can be expressed as:
Figure BDA0003487857630000051
wherein r is1，r2The reflection coefficients of the reference arm and the sample arm, respectively; a is the amplitude of laser amplitude; k is the wave vector; Δ z is the optical path difference; n is the total number of the optical path differences from one to different, namely the total number of the CCD of the camera; y is the number of different wavelengths of the interference light; x is 1 to y. And different Δ znCorresponding to different In。
Then, for wave vector k in equation (2)xThe spectral information collected in the space, i.e. the linear array camera, is subjected to data processing operations such as fourier transform and the like at the computer end 12, so that light intensity information corresponding to different Δ z can be obtained, and the fault information of a scanned sample at a certain depth can be obtained.
Figure BDA0003487857630000052
Where i is the imaginary unit.
When the optical delay line device 32 does not rotate, the system is equivalent to an SD-OCT, and can carry out the fault detection in a small range at a certain depth. When the optical delay line device 32 starts to rotate, the optical path of the reference arm 3 changes, the isooptic point corresponding to the sample arm 4 also changes, and the detectable depth also changes according to the condition of interference, namely the optical path difference is constant. By using the corneal position as the measurement site and slowly rotating the optical delay line device 32, the process that the fourier map changes with time and an interference peak appears and disappears, namely the process that the corresponding detection depth continuously approaches to the posterior segment of the eye can be observed. A motor feedback signal for driving the optical delay line device 32 to rotate is connected to the linear array camera for exposure triggering to realize the synchronization of optical path change and camera acquisition. At the data processing end, the number of frames of two interference peaks is recorded and processed, and the two interference Fourier spectrums, namely the measured OCT one-dimensional chromatography result of the cornea and the OCT one-dimensional chromatography result of the retina, are combined, so that a result image as shown in figure 3 can be obtained. And (3) recording the position of an interference peak at the front surface of the cornea as a, recording the position of the interference peak on the retina as b, recording the distance between a and b as D1 and the optical path change of the optical path in the rotating optical delay line device 32 as D2 according to the OCT one-dimensional chromatography result by using a peak identification method, wherein the eye axis length D of the eye to be measured meets the condition that D is D1+2 multiplied by D2. Wherein d1 is the actual distance calculated according to the SD-OCT imaging principle, and d2 is obtained by substituting equation (1) according to the recorded time difference of two frames containing interference peaks.
In summary, the optical delay line device 32 is added to the TD-OCT system, so that the effect of changing the optical path of the reference arm 3 in a large range in a short time can be achieved, the basic requirement of measuring the full length of the eye axis is met, the detection speed along the depth range is increased, and the full length of the eye axis is rapidly measured. The imaging spectrometer 6 is used for splitting the time domain interference signal, the time domain is converted into a wave vector domain, one beam of light containing multi-wavelength interference is split according to the frequency, interference peaks caused by other reflecting surfaces can be separated, especially the reflection of the retina layers can come from the retinal pigment epithelium layer and can also come from the nerve fiber layer, and if the interference peaks in the time domain interference spectrum possibly received by the optical electric balance detector form an envelope, the accuracy is influenced. The grating is used for analyzing the interference light to obtain interference peaks of different reflecting surfaces, so that the specific position of strong interference caused by reflection of cornea and retinal epithelial layer can be accurately obtained, the advantage of high resolution of SD-OCT is fully utilized, meanwhile, the noise signal of time domain interference signal is separated from signal noise, the signal to noise ratio of detection signal is improved, and the accuracy of eye axis measurement is ensured.
The present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed.

Claims (8)

1. A time-domain OCT eye axis length measuring system based on an imaging spectrometer is characterized by comprising:
a light source for emitting original light;
the optical fiber coupler is used for receiving original light and dividing the original light into first original light and second original light;
a reference arm, comprising: the first original light sequentially passes through the first collimator, the optical delay line device and the first focusing lens, and after being reflected by the single-sided reflector, the original path returns to obtain reference light which enters the optical fiber coupler;
the sample arm is used for receiving the second original light, entering the human eyes, returning from the original path of the human eyes to obtain sample light, and entering the optical fiber coupler;
a second collimator;
and the reference light and the sample light enter the spectrometer through the second collimator after interfering in the fiber coupler.
2. The time-domain OCT eye-length measurement system of claim 1, wherein the sample arm comprises: a third collimator and a compensating dispersion element;
the second original light enters the human eyes through the third collimator and the compensating dispersion element in sequence, sample light is obtained after different depths of the human eyes are scanned, and the sample light returns to the optical fiber coupler through the compensating dispersion element and the third collimator.
3. The time-domain OCT eye length measurement system of claim 1, wherein the first raw light enters the optical delay line device from point a after passing through the first collimator, is refracted to point B at point a, is reflected at both points B and C, is refracted out at point D, and reaches the first focusing lens.
4. The imaging spectrometer-based time-domain OCT eye axis length measurement of any of claims 1-3, wherein the light source is an SLD low coherence light source.
5. The imaging spectrometer-based time-domain OCT eye axis length measurement of any of claims 1-3, the spectrometer comprising: the transmission grating, the second focusing lens and the linear array CCD camera;
after the reference light and the sample light interfere in the optical fiber coupler, the reference light and the sample light pass through the second collimator, pass through the transmission grating, are divided into a line of light according to wavelength, are focused by the focusing lens, and are vertically incident on corresponding pixel points of the linear array CCD camera.
6. The imaging spectrometer-based time-domain OCT eye axis length measurement of any of claims 1-3, wherein the relationship between the optical path length scanned by the optical delay line device and the rotation angle when the first original light enters the optical delay line device is:
Figure FDA0003487857620000021
where S is the optical path length of light in the delay line, a is the side length of the optical delay line device, α is the incident angle of the light, n is the refractive index of the optical delay line device, and β is the refraction angle.
7. The imaging spectrometer-based time-domain OCT eye-axis length measurement according to claim 1, wherein said optical delay line device can be a square prism, a triangular prism, or a transparent prism.
8. The imaging spectrometer-based time-domain OCT eye-axis length measurement according to claim 1, wherein said optical delay line device can change the optical path by moving said single-sided mirror.
CN202210090936.2A 2022-01-25 2022-01-25 Time domain OCT eye axis length measurement system based on imaging spectrometer Pending CN114431823A (en)

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