CN113034608B - Corneal surface morphology measuring device and method - Google Patents
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- 238000012876 topography Methods 0.000 claims description 24
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- 238000006243 chemical reaction Methods 0.000 abstract description 2
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- 238000000691 measurement method Methods 0.000 description 4
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- 238000004445 quantitative analysis Methods 0.000 description 2
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- 238000010252 digital analysis Methods 0.000 description 1
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- 208000037265 diseases, disorders, signs and symptoms Diseases 0.000 description 1
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- 208000030533 eye disease Diseases 0.000 description 1
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- 230000002980 postoperative effect Effects 0.000 description 1
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/80—Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
- G06T7/85—Stereo camera calibration
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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
- A61B3/107—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for determining the shape or measuring the curvature of the cornea
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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
- A61B3/14—Arrangements specially adapted for eye photography
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Abstract
The invention provides a corneal surface morphology measuring device and a method, which are characterized in that firstly, a binocular camera system is used for acquiring an image of a cornea containing dot matrix light spots, then, three-dimensional coordinates of each measuring point are calculated through coordinate conversion, all the three-dimensional coordinate points are used for obtaining an approximate spherical surface where the cornea is located by utilizing a curved surface fitting method, and finally, a Gaussian diopter at each measuring point is calculated, and a corneal topographic map is generated by combining operations such as a data field interpolation method, a color coding method and the like.
Description
Technical Field
The invention relates to the technical field of medical examination, in particular to a corneal surface morphology measuring device and method.
Background
In recent years, corneal topography measurement has become an important part of eye visual optics research and clinical application, and corneal topography is a systematic and comprehensive quantitative analysis means for studying corneal anterior surface morphology, wherein corneal topography is a digital analysis of corneal topography by a computer image processing system, and obtained information is represented by a color map with different characteristics, which is called corneal topography because of the apparent topographic surface height state in geography, and can accurately measure and analyze the curvature of any point on the total corneal anterior surface and detect corneal refractive power. The corneal topography is applied to diagnosis of corneal astigmatism and quantitative analysis of corneal properties, can also be used for preoperative examination and postoperative curative effect evaluation of corneal refractive surgery and corneal transplantation surgery, provides a large amount of corneal morphological information for researchers, and becomes an essential measuring tool for ophthalmology and visual optics.
The cornea topographer most commonly used at present mainly consists of a Placido plate projection system, a real-time image detection system and a computer image processing system, and is finally presented in the form of data or images. The cornea topographer has the advantages of large measurement range, high accuracy and the like. However, the measurement process is very complicated, and requires horizontal and vertical adjustment of the device, so that the first light-emitting point is aligned with the center of the mark and the center of the cornea, which requires a lot of time for adjustment, and the characteristic of which makes it difficult to perform measurement on a patient in a hand-held manner. Obtaining accurate corneal topography is difficult, especially for children who cannot maintain a fixed posture and coordinate measurements.
The newborn eyeball is small and is a physiological presbyopia, and in the growth and development process of the newborn eyeball, the axis of the eye is matched with refractive media such as cornea, crystalline lens, vitreous body and the like, and the mutual influence gradually reaches emmetropization. The cornea curvature variation degree of infants under three years old is large, and especially the cornea curvature degree and the astigmatism degree of infants less than three months are large. Therefore, the detection of the corneal topography is important for the development of eyes of infants, and if the eyes can be found and treated early, the ophthalmic diseases caused by the early finding can be prevented, and the situations of near, far, astigmatism, keratopathy and the like can be effectively reduced. Therefore, the cornea topographer is very important for detecting the condition of the eyeball of the child, and the cornea topographer is an indispensable instrument for detecting the condition of the eyeball.
However, since the conventional corneal topographer requires a complicated measurement process, requires a high level of eyeball condition for the subject, and requires a high level of fitting for the subject, it is difficult to obtain an accurate corneal topography for children who cannot maintain a fixed posture and fit measurement.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a corneal surface morphology measuring device which is characterized by comprising a camera I, a camera II, a dot matrix light source, a calculation processing module and a display module, wherein the camera I, the camera II and the dot matrix light source are respectively and electrically connected with the calculation processing module, and the calculation processing module is electrically connected with the display module;
the lattice light source is used for emitting lattice light, and lattice light spots are formed on the surface of the cornea of the eye as target points;
the camera is used for shooting an eye cornea image with a dot matrix light spot and sending the image to the calculation processing module;
the calculation processing module is used for solving the three-dimensional coordinates of the target points, fitting the three-dimensional coordinates according to the target points to obtain the spherical surface where the cornea is located, then obtaining a corneal topographic map by solving the Gaussian diopter of each target point, and also used for controlling the on-off state of the dot matrix light source;
the display module is used for displaying the corneal topography.
A measurement method using the corneal topography measuring apparatus, comprising the steps of:
step 1: calibrating parameters and distortion coefficients of a binocular camera system consisting of a camera I and a camera II to obtain an internal parameter matrix K and distortion coefficients of the camera;
and 2, step: a dot matrix light source is used for emitting dot matrix light, and dot matrix light spots are formed on the surface of the cornea of the eye and serve as target points;
and 3, step 3: respectively shooting the cornea of the eye by a camera I and a camera II which are arranged on the same horizontal plane and have a distance L;
and 4, step 4: performing distortion removal on images shot by the two cameras to obtain two-dimensional coordinates (m, n) of the target point on an imaging plane C1 and two-dimensional coordinates (m ', n') on an imaging plane C2, wherein the imaging plane C1 refers to an imaging plane of the camera I, and the optical center of the imaging plane C1 is recorded as C 1 The imaging plane C2 refers to the imaging plane of camera II, and the optical center of the imaging plane C2 is denoted as C 2 ；
And 5: with c 1 As the origin of the three-dimensional coordinate system, with c 1 、c 2 The straight line establishes the X axis of the coordinate system for imagingThe direction perpendicular to the X axis in the plane establishes the Y axis, the direction perpendicular to the normal vector of the imaging plane establishes the Z axis, and the optical center c is recorded 1 Has coordinates of (0,0,0) and optical center c 2 The coordinates of (d) are (L,0, 0);
and 6: respectively calculating the three-dimensional coordinates of the imaging points of the target point on two imaging planes according to the internal parameter matrix K, wherein the imaging point g of the target point on the imaging plane C1 1 The three-dimensional coordinates (X, Y,0) of (a) are calculated as follows:
imaging point g of target point on imaging plane C2 2 Is calculated as follows:
and 7: using optical centre c 1 Image point g 1 Establish the equation of a straight line L1 using the optical center c 2 Image point g 2 Establishing a linear equation L2, and solving an intersection G of the straight lines L1 and L2 0 Then point of intersection G 0 Coordinate (x) of (2) t ,y t ,z t ) That is, the coordinates of the target point, where the calculated three-dimensional coordinates are respectively expressed as:
wherein F is the focal length of the camera;
and 8: fitting by using a least square method according to the obtained target point coordinates to obtain a spherical equation where the cornea is located;
and step 9: and solving the Gaussian diopter of each target point on the spherical surface to obtain a corneal topography.
The step 8 comprises the following steps:
step 8.1: according to the n target point coordinates { (x) 1 ,y 1 ,z 1 ),(x 2 ,y 2 ,z 2 ),…,(x t ,y t ,z t ),…,(x n ,y n ,z n ) The solution equation for constructing the sphere to be fitted is as follows:
in the formula (I), the compound is shown in the specification,
a matrix of coefficients is represented by a matrix of coefficients,
a representation of the observation vector is shown,
representing parameters to be estimated, t is 1,2, …, n, r represents the radius of the sphere to be fitted, and a, b and c represent the parameters to be estimated of the sphere to be fitted;
step 8.2: converting the formula (4) into U ═ A T A) -1 A T And B, substituting n target point coordinates, solving specific values of a, B, c and r by using a least square method, and determining a determined equation of the spherical surface to be fitted as a spherical surface equation of the cornea.
The step 9 comprises:
step 9.1: rotating a normal plane of the target point, which is intersected with the spherical surface on the spherical surface, by taking a normal line as a symmetry axis, calculating curvature radii along all tangential directions, taking the maximum curvature and the minimum curvature, and converting the maximum curvature and the minimum curvature into diopter;
step 9.2: calculating the average value of the diopter of the maximum curvature and the diopter of the minimum curvature to obtain Gaussian diopter;
step 9.3: repeating the step 9.1 to the step 9.2, and calculating the Gauss diopter of all the target points;
step 9.4: and (3) carrying out grid division on a data field formed by all Gaussian refraction values, solving the data value of an unknown point by a data field interpolation method, and then carrying out color coding processing to finally form a corneal topography.
The invention has the beneficial effects that:
the invention provides a corneal surface morphology measuring device and a method, firstly, an eye cornea image containing lattice faculae is obtained through a binocular camera system, then, the three-dimensional coordinates of each measuring point are calculated through coordinate conversion, all the three-dimensional coordinate points are used for obtaining an approximate spherical surface where the cornea is located by utilizing a curved surface fitting method, finally, the Gaussian diopter of each measuring point is calculated, and the corneal topographic map is generated by combining the data field interpolation method, the color coding and other operations. The device can be integrated into a handheld end, is suitable for carrying out the detection of cornea to the infant, conveniently screens early eye disease.
Drawings
FIG. 1 is a block diagram of a corneal topography measuring device according to the present invention;
FIG. 2 is a flow chart of a measurement method based on corneal topography measurement according to the present invention;
FIG. 3 is a schematic diagram of a measurement method according to the present invention;
in the figure, 1, an object point, 2, an optical center of a camera I, 3, an optical center of a camera II, 4, an imaging plane C1, 5 of the camera I, an imaging plane C2, 6 of the camera II, an imaging point of the object point on an imaging plane C1, 7, an imaging point of the object point on an imaging plane C2, 8, a center point of an imaging plane C1, 9, and a center point of an imaging plane C2.
Detailed Description
The invention is further described with reference to the accompanying drawings and the embodiments, the method does not require corneal centring, and compared with the current methods, the method is simple and quick to operate and requires less cooperation with infants.
As shown in fig. 1, a corneal topography measuring device comprises two cameras I, a camera II, a dot matrix light source, a calculation processing module and a display module, wherein the camera I, the camera II and the dot matrix light source are respectively electrically connected with the calculation processing module, and the calculation processing module is electrically connected with the display module;
the dot matrix light source is used for emitting dot matrix light, and dot matrix light spots are formed on the surface of the cornea of the eye to serve as target points;
the camera is used for shooting an eye cornea image with a dot matrix light spot and sending the image to the calculation processing module;
the calculation processing module is used for solving the three-dimensional coordinates of the target points, fitting the three-dimensional coordinates according to the target points to obtain the spherical surface where the cornea is located, then obtaining a corneal topographic map by solving the Gaussian diopter of each target point, and further controlling the on-off state of the dot matrix light source;
the display module is used for displaying the corneal topography.
The model of the components adopted in this embodiment is as follows: the two cameras are DH-GPP1080P USB binocular camera modules; the lattice light source is a HW520AD35-16GD lattice laser emission module; the calculation processing module is a Raspberry Pi 3B + development board; the display module is a 4inch HDMI LCD display screen; the method comprises the steps that cornea images are collected from different directions through two cameras and then transmitted to a calculation processing module, the calculation processing module constructs an approximate spherical surface where a cornea is located through three-dimensional coordinates of an extraction target point, a Gaussian diopter without determining the position of the vertex of the cornea is adopted as a numerical form of a cornea topographic map, then color coding processing is carried out to form the cornea topographic map, finally the cornea topographic map is displayed through a display module, the cameras, a dot matrix light source, the calculation processing module and the display module can be integrated into a whole handheld instrument, and a user can complete measurement on a detected person only through the handheld instrument.
The specific measurement principle is as shown in fig. 3, dot matrix light is emitted by a dot matrix light source, dot matrix light spots are formed on the surface of the cornea, images are simultaneously shot by a camera I and a camera II, the images are processed and calculated by a calculation processing module, the intersection point of the connecting line of a target point 1 and a left optical center 2 and a left imaging plane 4 is an image 6 formed by the target point on the left imaging plane 4, the intersection point of the connecting line of the target point 1 and a right optical center 3 and a right imaging plane 5 is an image 7 formed by the target point on a right imaging plane 5, and the three-dimensional coordinates of the target point are solved under the condition that the three-dimensional coordinates of the left imaging point 6, the right imaging point 7, the left camera optical center 2 and the right camera optical center 3 are known.
As shown in fig. 2, a measurement method using a corneal surface morphology measurement device is implemented by using a Raspberry Pi 3B + development board carrying an OpenCV vision development library and matlab software design, and includes:
step 1: calibrating parameters and distortion coefficients of a binocular camera system consisting of a camera I and a camera II to obtain an internal parameter matrix K and distortion coefficients of the camera; during calibration, checkerboards with a fixed format can be printed by matlab software, then the checkerboards are shot by a camera, and then the pictures are led into the matlab software to complete the calibration process through the calibration function.
Step 2: a dot matrix light source is used for emitting dot matrix light, and dot matrix light spots are formed on the surface of the cornea of the eye and serve as target points;
and step 3: respectively shooting the cornea of the eye by a camera I and a camera II which are arranged on the same horizontal plane and have a distance L;
because the detection object is the cornea surface of the eye, after the spot array is irradiated on the cornea surface, the obtained light spot is similar to a square spot array. In an image shot by a camera, firstly, finding out light spots closest to the pixels at the upper left and the lower right of the image according to the coordinates of the light spots in the image, marking the light spots as the angular points at the upper left and the lower right, calculating a regular lattice similar to a lattice light source by taking the two points as the upper left angular point and the lower right angular point of the lattice, traversing the point coordinates of the lattice in the image one by one, finding out the light spots closest to the currently traversed point coordinates, and recording the values of the light spots and the rows and columns in the regular lattice to be the same. The above steps are performed on the images of camera I and camera II, respectively. In the images of the camera I and the camera II, the light spots with the same row and column values are the results of the same target point respectively captured by the camera I and the camera II.
And 4, step 4: carrying out distortion removal processing on images shot by the two cameras by using an OpenCV (open CV) library distortion removal algorithm to obtain two-dimensional coordinates (m, n) of the target point on an imaging plane C1 and two-dimensional coordinates (m ', n') on an imaging plane C2, wherein the imaging plane C1 refers to an imaging plane of the camera I, and the optical center of the imaging plane C1 is recorded asc 1 The imaging plane C2 refers to the imaging plane of camera II, and the optical center of the imaging plane C2 is denoted as C 2 ；
And 5: with c 1 As the origin of the three-dimensional coordinate system, with c 1 、c 2 The X axis of the coordinate system is established on the straight line, the Y axis is established in the direction vertical to the X axis in the imaging plane, the Z axis is established in the direction vertical to the normal vector of the imaging plane, and the light recording center c 1 Has coordinates of (0,0,0) and optical center c 2 The coordinates of (d) are (L,0, 0);
and 6: respectively calculating the three-dimensional coordinates of the imaging points of the target point on two imaging planes according to the internal parameter matrix K, wherein the imaging point g of the target point on the imaging plane C1 1 The three-dimensional coordinates (X, Y,0) of (a) are calculated as follows:
imaging point g of target point on imaging plane C2 2 The three-dimensional coordinates (X ', Y',0) of (a) are calculated as follows:
and 7: using optical centre c 1 Image point g 1 Establish the equation of a straight line L1 using the optical center c 2 An image point g 2 Establishing a linear equation L2, and solving an intersection G of the straight lines L1 and L2 0 Then point of intersection G 0 Coordinate (x) of t ,y t ,z t ) That is, the coordinates of the target point, where the calculated three-dimensional coordinates are respectively expressed as:
wherein, F is the focal length of the camera and is contained in an internal parameter matrix during calibration;
because the cornea surface is approximate to a spherical surface, the point cloud data of the cornea surface can be utilized to carry out spherical surface fitting, namely, the spherical center coordinates and the spherical radius are obtained according to a certain number of spherical points.
The known spherical equation is: r is 2 ＝(x-a) 2 +(y-b) 2 +(z-c) 2
Wherein (a, b, c) are coordinates of the center of sphere, r is the radius of sphere, and (x, y, z) are coordinates of points on the sphere;
the spherical equation is developed as follows:
x 2 +y 2 +z 2 ＝2xa+2yb+2zc+r 2 -a 2 -b 2 -c 2 ；
in the formula, a, b, c and r 2 -a 2 -b 2 -c 2 Regarded as the parameter to be estimated;
and 8: and obtaining a spherical equation of the cornea according to the obtained target point coordinates by using least square fitting, wherein the spherical equation comprises the following steps:
step 8.1: according to the n target point coordinates { (x) 1 ,y 1 ,z 1 ),(x 2 ,y 2 ,z 2 ),…,(x t ,y t ,z t ),…,(x n ,y n ,z n ) The solving equation for constructing the spherical surface to be fitted is as follows:
in the formula (I), the compound is shown in the specification,
a matrix of coefficients is represented by a matrix of coefficients,
a representation of the observation vector is shown,
the parameters to be estimated are represented, t is 1,2, …, n, r represents the radius of the spherical surface to be fitted and also the approximate curvature radius of the corneal surface, and a, b and c represent the parameters to be estimated of the spherical surface to be fitted;
step 8.2: converting the formula (4) into U ═ A T A) -1 A T And B, substituting n target point coordinates, solving specific values of a, B, c and r by using a least square method, and determining a determined equation of the spherical surface to be fitted as a spherical surface equation of the cornea.
And step 9: solving the Gaussian diopter of each target point on the spherical surface to obtain a corneal topography, wherein the corneal topography comprises the following steps:
step 9.1: calculating a normal plane of the target point, which is intersected with the spherical surface on the spherical surface, rotating the normal plane by taking a normal as a symmetry axis, calculating curvature radiuses along all tangential directions, taking a maximum curvature and a minimum curvature, and converting the maximum curvature and the minimum curvature into diopter;
step 9.2: calculating the average value of the diopter of the maximum curvature and the diopter of the minimum curvature to obtain Gaussian diopter;
step 9.3: repeating the step 9.1 to the step 9.2, and calculating the Gauss diopter of all the target points;
step 9.4: and (3) carrying out grid division on a data field formed by all Gaussian refraction values, solving the data value of an unknown point by a data field interpolation method, carrying out color coding processing, identifying different heights of the topographic map, and finally forming the corneal topographic map.
Claims (3)
1. A corneal surface morphology measuring method is realized by adopting a corneal surface morphology measuring device, wherein the measuring device comprises a camera I, a camera II, a dot matrix light source, a calculation processing module and a display module, the camera I, the camera II and the dot matrix light source are respectively and electrically connected with the calculation processing module, and the calculation processing module is electrically connected with the display module; the dot matrix light source is used for emitting dot matrix light, and dot matrix light spots are formed on the surface of the cornea of the eye to serve as target points; the camera is used for shooting an eye cornea image with a dot matrix light spot and sending the image to the calculation processing module; the calculation processing module is used for solving the three-dimensional coordinates of the target points, fitting the three-dimensional coordinates according to the target points to obtain the spherical surface where the cornea is located, then obtaining a corneal topographic map by solving the Gaussian diopter of each target point, and further controlling the on-off state of the dot matrix light source; the display module is used for displaying the corneal topography; characterized in that the method comprises:
step 1: calibrating parameters and distortion coefficients of a binocular camera system consisting of a camera I and a camera II to obtain an internal parameter matrix K and distortion coefficients of the camera;
step 2: a dot matrix light source is used for emitting dot matrix light, and dot matrix light spots are formed on the surface of the cornea of the eye and serve as target points;
and step 3: respectively shooting the cornea by a camera I and a camera II which are arranged on the same horizontal plane and have a distance L between each other;
and 4, step 4: performing distortion removal on images shot by the two cameras to obtain two-dimensional coordinates (m, n) of the target point on an imaging plane C1 and two-dimensional coordinates (m ', n') on an imaging plane C2, wherein the imaging plane C1 refers to an imaging plane of the camera I, and the optical center of the imaging plane C1 is recorded as C 1 The imaging plane C2 refers to the imaging plane of camera II, and the optical center of the imaging plane C2 is denoted as C 2 ；
And 5: with c 1 As the origin of the three-dimensional coordinate system, with c 1 、c 2 The X axis of the coordinate system is established on the straight line, the Y axis is established in the direction vertical to the X axis in the imaging plane, the Z axis is established in the direction vertical to the normal vector of the imaging plane, and the light recording center c 1 Has coordinates of (0,0,0) and optical center c 2 The coordinates of (d) are (L,0, 0);
step 6: respectively calculating the three-dimensional coordinates of the imaging points of the target point on two imaging planes according to the internal parameter matrix K, wherein the imaging point g of the target point on the imaging plane C1 1 The three-dimensional coordinates (X, Y,0) of (a) are calculated as follows:
imaging point g of target point on imaging plane C2 2 The three-dimensional coordinates (X ', Y',0) of (a) are calculated as follows:
and 7: using optical centre c 1 Image point g 1 Establish the equation of a straight line L1 using the optical center c 2 An image point g 2 Establishing a linear equation L2, and solving an intersection G of the straight lines L1 and L2 0 Then point of intersection G 0 Coordinate (x) of (2) t ,y t ,z t ) That is, the coordinates of the target point, where the calculated three-dimensional coordinates are respectively expressed as:
wherein F is the focal length of the camera;
and 8: fitting by using a least square method according to the obtained target point coordinates to obtain a spherical equation where the cornea is located;
and step 9: and solving the Gaussian diopter of each target point on the spherical surface to obtain a corneal topography.
2. A corneal topography measuring method according to claim 1, wherein said step 8 comprises:
step 8.1: according to the n target point coordinates { (x) 1 ,y 1 ,z 1 ),(x 2 ,y 2 ,z 2 ),…,(x t ,y t ,z t ),…,(x n ,y n ,z n ) The solution equation for constructing the sphere to be fitted is as follows:
in the formula (I), the compound is shown in the specification,
a matrix of coefficients is represented by a matrix of coefficients,
a representation of the observation vector is shown,
representing parameters to be estimated, t is 1,2, …, n, r represents the radius of the sphere to be fitted, and a, b and c represent the parameters to be estimated of the sphere to be fitted;
step 8.2: converting the formula (4) into U ═ A T A) -1 A T And B, substituting n target point coordinates, solving specific values of a, B, c and r by using a least square method, and determining a determined equation of the spherical surface to be fitted as a spherical surface equation of the cornea.
3. A corneal topography measuring method according to claim 2, wherein said step 9 comprises:
step 9.1: rotating a normal plane of the target point intersected with the spherical surface on the spherical surface by taking the normal as a symmetry axis, calculating curvature radiuses along all tangential directions, taking the maximum curvature and the minimum curvature, and converting the maximum curvature and the minimum curvature into diopter;
step 9.2: calculating the average value of the diopter of the maximum curvature and the diopter of the minimum curvature to obtain Gaussian diopter;
step 9.3: repeating the step 9.1 to the step 9.2, and calculating the Gauss diopter of all the target points;
step 9.4: and (3) carrying out grid division on a data field formed by all Gaussian refraction values, solving the data value of an unknown point by a data field interpolation method, and then carrying out color coding processing to finally form a corneal topography.
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| NL2012004C2 (en) * | 2013-12-20 | 2015-06-26 | Optics B V I | Determining global shape parameters of a cornea using an aspheric toric surface model. |
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| CN102508944A (en) * | 2011-10-10 | 2012-06-20 | 沈阳理工大学 | Corneal surface shape fitting method |
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| CN110974150A (en) * | 2019-12-02 | 2020-04-10 | 四川大学 | Method for measuring human eye cornea topography |
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