A calibration base and calibration system for a handheld corneal topographer

Abstract

The application provides a calibration base and a calibration system for a handheld corneal topographer. The calibration base is assembled by a base surface shell and a base bottom shell into a base body, and a calibration ball and a moving table are embedded on the base body, the calibration ball is carried on the moving table, and the position adjustment of the calibration ball on the X axis, the Y axis or the Z axis is realized by driving the moving table. The calibration system adopts the calibration base, and a handheld corneal topographer is placed on the calibration base, and a PC is electrically connected with the handheld corneal topographer; the calibration system comprises three parts of mechanical alignment, optical calibration and feedback adjustment. The application aims to solve the calibration problem of the handheld corneal topographer and ensure the calibration precision.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ophthalmic medical devices, more particularly to a hand-held corneal topography calibrating base and calibrating system. BACKGROUND

[0002] Using a corneal topography, it has great clinical significance for early screening of ocular corneal diseases in children under 4 years old.

[0003] The traditional fixed corneal topography requires the patient to sit and keep the head fixed, and the cooperation degree of children under 3 years old is low, which easily leads to measurement failure or data distortion; the design of the mandibular support and the forehead support is not suitable for children under 1.2 meters tall, which easily causes deviation in positioning the corneal vertex.

[0004] In order to facilitate the screening of ocular corneal diseases in children under 4 years old, the hand-held corneal topography has been designed and put into the market by the researchers in the field, and at present, there is a lack of effective calibration method or calibration system for the hand-held corneal topography, and the traditional desktop corneal topography calibration system cannot be adapted to the hand-held corneal topography. SUMMARY

[0005] In order to solve the above problems, the present application provides a hand-held corneal topography calibrating base and calibrating system, which aims to solve the calibration problem of the hand-held corneal topography and ensure the calibration accuracy.

[0006] In order to solve the above technical problems, the present application adopts the following technical scheme: a hand-held corneal topography calibrating base, which is assembled by a base surface shell and a base bottom shell into a base body, a calibration ball and a moving table are embedded on the base body, the calibration ball is carried on the moving table, and the position adjustment of the calibration ball on the X-axis, Y-axis or Z-axis is realized by driving the moving table.

[0007] Preferably, the moving table is integrated with an X-axis moving mechanism, a Y-axis moving mechanism and a Z-axis moving mechanism, and the X-axis moving mechanism, the Y-axis moving mechanism and the Z-axis moving mechanism are arranged in space in the order from bottom to top.

[0008] The Z-axis moving mechanism comprises a knob Z, a cam, a thimble, a cover plate and a reset spring Z, wherein the cam is movably mounted on the main body of the Z-axis moving mechanism through a rotating shaft; the knob Z is connected with the main body of the Z-axis moving mechanism in a horizontal direction, the end of the knob Z abuts against one side of the cam, and the other side of the cam abuts against the bottom end of the vertically arranged thimble; the cover plate is arranged above the cam and is used for bearing the calibration ball, the top of the thimble is fixedly embedded in the cover plate; the reset spring Z is vertically arranged, the upper end of the reset spring Z is connected with the cover plate, and the lower end of the reset spring Z is connected with the main body of the Z-axis moving mechanism; the knob Z is rotated in or out to drive the cam to rotate around the rotating shaft, and then drive the thimble to carry the cover plate to move along the Z-axis direction.

[0009] The Y-axis moving mechanism is fixedly connected with the main body of the Z-axis moving mechanism above, and is slidably connected with the main body of the X-axis moving mechanism through a Y-direction sliding rail below, a reset spring Y is arranged at the sliding connection, the arrangement direction of the reset spring Y is consistent with the Y-direction sliding rail, one end of the reset spring Y is connected with the main body of the Y-axis moving mechanism, and the other end of the reset spring Y is connected with the main body of the X-axis moving mechanism; a knob Y is connected with the main body of the Y-axis moving mechanism along the arrangement direction of the Y-direction sliding rail, the knob Y is rotated in or out to drive the main body of the Y-axis moving mechanism and the main body of the Z-axis moving mechanism to move along the Y-axis direction.

[0010] The X-axis moving mechanism is fixedly connected with the main body of the Y-axis moving mechanism above, and is slidably connected with the base of the moving table through an X-direction sliding rail below, a reset spring X is arranged at the sliding connection, the arrangement direction of the reset spring X is consistent with the X-direction sliding rail, one end of the reset spring X is connected with the main body of the X-axis moving mechanism, and the other end of the reset spring X is connected with the base of the moving table; a knob X is connected with the main body of the X-axis moving mechanism along the arrangement direction of the X-direction sliding rail, the knob X is rotated in or out to drive the main body of the X-axis moving mechanism, the main body of the Y-axis moving mechanism and the main body of the Z-axis moving mechanism as a whole to move along the X-axis direction.

[0011] Preferably, the moving table is fixedly connected with the aluminum alloy plate below in a screw connection mode.

[0012] Preferably, the base surface shell is provided with an anti-collision structure in the form of a mushroom head structure which is sequentially assembled and connected by an anti-collision pad A, an anti-collision pad B, an anti-collision pad C and an anti-collision pad D.

[0013] Preferably, the bottom surface of the base bottom shell is provided with an anti-skid pad.

[0014] Preferably, the calibration ball is an integrated structure with a hemispherical upper part and a cylindrical lower part.

[0015] The utility model relates to a kind of calibration system for handheld corneal topographer, using the calibration base of the utility model, handheld corneal topographer is placed on calibration base, PC machine is electrically connected with handheld corneal topographer;The calibration system includes three parts of mechanical alignment, optical calibration and feedback adjustment, wherein,

[0016] (1) mechanical calibration: handheld corneal topographer is placed on calibration base, keep the main camera of handheld corneal topographer face standard base on calibration ball, calibration ball is supported on the moving table arranged inside calibration base, by driving moving table along X axis, Y axis moves, make the central axis of the main camera of handheld corneal topographer with calibration ball center alignment, by driving moving table along Z axis moves, make the main camera in handheld corneal topographer get clear image, to realize mechanical alignment;

[0017] (2) optical calibration: PC machine is electrically connected with handheld corneal topographer;In the case where moving table Z axis is fixed, use the main camera of handheld corneal topographer to take multiple photos to calibration ball, PC machine obtains actual optical center point OAP according to multiple images obtained by shooting;In the case where moving table X axis and Y axis are fixed, use the side lens of handheld corneal topographer to take multiple photos to calibration ball, PC machine obtains the distance between actual corneal vertex and CMOS chip in the main camera of handheld corneal topographer according to multiple images obtained by shooting;

[0018] (3) feedback adjustment: compare actual optical center point OAP with theoretical optical center point OAP, obtain optical center point OAP correction parameter;Compare the distance between actual corneal vertex and CMOS chip in the main camera of handheld corneal topographer with the distance between theoretical corneal vertex and CMOS chip in the main camera of handheld corneal topographer, obtain corneal vertex distance parameter;The above optical center point OAP correction parameter and corneal vertex distance parameter are fed back to PC machine, PC machine is adaptively adjusted, and the position of actual optical center point OAP is corrected to the position of theoretical optical center point OAP, and the distance between actual corneal vertex and CMOS chip in the main camera of handheld corneal topographer is adjusted to the distance between theoretical corneal vertex and CMOS chip in the main camera of handheld corneal topographer.

[0019] The acquisition method of the actual optical center point OAP is,

[0020] S101, calibration ball is photographed by main camera, and original image is obtained:

[0021] (1) positioned in (x1, y1) coordinate, the first image of calibration ball is shot, and ensure that topographic ring is in focus;

[0022] (2) Keep the Z-axis fixed and take a second image at the (x2, y2) coordinate position;

[0023] (3) Keep the Z-axis fixed and take a third image at the (x3, y3) coordinate position;

[0024] S102, Image Enhancement;

[0025] S103, Locate the center point of the innermost ring;

[0026] S104. Analyze the image and obtain the corresponding points, M rings, N points per ring;

[0027] S105. Calculate the optimal centroids of M fitted circles / ellipses;

[0028] S106. Find the best straight line that fits the center points of M rings;

[0029] S107. Based on images at three different (x, y) coordinate positions, extrapolate three best-fit lines;

[0030] S108. Calculate the intersection points of the three best-fit lines with other lines to form a triangle;

[0031] S109. Calculate the centroid of the triangle as the actual optical center point OAP.

[0032] The method for obtaining the distance between the actual corneal vertex and the CMOS chip inside the main camera of the handheld corneal topography instrument is as follows:

[0033] S201. Take pictures of the calibration ball using the main camera and side cameras to obtain the original images:

[0034] (1) Keep the X-axis and Y-axis fixed, and take the first image of the calibration ball at the optical axis of the corneal topography instrument and in the Z-axis direction by setting a distance A;

[0035] (2) In the Z-axis direction, take a second image at a set distance B, where B > A;

[0036] (3) In the Z-axis direction, take a third image at a set distance C, where C > B;

[0037] S202. The obtained side camera image is cropped and preprocessed. Then, the U-Net model is used to locate the corneal vertex and obtain the distance between the corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument to obtain distance information.

[0038] S203, the obtained main camera image is image enhanced, and the center point of the innermost ring is positioned; the image is analyzed and the corresponding point position is obtained, M ring, N points per ring; the average curvature value of each ring is obtained; according to the distance information obtained in S202, the aspherical surface value corresponding to the distance is obtained;

[0039] S204, based on the images of more than three different distances, a distance adjustment model is established by linear regression, and the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument is obtained.

[0040] The application solves the industry pain points of low calibration accuracy, complex operation and poor environmental adaptability of handheld corneal topography instrument, realizes the calibration target of high precision, high efficiency and high reliability, and the specific technical effects are shown in the following aspects:

[0041] 1, X / Y / Z axis independent control, cam-pin transmission, slide rail guide and spring reset structure are adopted, so that the axial displacement accuracy can reach micron level (±10um), which meets the high-precision calibration requirement of corneal topography instrument on optical center (OAP) and corneal vertex distance;

[0042] 2, from bottom to top, the layered structure (X→Y→Z) is adopted, the mechanical coupling error during multi-axis movement is avoided through the physical isolation design of slide rail and reset spring, and the stability of independent adjustment of each axis is ensured;

[0043] 3, the calibration ball structure of hemisphere + cylinder simulates the curvature of human cornea, combined with the multi-ring image analysis algorithm, the influence of optical distortion on positioning accuracy is reduced, and the positioning error of optical center point OAP is less than or equal to 0.1mm;

[0044] 4, through image acquisition at three different positions, combined with ring fitting, linear extrapolation and triangle centroid algorithm, the optical center point calibration time is greatly shortened;

[0045] 5, the side camera image is segmented by the pre-trained U-Net model in real time, the positioning accuracy reaches pixel level (error ≤5um), and the subjectivity of manual interpretation is avoided;

[0046] 6, based on the curvature data of multiple distances (A BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 Exploded view of base.

[0048] Figure 2 Planer view of base.

[0049] Figure 3 Perspective view of base.

[0050] Figure 4 Exploded view of the structure where the calibration ball is stored.

[0051] Figure 5 A spherical section diagram of the calibration storage structure.

[0052] Figure 6 A three-dimensional view of the structure for storing calibration balls.

[0053] Figure 7 Moving table planing Figure 1 .

[0054] Figure 8 Moving table planing Figure 2 .

[0055] Figure 9 3D view of the mobile station.

[0056] Among them: Anti-collision pad A1, Anti-collision pad B2, Anti-collision pad C3, Anti-collision pad D4, Base shell 5, Moving platform 6, Aluminum alloy plate 7, Base bottom shell 8, Anti-slip pad 9, Silicone sleeve 10, Calibration ball inner support plate 11, Calibration ball 12, Calibration ball fixing piece 13, Calibration ball inner support 14, Calibration ball packaging box 15, Knob X16, Return spring X17, X-direction slide rail 18-2, Y-direction slide rail 18-1, Return spring Y19, Knob Z20, Cam 21, Ejector pin 22, Cover plate 23, Return spring Z24, Knob Y25. Detailed Implementation

[0057] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0058] like Figures 1 to 3 The calibration base for a handheld corneal topography instrument shown is assembled from a base shell 5 and a base bottom shell 8 to form a base body. A calibration ball 12 and a moving stage 6 are embedded in the base body. The calibration ball 12 is supported on the moving stage 6. By driving the moving stage 6, the position of the calibration ball 12 on the X-axis, Y-axis or Z-axis can be adjusted.

[0059] like Figures 7 to 9 As shown, the moving stage 6 integrates an X-axis moving mechanism, a Y-axis moving mechanism, and a Z-axis moving mechanism. The X-axis moving mechanism, the Y-axis moving mechanism, and the Z-axis moving mechanism are stacked in space from bottom to top (X→Y→Z) to avoid motion interference and ensure the independence of each axis.

[0060] The Z-axis moving mechanism comprises a knob Z20, a cam 21, a thimble 22, a cover plate 23 and a reset spring Z24, wherein the cam 21 is movably mounted on the main body of the Z-axis moving mechanism through a rotating shaft; the knob Z20 is connected with the main body of the Z-axis moving mechanism in a horizontal direction, the end of the knob Z20 abuts against one side of the cam 21, and the other side of the cam 21 abuts against the bottom end of the vertically arranged thimble 22; the cover plate 23 is arranged above the cam 21 and is used for bearing the calibration ball 12, the top of the thimble 22 is fixedly embedded in the cover plate 23; the reset spring Z24 is vertically arranged, the upper end of the reset spring Z24 is connected with the cover plate 23, and the lower end of the reset spring Z24 is connected with the main body of the Z-axis moving mechanism; the knob Z20 is rotated in or out to drive the cam 21 to rotate around the rotating shaft, and then drive the thimble 22 to carry the cover plate 23 to move along the Z-axis direction; the reset spring Z24 ensures reverse reset, and micron-level Z-direction adjustment is realized.

[0061] The Y-axis moving mechanism is fixedly connected with the main body of the Z-axis moving mechanism above, and is slidably connected with the main body of the X-axis moving mechanism through a Y-direction sliding rail 18-1 below, a reset spring Y19 is arranged at the sliding connection position, the arrangement direction of the reset spring Y19 is consistent with the arrangement direction of the Y-direction sliding rail 18-1, one end of the reset spring Y19 is connected with the main body of the Y-axis moving mechanism, and the other end of the reset spring Y19 is connected with the main body of the X-axis moving mechanism; along the arrangement direction of the Y-direction sliding rail 18-1, a knob Y25 is connected with the main body of the Y-axis moving mechanism, the knob Y25 is rotated in or out to drive the main body of the Y-axis moving mechanism and the main body of the Z-axis moving mechanism to move along the Y-axis direction; the reset spring Y19 provides a reset force to drive the Z-axis mechanism to move along the Y-axis

[0062] The X-axis moving mechanism is fixedly connected with the main body of the Y-axis moving mechanism above, and is slidably connected with the base of the moving table 6 through an X-direction sliding rail 18-2 below, a reset spring X17 is arranged at the sliding connection position, the arrangement direction of the reset spring X17 is consistent with the arrangement direction of the X-direction sliding rail 18-2, one end of the reset spring X17 is connected with the main body of the X-axis moving mechanism, and the other end of the reset spring X17 is connected with the base of the moving table 6; along the arrangement direction of the X-direction sliding rail 18-2, a knob X16 is connected with the main body of the X-axis moving mechanism, the knob X16 is rotated in or out to drive the main body of the X-axis moving mechanism, the main body of the Y-axis moving mechanism and the main body of the Z-axis moving mechanism to move along the X-axis direction; the reset spring X17 resets to drive the Y-axis and the Z-axis to move along the X-axis.

[0063] The moving table 6 is fixedly connected with the aluminum alloy plate 7 below in a screw connection mode, and light weight and rigidity are considered.

[0064] The anti-collision structure is a mushroom head structure sequentially assembled by the anti-collision pad A1, the anti-collision pad B2, the anti-collision pad C3 and the anti-collision pad D4, and the mushroom head type anti-collision pad structure design can effectively disperse impact force and protect precise components.

[0065] The bottom surface of the base bottom shell 8 is provided with the anti-skid pad 9, which effectively prevents sliding.

[0066] As shown in the figure, Figure 4 The calibration ball 12 is an integrated structure with a semispherical upper part and a cylindrical lower part, the semispherical upper part simulates corneal curvature for facilitating optical positioning, and the cylindrical lower part ensures stable bearing.

[0067] The calibration system for the handheld corneal topographer adopts the calibration base, places the handheld corneal topographer on the calibration base, and electrically connects the PC and the handheld corneal topographer, and the calibration system comprises mechanical alignment, optical calibration and feedback adjustment.

[0068] Mechanical calibration: the handheld corneal topographer is placed on the calibration base, the main camera of the handheld corneal topographer is kept facing the calibration ball 12 on the standard base, the calibration ball 12 is borne on the moving table 6 arranged inside the calibration base, the moving table 6 is driven to move along the X axis and the Y axis, so that the central axis of the main camera of the handheld corneal topographer is aligned with the center of the calibration ball 12, the moving table 6 is driven to move along the Z axis, so that the main camera in the handheld corneal topographer obtains a clear image, thereby realizing mechanical alignment.

[0069] Optical calibration: the PC and the handheld corneal topographer are electrically connected, the calibration ball 12 is photographed multiple times by the main camera of the handheld corneal topographer under the condition that the moving table 6 Z axis is fixed, the PC analyzes and calculates the actual optical center point OAP according to the multiple images obtained by photographing, the calibration ball 12 is photographed multiple times by the side lens of the handheld corneal topographer under the condition that the moving table 6 X axis and the moving table 6 Y axis are fixed, and the PC analyzes and calculates the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topographer according to the multiple images obtained by photographing.

[0070] The method for obtaining the actual optical center point OAP is specifically,

[0071] S101, the calibration ball 12 is photographed by the main camera to obtain an original image:

[0072] (1) positioned at the (x1, y1) coordinate, the first image of the calibration ball 12 is photographed, and the topographic ring is ensured to be in clear focus;

[0073] (2) keep the Z axis unchanged, take the second image at the (x2, y2) coordinate position;

[0074] (3) continue to keep the Z axis unchanged, take the third image at the (x3, y3) coordinate position;

[0075] S102, image enhancement, remove noise using Gaussian filter, and enhance the contrast of the topographic ring using CLAHE algorithm; S103, extract the topographic ring (such as Placido ring) on the calibration ball surface in each image, and locate the center point of the innermost ring;

[0076] S104, analyze the image and obtain the corresponding point position, M rings, N points per ring;

[0077] S105, calculate the best centroid of M fitted circles / ellipses;

[0078] S106, fit the best straight line of M ring center points;

[0079] S107, extrapolate three best fitting straight lines based on three images with different (x, y) coordinate positions;

[0080] S108, calculate the intersection of the three best fitting straight lines and other straight lines to form a triangle;

[0081] S109, calculate the centroid of the triangle as the actual optical center point OAP.

[0082] The specific method for obtaining the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topographer is as follows:

[0083] S201, take the calibration ball 12 through the main camera and the side camera to obtain the original image:

[0084] (1) keep the X axis and Y axis fixed, at the corneal topographer optical axis positioning position and in the Z axis direction, take the first image of the calibration ball 12 by setting the distance A;

[0085] (2) in the Z axis direction, take the second image by setting the distance B, B > A;

[0086] (3) in the Z axis direction, take the third image by setting the distance C, C > B;

[0087] S202, crop the calibration ball region in the side camera image, input the pre-trained U-Net model, segment out the corneal vertex coordinates, obtain the distance between the corneal vertex and the CMOS chip in the main camera of the handheld corneal topographer, and obtain the distance information;

[0088] S203, the obtained main camera image is image enhanced, and the center point of the innermost ring is positioned; the image is analyzed and the corresponding point position is obtained, M rings, N points per ring; the average curvature value of each ring is obtained; the curvature data (such as ring spacing change) of the calibration ball in the main camera image is extracted, combined with the Z-axis displacement amount, a distance-curvature linear regression model is established; the actual corneal vertex and the theoretical distance of the CMOS chip are back calculated through the model.

[0089] Feedback adjustment: compare the actual optical center point OAP with the theoretical optical center point OAP to obtain the optical center point OAP correction parameter; compare the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument with the distance between the theoretical corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument to obtain the corneal vertex distance parameter; the above optical center point OAP correction parameter and corneal vertex distance parameter are fed back to the PC, and the PC is adaptively adjusted to correct the position of the actual optical center point OAP to the position of the theoretical optical center point OAP, and adjust the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument to the distance between the theoretical corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument.

Claims

1. A calibration stand for a handheld corneal topographer, characterized by: The base body is assembled by the base surface shell (5) and the base bottom shell (8), the calibration ball (12) and the moving table (6) are embedded on the base body, the calibration ball (12) is carried on the moving table (6), the position adjustment of the calibration ball (12) on the X axis, the Y axis or the Z axis is realized by driving the moving table (6); The moving table (6) is integrated with the X-axis moving mechanism, the Y-axis moving mechanism and the Z-axis moving mechanism, and the X-axis moving mechanism, the Y-axis moving mechanism and the Z-axis moving mechanism are arranged in the space in the order from bottom to top; The Z-axis moving mechanism comprises a knob Z (20), a cam (21), a thimble (22), a cover plate (23) and a reset spring Z (24), wherein the cam (21) is movably mounted on the main body of the Z-axis moving mechanism through a rotating shaft; the knob Z (20) is connected with the main body of the Z-axis moving mechanism in the horizontal direction, the end of the knob Z (20) abuts against one side of the cam (21), and the other side of the cam (21) abuts against the bottom of the vertically arranged thimble (22); the cover plate (23) is located above the cam (21) and is used for carrying the calibration ball (12), the top of the thimble (22) is fixedly embedded in the cover plate (23); the reset spring Z (24) is vertically arranged, the upper end of the reset spring Z (24) is connected with the cover plate (23), and the lower end of the reset spring Z (24) is connected with the main body of the Z-axis moving mechanism; the knob Z (20) is rotated in or out, the cam (21) is driven to rotate around the rotating shaft, and then the thimble (22) carries the cover plate (23) to move along the Z-axis direction; The Y-axis moving mechanism is fixedly connected with the main body of the Z-axis moving mechanism above, and is slidably connected with the main body of the X-axis moving mechanism through a Y-direction sliding rail (18-1) below, a reset spring Y (19) is arranged at the sliding connection position, the arrangement direction of the reset spring Y (19) is consistent with the arrangement direction of the Y-direction sliding rail (18-1), one end of the reset spring Y (19) is connected with the main body of the Y-axis moving mechanism, and the other end of the reset spring Y (19) is connected with the main body of the X-axis moving mechanism; along the arrangement direction of the Y-direction sliding rail (18-1), a knob Y (25) is connected with the main body of the Y-axis moving mechanism, the knob Y (25) is rotated in or out, and the main body of the Y-axis moving mechanism and the main body of the Z-axis moving mechanism are driven to move along the Y-axis direction; The X-axis moving mechanism is fixedly connected with the main body of the Y-axis moving mechanism at the top, and is slidably connected with the base of the moving table (6) at the bottom through an X-direction sliding rail (18-2). A reset spring X (17) is arranged at the sliding connection position, and the arrangement direction of the reset spring X (17) is consistent with the X-direction sliding rail (18-2). One end of the reset spring X (17) is connected with the main body of the X-axis moving mechanism, and the other end of the reset spring X (17) is connected with the base of the moving table (6). A knob X (16) is arranged on the X-direction sliding rail (18-2) and connected with the main body of the X-axis moving mechanism. By rotating the knob X (16) in or out, the main bodies of the X-axis moving mechanism, the Y-axis moving mechanism and the Z-axis moving mechanism are driven to move along the X-axis direction.

2. A calibration stand for a handheld corneal topographer according to claim 1, characterized in that: The moving table (6) is fixedly connected with the aluminum alloy plate (7) below by means of screw connection.

3. A calibration stand for a hand-held corneal topographer according to claim 1, characterized in that: The base surface shell (5) is provided with an anti-collision structure which is a mushroom head structure formed by sequentially assembling anti-collision pads A (1), B (2), C (3) and D (4).

4. A calibration stand for a hand-held corneal topographer according to claim 1, characterized in that: The bottom surface of the base bottom shell (8) is provided with an anti-skid pad (9).

5. A calibration stand for a hand-held corneal topographer according to claim 1, characterized in that: The calibration ball (12) is an integrated structure with a hemispherical upper part and a cylindrical lower part.

6. A calibration system for a handheld corneal topographer, employing a calibration base as claimed in any one of claims 1 to 5, characterized in that: The handheld corneal topographer is placed on the calibration base, and the PC is electrically connected with the handheld corneal topographer; the calibration system comprises mechanical alignment, optical calibration and feedback adjustment three parts, wherein, (1) mechanical calibration: the handheld corneal topographer is placed on the calibration base, and the main camera of the handheld corneal topographer is kept facing the calibration ball (12) on the calibration base. The calibration ball (12) is borne on the moving table (6) arranged inside the calibration base. The moving table (6) is driven to move along the X-axis and the Y-axis, so that the central axis of the main camera of the handheld corneal topographer is aligned with the center of the calibration ball (12). The moving table (6) is driven to move along the Z-axis, so that the main camera of the handheld corneal topographer obtains a clear image, thereby realizing mechanical alignment; (2) optical calibration: the PC is electrically connected with the handheld corneal topographer. In the case that the Z-axis of the moving table (6) is fixed, the main camera of the handheld corneal topographer is used to take multiple pictures of the calibration ball (12). The PC analyzes and calculates the actual optical center point OCP according to the multiple images obtained by shooting. In the case that the X-axis and the Y-axis of the moving table (6) are fixed, the side lens of the handheld corneal topographer is used to take multiple pictures of the calibration ball (12). The PC analyzes and calculates the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topographer according to the multiple images obtained by shooting. (3) Feedback adjustment: compare the actual optical center point OCP with the theoretical optical center point OCP to obtain an optical center point OCP correction parameter; compare the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument with the distance between the theoretical corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument to obtain a corneal vertex distance parameter; feed the optical center point OCP correction parameter and the corneal vertex distance parameter to the PC, and the PC adjusts and corrects the position of the actual optical center point OCP to the position of the theoretical optical center point OCP and adjusts the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument to the distance between the theoretical corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument.

7. The calibration system for a handheld videokeratograph according to claim 6, characterized in that: The method for obtaining the actual optical center point OCP is, S101, capture the calibration ball (12) through the main camera to obtain an original image: (1) position at (x1, y1) coordinates, capture the first image of the calibration ball (12), and ensure that the topographic ring is in clear focus; (2) keep the Z axis fixed, capture the second image at (x2, y2) coordinates; (3) continue to keep the Z axis fixed, capture the third image at (x3, y3) coordinates; S102, image enhancement; S103, locate the center point of the innermost ring; S104, analyze the image and obtain the corresponding point position, M rings, and N points per ring; S105, calculate the best centroid of M fitted circles or ellipses; S106, fit the best straight line of M ring center points; S107, extrapolate three best fitting straight lines based on images at three different (x, y) coordinate positions; S108, calculate the intersection of the three best fitting straight lines and other straight lines to form a triangle; S109, calculate the centroid of the triangle as the actual optical center point OCP.

8. The calibration system for a handheld videokeratograph according to claim 6, characterized in that: The method for obtaining the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument is, S201, capture the calibration ball (12) through the main camera and the side camera to obtain an original image: (1) keep the X axis and Y axis fixed, position at the corneal topography instrument optical axis and in the Z axis direction, capture the first image of the calibration ball (12) by setting a distance A; (2) in the Z axis direction, capture the second image by setting a distance B, B>A; (3) in the Z axis direction, capture the third image by setting a distance C, C>B; S202, crop and image pretreat the obtained side camera image, then locate the corneal vertex by using a U-Net model to obtain the distance between the corneal vertex and the CMOS chip in the main camera of the handheld corneal topography instrument, and obtain distance information; S203, image enhance the obtained main camera image, locate the center point of the innermost ring, analyze the image and obtain the corresponding point position, M rings, and N points per ring, and obtain the average curvature value of each ring; According to the distance information obtained in S202, obtain the aspherical surface value corresponding to the distance; S204, based on ≥3 different distance images, a linear regression is used to establish a distance adjustment model to obtain the distance between the actual corneal vertex and the CMOS chip in the main camera of the handheld corneal topography.

Images