CN113995373A

CN113995373A - Optical instrument focusing method based on H-S reconstruction of human eye wavefront aberration

Info

Publication number: CN113995373A
Application number: CN202111185750.7A
Authority: CN
Inventors: 黄铭斌; 张�浩; 胡积烨; 李泽; 张章; 杨旭伦; 何镇楠; 刘永安; 黄鸿衡; 吴南寿
Original assignee: Foshan Linguistic Technology Co ltd
Current assignee: Foshan Linguistic Technology Co ltd
Priority date: 2021-10-12
Filing date: 2021-10-12
Publication date: 2022-02-01

Abstract

The focusing method of the optometry instrument for reconstructing wavefront aberration of human eyes based on H-S comprises the following steps: the method comprises the steps of detecting the wave front by adopting a Hartmann-Shack detection method of optical track tracking, dividing the light wave into sub light waves through a micro-lens array, focusing the sub light waves on a focal plane through a lens to form a light spot array, calculating the offset of each micro-lens in the x and y directions by comparing the wave front with aberration with the light spot array of a reference plane wave formed by mirror reflection, reconstructing wave front aberration by utilizing a Zernike polynomial, calculating the diopter of human eyes after solving the coefficient of the Zernike polynomial, and performing focusing operation of an instrument by using the diopter. The method comprises the steps that the wave front aberration of human eyes is obtained through an H-S sensor, the Zernike polynomial is utilized to expand the wave front and calculate the diopter of the human eyes to realize the rapid and accurate focusing of an optometry instrument on the human eyes, so that the measurement focus of optometry instruments such as an OCT instrument and a biological parameter measuring instrument can be accurately located on the retina; need not to carry out artifical regulation, avoided artificial subjective impression to influence.

Description

Sight instrument focusing method based on H-S reconstruction human eye wavefront aberration

Technical Field

The invention relates to the field of optometry, in particular to an optometer focusing method for reconstructing wavefront aberration of human eyes based on H-S.

Background

The human eyeball is a photoreceptor. The light reflected by the object before the eye is refracted by the cornea and focused by the crystalline lens, so that the light can be accurately focused on the retina for clear imaging. However, if the focusing function of the crystalline lens is in a problem, external light is focused in front of the retina or is focused behind the retina to form an image, so that the scene in front of the eye is blurred, namely, the myopia or the hyperopia is caused.

Human eye visual effects can be described in terms of wavefront aberrations. In the last 60 th century, Smirnov realized the first measurement of human eye aberration, and through the development of half a century, the measurement technology of human eye wavefront aberration has been widely used clinically. The Hartmann Shack theory of tracking (RayTracing) is used most widely. Hartmann-Shack directs a laser beam into the fundus of a human eye, and the light reflected off the retina exits the eye into a Hartmann-Shack (H-S) wavefront sensor. The micro-array lens images on the CCD. If the eyes have no aberration, the emergent light wave is a plane light wave; when the ocular optical system causes aberration, the outgoing light wave is distorted. The light wave is divided into a plurality of wavelets by a micro lens array and focused on a CCD detector by a lens. The offset is calculated by using the position of the spot centroid acquired on the CCD detector relative to the ideal spot, so that the wavefront aberration information of human eyes can be obtained. Finally, the coefficients of Zernike polynomials are calculated by reconstructing the wavefront aberration to obtain the refractive power of the human eye.

By utilizing the refractive power of human eyes, a focusing motor of the optometry instrument can be driven to reach the position where clear images of eyegrounds can be obtained at one time, meanwhile, a focusing target can form the clearest image in the human eyes, and the focusing operation is finished.

The focusing mode of the existing optometry instrument is mainly divided into an automatic focusing mode and a manual focusing mode. The main method of automatic focusing is that the equipment focusing system moves back and forth in a limited range, and the best focusing state set in advance is compared with the acquisition condition obtained in the moving process, so as to find out the best corresponding position for imaging and finish focusing. The method generally automatically finds a better focusing position only in a certain range, and if long-distance focusing condition comparison is carried out, the time is longer, the efficiency is reduced, so that the problem that instrument measurement is carried out without focusing to the clearest state can be caused, and the precision error exists.

The manual focusing is similar to the automatic focusing method, but is limited in that glasses of each operator have differences, subjective judgment of each person on image definition is different, and the risk of inaccurate verification data is caused by manual judgment without focusing auxiliary reference.

The focusing method proposed herein requires accurate placement of the CCD on the plane of focus of the microlens array for better operation. If in a non-focal plane, increases the error in wavefront reconstruction and results in diopter calculation errors. It is important to note that the type of microlens array is also selected, and if the wavelets into which the light is split are not fine enough, the effects of higher order aberrations are easily introduced. In addition, each instrument needs to be corrected once after the production equipment is completed, and the primary correction is to enable the sub-optical wave mass center of the planar optical wave to accurately fall on an ideal position on the CCD detector, so that the subsequent wavefront reconstruction is facilitated. Therefore, in order to implement the focusing method, an additional optical path is required on the instrument, and therefore, the complexity and cost of the optical path structure and assembly are increased.

The focal length position plays a crucial role in determining whether the optometry instrument can perform accurate measurement. However, in the conventional focusing method, the instrument is moved back and forth within a measuring range to find a focus position, and the focus position is adjusted completely according to subjective feeling of a user. For example, in the measurement process of the OCT, the OCT needs to be directed at the eyeball of a person and move the OCT forward and backward, the position of the focus is determined by the brightness of the obtained image, and when the detection light energy falls on the retina, the image is brightest. For another example, when the biological parameter measuring instrument measures the eye axis information, the instrument needs to be moved back and forth to find the position with the strongest interference signal after aligning with the center of the pupil of the eyeball.

Disclosure of Invention

The invention overcomes the defects in the prior art and provides a focusing method of a vision apparatus for reconstructing the wavefront aberration of human eyes based on H-S.

In order to solve the technical problems, the invention is realized by the following technical scheme:

the focusing method of the optometry instrument for reconstructing wavefront aberration of human eyes based on H-S comprises the following steps: the method comprises the steps of detecting the wave front by adopting a Hartmann-Shack detection method of optical track tracking, dividing the light wave into sub light waves through a micro-lens array, focusing the sub light waves on a focal plane through a lens to form a light spot array, calculating the offset of each micro-lens in the x and y directions by comparing the wave front with aberration with the light spot array of a reference plane wave formed by mirror reflection, reconstructing wave front aberration by utilizing a Zernike polynomial, calculating the diopter of human eyes after solving the coefficient of the Zernike polynomial, and performing focusing operation of an instrument by using the diopter.

Furthermore, the Hartmann-Shack detection method for constructing the optical track tracking comprises an incidence module and a reflection module, wherein in the light path of the incidence module, near-infrared laser beams generated by a laser source firstly pass through a transparent turntable to weaken dispersion, come out of the turntable to enter a focusing lens, are focused on a first polarization beam splitter prism, then are reflected to a second polarization beam splitter prism, and then are reflected by the second polarization beam splitter prism to enter the eye fundus of a human eye; the light enters the eye through the cornea, part of the light reflected by the cornea is transmitted to the focusing lens from the second polarization beam splitter prism, enters the micro-array lens through the collimating lens, is converged on the focal plane to form a light spot array after passing through the micro-array lens, and the light spot array image is acquired through the detection of the CCD detector.

Further, the laser light source is an 850nm laser light source.

Further, reconstructing the wavefront aberration to obtain the diopter of the human eye: when an ideal plane wave passes through the micro lens array, the wave front focuses on the focal plane of the micro lens to form a spot array, when the wave front with aberration passes through the micro lens array, the spot array focused on the focal plane can generate deviation, so that the relative offset delta x and delta y of each micro lens in the x and y directions can be calculated by comparing the ideal plane wave with the spot array with the wave front with aberration, a CCD detector is used for obtaining a spot array image, the OSTU threshold segmentation is used for noise suppression and obtaining the centroid position of each spot, then the centroid offset of the spots is determined, the wave front slope can be calculated, a Zernike polynomial is selected as a wave front reconstruction algorithm, the Zernike polynomial coefficient is obtained, the human wavefront aberration can be reconstructed, and the diopter can be calculated.

Further, according to geometric optics, the relative displacement of the spot is proportional to the local slope at that point, so the wavefront slopes in the two orthogonal directions x and y are:

where W (x, y) is the incident wavefront aberration and f is the focal length of the microlens.

Further, the wavefront is represented by a Zernike polynomial:

by substituting formula 3 for formulae 1 and 2, one can obtain:

then order

Writing

equations

6, 7, 8, 9 in the form of a matrix:

in the above matrix, ω_jThe matrix is a coefficient matrix of the reconstructed wavefront, and the above formula is written as β ═ α ω → α by least square solution^Tβ＝α^Tαω→ω＝(α^Tα)^-1α^Tβ＝α⁺β

The wavefront aberration of the human eye can be reconstructed by solving Zernike polynomial coefficients, and the refractive power can be calculated according to the following formula:

wherein R is the pupil radius, C is the cylinder power, S is the sphere power, omega₄、ω₅、ω₆Are Zernike polynomial coefficients.

Further, the instrument is driven to focus by utilizing the diopter of human eyes: according to the position relation between the diopter and the second lens, the motor for driving and adjusting the second lens can quickly adjust the position of the second lens, so that the image can be clear on the retina, and the automatic focusing function is realized.

Compared with the prior art, the invention has the beneficial effects that:

the invention obtains the wave front aberration of human eyes through the H-S sensor, utilizes the Zernike polynomial to expand the wave front and calculates the diopter of the human eyes to realize the rapid and accurate focusing of the optometry instrument to the human eyes, and has the advantages that:

the method has the advantages that: the problem that the image cannot be formed on the retina due to the ametropia of the human eye can be corrected, so that the measurement focus of optical instruments such as an OCT instrument and a biological parameter measuring instrument can be accurately positioned on the retina;

the method has the advantages that: manual adjustment is not needed, so that the influence of artificial subjective feeling is avoided;

the method has the advantages that: compared with the mode of manually adjusting the instrument forwards and backwards and the like, the method can realize quick and accurate adjustment.

Drawings

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, with the understanding that the present disclosure is to be considered as an exemplification of the invention and is not intended to limit the invention to the embodiments illustrated in the drawings, in which:

FIG. 1 is a diagram of an optical path structure of H-S detection method

FIG. 2 is a schematic diagram of a PBS

FIG. 3 is a flow chart of an algorithm for finding eye diopter

FIG. 4 is a schematic view of lens imaging

FIG. 5 is a schematic view of focusing of an optical path

In the figure, the light source is 1-850 nm

2-rotating disk

3-lens

4-first polarization beam splitter prism

5-CCD detector

6-microlens array

7-collimating lens

8-focusing lens

9-a second polarization beam splitter prism;

10-a first lens;

11-second lens, 11.1, 11.2, 11.3 are second lens, but the positions are different;

12-third lens.

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 mainly aims to provide a device and a method for focusing an optometry instrument based on H-S reconstruction of wave aberration of human eyes, and the device mainly comprises: the system comprises an H-S sensor (a micro lens array and a CCD detector), a target module, a control module and a computer processing terminal.

The human eye is not a perfect dioptric system, and various aberrations exist in the cornea and the crystalline lens, and the imaging quality of the human eye is affected by the existence of the aberrations. Therefore, the diopter of the human eyes can be obtained by acquiring the aberration of the human eyes. Due to the complexity of the human eye wavefront, Hartmann-Shack detection using optical track tracing is required to detect the wavefront. The Hartmann-Shack detector mainly comprises a micro-lens array and a CCD detector, wherein a light wave is divided into sub-light waves through the micro-lens array, the sub-light waves are focused on a focal plane through a lens to form a light spot array, the offset of each micro-lens in the x direction and the y direction is calculated by comparing the wavefront with aberration and the light spot array of a reference plane wave formed by mirror reflection, then the reconstruction of the wavefront aberration is carried out by utilizing a Zernike polynomial, the diopter of human eyes is obtained after the Zernike polynomial coefficient is obtained, and the focusing operation of an instrument is carried out by using the diopter.

The specific implementation mode of the invention is as follows:

1) Hartmann-Shack detection method for constructing optical track tracking

Based on a further understanding of the present invention, the detailed description will be made in conjunction with the probe optical path diagram (fig. 1). The light path structure mainly comprises two parts of modules, namely an incidence module and a reflection module.

In an incident module optical path, in order to avoid the influence of beam distortion caused by dispersion on measurement, a near-infrared laser beam generated by an 850nm laser light source 1 passes through a transparent turntable 2 to weaken the effect of dispersion, and the dispersion is eliminated by using the transparent rotary turntable 2. The light beam enters the focusing lens 3 from the turntable 2, is focused on the first polarization beam splitter prism 4 and then is reflected to the second polarization beam splitter prism 9, and then is reflected by the second polarization beam splitter prism 9 to enter the eye fundus of the human eye.

Since the light entering the eye first passes through the cornea, but the wave front formed by the light reflected by the cornea and the light passing through the retina re-exit pupil is different, the effect of the cornea will be affected if not eliminated. A polarizing beam splitter PBS was used, the principle of which is shown in figure 2. The PBS may split the incident beam into two linearly polarized light beams with mutually perpendicular directions of propagation, polarization P (transmission) and polarization S (reflection), respectively. Since the cornea of the human eye resembles a one-sided mirror, if the incoming polarized light S and the incoming polarized light P exist, the reflected light is the polarized light S and the polarized light P. If the incoming pure polarized light S is pure polarized light S, the reflected light is also pure polarized light S. However, pure polarized light S enters the eye, and exit pupil light reflected back from the retina contains both polarized light S and polarized light P. If the light entering the eyeball is pure polarized light S, the finally obtained polarized light P can be ensured to be light reflected by the retina.

However, the PBS cannot guarantee that all of the reflected polarized light S is polarized light S, and a very small amount of polarized light P is still included. Therefore, in order to eliminate the influence of the cornea as much as possible, the PBS is adopted in the light path instead of a reflecting mirror, and the two polarizing beam splitters PBS are used for eliminating the interference of the reflection of the cornea. The light beam comes out from the first polarization beam splitter 4 and is reflected to human eyes through the second polarization beam splitter 9, and the polarized light at the moment is similar to pure polarized light S. The pure polarized light S passes through the cornea and is reflected as polarized light S to the second polarizing beam splitter prism 9, but it is only reflected and not transmitted. Meanwhile, the entering polarized light S is reflected by the retina to exit the pupil, which contains the polarized light P, and then is transmitted when being reflected to the second polarization beam splitter prism 9. The corneal effects are thus eliminated.

In the reflection optical path module, the polarized light P is transmitted from the second polarization splitting prism 9 to the focusing lens 8, and enters the micro array lens 6 after passing through the collimator lens 7. The wavefront to be measured is converged on a focal plane to form a light spot array after passing through a micro-lens array lens. And acquiring a light spot array image through the detection of a CCD detector.

2) Method for calculating human eye diopter by reconstructing wave front aberration

After an ideal plane wave passes through the microlens array, the wavefront is focused at the focal plane of the microlens to form an array of spots. When the aberrated wavefront passes through the microlens array, the array of spots focused at the focal plane will be shifted. Therefore, the relative shift amount deltax and deltay of each microlens in the x and y directions can be calculated by comparing the ideal plane wave with the spot array with the wave front with aberration. The method comprises the steps of obtaining a light spot array image by using a CCD detector, carrying out noise suppression through OSTU threshold segmentation, obtaining the centroid position of each light spot, and then determining the centroid offset of the light spots so as to calculate the wavefront slope. The algorithm flow chart is shown in fig. 3:

according to geometric optics, the relative displacement of the spot is proportional to the local slope at that point, so the wavefront slopes in the two orthogonal directions x and y are:

In order to avoid errors caused by the fact that the various equations influence each other due to the lack of orthogonality in the process of fitting the wavefront aberration, the selected wavefront reconstruction algorithm needs the polynomial to have the orthogonal characteristic and the optical aberration correspondence, and therefore the Zernike polynomial is selected as the wavefront reconstruction algorithm. The wavefront is expressed by a Zernike polynomial:

by substituting formula 3 for formulae 1 and 2, one can obtain:

then order

Writing equations

6, 7, 8, 9 in the form of a matrix:

3) Focusing by using human eye diopter to drive instrument

The object and image distances are shown in fig. 4 below.

According to the lens imaging formula in optics:

the size of the image distance can be changed by adjusting the size of the object distance. Therefore, the following optical path structure can be used to adjust the distance of the imaging focus, as shown in fig. 5:

when the human eye cannot image clearly on the retina by refraction, such as:

if the refractive power of the eyeball of the human eye is too weak or the axis of the eye is too long, an object at infinity can be imaged in front of the retina, and the human eye is a myopic eye. If the refractive power of the eyeball of the human eye is too strong or the axis of the eye is too short, an infinitely distant object is imaged behind the retina, the human eye is a hypermetropia eye.

Therefore, refractive correction can be performed by the structure shown in fig. 5, so that an infinitely distant object can be correctly imaged on the retina.

The parallel light is focused by the first lens 10, coupled by the second lens 11 and finally passes through the third lens 12, and if the human eye is dioptrically imaged in front of the retina, the positions of the second lenses 11 to 11.3 can be adjusted. If imaging is to be performed behind the retina, the position of the second lens 11 can be adjusted to 11.1, so that ambient light can be focused on the retina. Therefore, the position of the second lens 11 can be adjusted to change the propagation direction of the light before entering the human eyes so as to influence the refraction condition of the light in the human eyes, and the effect of measuring the light by the instrument and focusing the light on the retina of the human eyes is achieved, so that an image can be formed on the retina.

The diopter of human eyes can be obtained in the step 2, the position of the second lens 11 can be rapidly adjusted by driving and adjusting a motor of the second lens 11 according to the position relation between the diopter and the second lens 11, so that an image can be clearly formed on a retina, the automatic focusing function is realized, the diopter of the human eyes is measured by using a Hartmann shack (H-S) detection method, and then the position of the lens is automatically adjusted by using the position relation between the diopter and the lens, so that the automatic focusing is realized.

Finally, it should be noted that: although the present invention has been described in detail with reference to the embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments or portions thereof without departing from the spirit and scope of the invention.

Claims

1. the optical instrument focusing method based on H-S reconstruction of human eye wavefront aberration, is characterized in that, comprises the following steps: adopt the Hartmann-Shack detection method of light trace tracing to detect wavefront, and light wave can be divided through microlens array The sub-light waves are focused on the focal plane through the lens to form a light spot array, and the x and y directions of each microlens are calculated by comparing the wavefront with aberration and the light spot array of the reference plane wave formed by specular reflection. Then, the Zernike polynomial is used to reconstruct the wavefront aberration, and the Zernike polynomial coefficient is obtained to obtain the diopter of the human eye and use this to perform the focusing operation of the instrument.

2. the optometry instrument focusing method based on the H-S reconstruction of human eye wavefront aberration according to claim 1, is characterized in that, the Hartmann-Shack detection method that builds trace tracing comprises incident module and reflection module, in incident module optical path , in order to first generate a near-infrared laser beam from a laser light source through a transparent turntable to reduce dispersion, exit from the turntable and enter the focusing lens, focus on the first polarized beam splitter prism, then reflect to the second polarized beam splitter prism, and then split by the second polarized beam splitter The prism reflects into the fundus of the human eye; the light entering the eye first passes through the cornea, and part of the light reflected by the cornea is transmitted from the second polarized beam splitter prism to the focusing lens, and then enters the microarray lens through the collimating lens, and then converges on the microlens array lens. The focal plane forms a light spot array, and the light spot array image is acquired by the detection of the CCD detector.

3 . The focusing method for an optometry instrument based on H-S reconstruction of human eye wavefront aberration according to claim 2 , wherein the laser light source is an 850 nm laser light source. 4 .

4. the optical instrument focusing method based on H-S reconstruction of human eye wavefront aberration according to claim 2, is characterized in that, reconstructed wavefront aberration seeks human eye diopter: after an ideal plane wave passes through the microlens array, The wavefront is focused on the focal plane of the microlens to form a light spot array. When the wavefront with aberration passes through the microlens array, the light spot array focused on the focal plane will be offset. The spot array with poor wavefront can calculate the relative offsets Δx and Δy of each microlens in the x and y directions, use the CCD detector to obtain the spot array image, perform noise suppression through OSTU threshold segmentation, and obtain each spot. The position of the centroid of the light spot, and then determine the offset of the centroid of the light spot, the wavefront slope can be calculated, and the Zernike polynomial is selected as the wavefront reconstruction algorithm, and the Zernike polynomial coefficient can be obtained to reconstruct the wavefront aberration of the human eye. number.

5. the optical instrument focusing method based on H-S reconstruction of human eye wavefront aberration according to claim 4, it is characterized in that, according to geometric optics, the relative displacement of the light spot is proportional to the local slope at this point, so x The wavefront slopes in the two orthogonal directions of , y are:

where W(x,y) is the incident wavefront aberration, and f is the focal length of the microlens.

6. the optometry instrument focusing method based on H-S reconstruction of human eye wavefront aberration according to claim 5, is characterized in that,

Represent the wavefront in terms of Zernike polynomials:

Substituting Equation 3 into Equation 1 and Equation 2, we get:

then make

Write equations 6, 7, 8, and 9 in matrix form:

In the above matrix, the ω _j matrix is the coefficient matrix of the reconstructed wavefront, and the above formula is written as β=αω→α ^T β=α ^T αω→ω=(α ^T α) ^-1 α ^T β= alpha ⁺ beta

The wavefront aberration of the human eye can be reconstructed by obtaining the Zernike polynomial coefficient, and the diopter can be calculated according to the following formula:

Among them, R is the pupil radius, C is the cylindrical power, S is the spherical power, and ω ₄ , ω ₅ , and ω ₆ are the Zernike polynomial coefficients.

7. the optical instrument focusing method based on H-S reconstruction of human eye wavefront aberration according to claim 6, is characterized in that, utilizes human eye diopter to drive instrument focusing: according to the positional relationship of diopter and the second lens, thereby can drive The motor for adjusting the second lens quickly adjusts the position of the second lens, so that the image can be clearly formed on the retina, thereby realizing the function of automatic focusing.