Method for measuring human eye astigmatism based on OCT

Abstract

The present invention provides a method for measuring human eye astigmatism based on optical coherence tomography (OCT), relating to the field of computer technology. The method utilizes a swept-frequency optical coherence tomography (OCT) device to capture images of ocular structures, obtaining swept-frequency OCT images. The captured swept-frequency OCT images are processed to obtain a reconstructed model of the cornea and lens. Within the reconstructed model, 12 meridians centered on the pupil are selected for incision to obtain the thickness of the cornea and lens, as well as the curvature of the anterior and posterior surfaces. The refractive power of the eye, cornea, and lens is calculated using a formula: The total refractive power at each of the 640 points on the 12 meridians of the human eye is calculated using a formula, and the maximum and minimum values ​​of the total refractive power are determined. The difference between the maximum and minimum values ​​is equal to the amplitude M of the astigmatism.

Description

Technical Field

[0001] The present invention relates to the field of computer technology, and in particular to a method for measuring human eye astigmatism based on OCT. Background Art

[0002] Astigmatism is a refractive error caused by differences in the refractive power of light on different meridians of the eye, resulting in two focal lines and a spot of minimum diffusion. Both the cornea and the lens significantly influence astigmatism. Astigmatism can cause vision loss, visual fatigue, and even dizziness and headaches. Without accurate measurement, we cannot precisely correct and treat astigmatism based on the patient's actual condition.

[0003] The cornea and lens, as the main parts of the eye's refractive system, play an important role in the eye's refractive power. Currently, astigmatism is mainly determined by various parameters of the anterior corneal surface. In practical applications, existing equipment and methods for measuring astigmatism are not able to measure the cornea and lens well. The main reasons are as follows:

[0004] 1. Keratometer: Keratometer is a method based on measurements of the anterior corneal surface. Keratometers use empirical corneal measurement indices to extrapolate the refractive power of the posterior corneal surface, a method with inherent bias. Furthermore, its limited measurement range makes it generally unreliable for measuring astigmatism.

[0005] 2. IOL-Master500: It uses telecentric optics and optical reflection principles to measure astigmatism. Although the measurement is relatively fast and repeatable, the measurement results cannot reflect the entire corneal morphology and are greatly affected by the stability of the tear film. In addition, it cannot fully measure the entire surface of the cornea.

[0006] 3. Pentacam: This system is a 3D anterior segment analysis and diagnostic system that uses the Scheimpflug imaging principle for rotational scanning. Its built-in Scheimpflug camera can capture 50 coaxial slit images within 2 seconds, deriving corneal curvature and refractive power from the height. However, its measurements are affected by corneal transparency and cannot penetrate a cloudy cornea.

[0007] 4. Optical Coherence Tomography (OCT): This method offers high resolution and can capture images of all layers of the eye, allowing visualization and measurement of various ocular structures. It offers higher image quality and can be used to obtain parameters related to various ocular structures. Spectral OCT is currently the most commonly used method, but its detection range does not meet practical application needs.

[0008] By comparison, swept-frequency OCT has higher precision and accuracy in evaluating eye astigmatism. Swept-frequency OCT has higher resolution and deeper detection range, which can better measure the structure of the human eye.

[0009] If we can use existing high-precision instruments and design a precise method to measure astigmatism, and accurately determine the degree and axis of astigmatism, it will undoubtedly greatly improve the detection level of astigmatism in the human eye and achieve early correction and treatment of astigmatism. Summary of the Invention

[0010] In response to the shortcomings of the existing technology, the present invention provides a method for measuring human eye astigmatism based on OCT. A swept-frequency OCT device can accurately capture images of the human eye structure, and combined with image processing technology, relevant parameters of various structures of the human eye are calculated, and then the astigmatism is quantitatively evaluated through relevant algorithms.

[0011] A method for measuring human eye astigmatism based on OCT, comprising the following steps:

[0012] Step 1: Use a swept-frequency OCT device to acquire images of the eye structure and obtain a swept-frequency OCT image;

[0013] Step 2: Perform pixel and grayscale correction on the acquired swept-frequency OCT images, detect the anterior and posterior surfaces of the cornea and the anterior and posterior surfaces of the lens, enhance the edges, extract the surface contours, and store them in the established 3D data set; use the 3D data set to fit the anterior and posterior surfaces of the cornea and the lens, and then use optical distortion correction, sector distortion correction, and optical refraction distortion correction to retrieve the 3D data of the anterior and posterior surfaces of the cornea and the lens. Then, correct the surface contours of the cornea and lens, and finally perform 3D reconstruction of the anterior and posterior surfaces of the cornea and lens, respectively, to obtain reconstructed models of the cornea and lens;

[0014] Step 3: Select 12 meridians centered on the pupil in the reconstructed model for cutting. The meridians are evenly distributed from 0° to 180°. 640 points are taken on each meridian to obtain the thickness of the cornea and lens and the curvature of the front and back surfaces. The refractive power of the eye, cornea, and lens is calculated using the formula:

[0015]

[0016]

[0017]

[0018] Among them, P, P C and P L are the refractive powers of the eye, cornea, and lens, nh and n l is the refractive index of aqueous humor and lens, R c 、R a and R p is the radius of curvature of the cornea, anterior lens, and posterior lens, ACD is the anterior chamber depth, and LT is the thickness of the lens;

[0019] Step 4: Use the formula to calculate the total diopter at each of the 640 points on the 12 meridians of the human eye (uniformly distributed from 0° to 180°), and find the maximum and minimum values ​​of the total diopter. The difference between the maximum and minimum values ​​is equal to the amplitude of astigmatism M. The angle of the corneal meridian corresponding to the maximum value of the total diopter is the astigmatism angle α, and the astigmatism axis is It is perpendicular to the astigmatism angle, that is

[0020] The beneficial effects of adopting the above technical solution are:

[0021] The present invention provides a method for measuring human eye astigmatism based on OCT, which has the following beneficial effects:

[0022] 1. The device uses a non-contact, non-invasive measurement method and basically does not cause any damage to the patient's body.

[0023] 2. OCT has higher resolution and deeper detection depth. It can be used to evaluate eye refractive power with higher precision and accuracy, and can better measure the structure of the eye.

[0024] 3. Traditional methods for measuring astigmatism rely solely on measurements of the anterior corneal surface, without considering the effects of other ocular structures. Our method utilizes three-dimensional reconstruction of the anterior and posterior corneal surfaces and the anterior and posterior surfaces of the lens, extracting relevant parameters. This allows our proposed measurement method to account for the effects of the entire ocular structure on astigmatism, enabling a more accurate determination of the patient's astigmatism and its corresponding axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is an overall flow chart of the astigmatism measurement method in an embodiment of the present invention;

[0026] Figure 2 is a schematic structural diagram of an OCT device in an embodiment of the present invention;

[0027] Figure 3 is a surface contour extraction diagram in an embodiment of the present invention; DETAILED DESCRIPTION

[0028] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0029] A method for measuring human eye astigmatism based on OCT, such as Figure 1 As shown, the following steps are included:

[0030] Step 1: Use Figure 2 The swept-frequency OCT device shown in the figure acquires images of the patient's ocular structure and obtains swept-frequency OCT images. The light source uses 1300nm, which can achieve an axial resolution of 7.5μm and an imaging depth of up to 10mm. It can measure and image the eyes of patients with different degrees of astigmatism.

[0031] Step 2: Perform pixel and grayscale correction on the acquired swept-frequency OCT image, detect the anterior and posterior surfaces of the cornea and the anterior and posterior surfaces of the lens, perform enhancement processing, extract the surface contours, and store them in the established three-dimensional data set; use the three-dimensional data set to fit the anterior and posterior surfaces of the cornea and the anterior and posterior surfaces of the lens, then perform optical distortion correction, adopt sector distortion correction and optical refraction distortion correction to retrieve the three-dimensional data of the anterior and posterior surfaces of the cornea and the anterior and posterior surfaces of the lens, then correct the surface contours of the cornea and the lens, and finally perform three-dimensional reconstruction of the anterior and posterior surfaces of the cornea and the lens, respectively, to obtain reconstructed models of the cornea and the lens. In this embodiment, MATLAB, a commercial mathematical software produced by MathWorks, is used;

[0032] Step 3: Select 12 meridians centered on the pupil in the reconstructed model for cutting. The meridians are evenly distributed from 0° to 180°. 640 points are taken on each meridian to obtain the thickness of the cornea and lens and the curvature of the front and back surfaces. The refractive power of the eye, cornea, and lens is calculated using the formula:

[0033]

[0034]

[0035]

[0036] Among them, P, P C and P L are the refractive powers of the eye, cornea, and lens, n h and n l is the refractive index of aqueous humor and lens, R c 、R a and R p is the radius of curvature of the cornea, anterior lens, and posterior lens, ACD is the anterior chamber depth, and LT is the thickness of the lens;

[0037] Step 4: Use the formula to calculate the total diopter at each of the 640 points on the 12 meridians of the human eye (uniformly distributed from 0° to 180°), and find the maximum and minimum values ​​of the total diopter. The difference between the maximum and minimum values ​​is equal to the amplitude of astigmatism M. The angle of the corneal meridian corresponding to the maximum value of the total diopter is the astigmatism angle α, and the astigmatism axis is It is perpendicular to the astigmatism angle, that is

[0038] like Figure 3 The figure shows contour extraction of the anterior and posterior surfaces of the cornea and the lens. In this example, pixel and grayscale corrections are performed on the original image of the patient's eye obtained using swept-frequency OCT. Contours of the anterior and posterior surfaces of the cornea and the lens are then extracted and stored in a built 3D dataset.

[0039] The above description is merely a preferred embodiment of the present disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also encompass other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the above-mentioned inventive concept. For example, a technical solution formed by mutually replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in the embodiments of the present disclosure.

Claims

1. A method for measuring human eye astigmatism based on OCT, characterized in that: The following steps are involved: Step 1: Use a swept-frequency OCT device to acquire images of the eye structure and obtain a swept-frequency OCT image; Step 2: Perform pixel and grayscale correction on the acquired swept-frequency OCT images, detect the anterior and posterior surfaces of the cornea and the anterior and posterior surfaces of the lens, enhance the edges, extract the surface contours, and store them in the established 3D data set; use the 3D data set to fit the anterior and posterior surfaces of the cornea and the lens, and then use optical distortion correction, sector distortion correction, and optical refraction distortion correction to retrieve the 3D data of the anterior and posterior surfaces of the cornea and the lens. Then, correct the surface contours of the cornea and lens, and finally perform 3D reconstruction of the anterior and posterior surfaces of the cornea and lens, respectively, to obtain reconstructed models of the cornea and lens; Step 3: Select 12 meridians centered on the pupil in the reconstructed model and cut them. 640 points are taken on each meridian to obtain the thickness of the cornea and lens and the curvature of the anterior and posterior surfaces. The refractive power of the eye, cornea, and lens is calculated using formulas. The refractive power of the eye, cornea and lens: Among them, P, P C and P L are the refractive powers of the eye, cornea, and lens, n h and n l is the refractive index of aqueous humor and lens, R c 、R a and R p is the radius of curvature of the cornea, anterior lens, and posterior lens, ACD is the anterior chamber depth, and LT is the thickness of the lens; Step 4: Use the formula to calculate the total refractive power at each of the 640 points on the meridian, and find the maximum and minimum values ​​of the total refractive power. The difference between the maximum and minimum values ​​is equal to the amplitude of astigmatism M. The angle of the corneal meridian corresponding to the maximum value of the total refractive power is the astigmatism angle α, and the astigmatism axis is It is perpendicular to the astigmatism angle, that is 2. The method for measuring human eye astigmatism based on OCT according to claim 1, characterized in that: The meridians are evenly distributed from 0° to 180°.

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