Measurement method and system of non-contact intraocular pressure instrument and non-contact intraocular pressure instrument

Abstract

The invention provides a measuring method of a non-contact intraocular pressure instrument and the non-contact intraocular pressure instrument. The measuring method of the non-contact intraocular pressure instrument comprises the following steps: acquiring a first human eye image in the XY direction and a second human eye image in the Z direction of an examined eye; identifying the first human eye image according to a pupil identification method and a positioning light spot detection method to determine the pupil of the detected eye and the mass center of the pupil contour; identifying a cornea bright line of the second human eye image according to a cornea bright line detection method so as to determine a cornea vertex of the detected eye; performing XY-direction positioning adjustment based on the pupil and the center of mass of the pupil contour, and performing Z-direction positioning adjustment based on the cornea vertex and the calibration point in the Z direction; in response to the completion of the XY-direction positioning adjustment and the Z-direction positioning adjustment, blowing air to the examined eye to obtain a cornea deformation image shot by the high-speed camera sensor; and determining the intraocular pressure value of the examined eye based on the cornea thickness and the cornea curvature determined by the cornea deformation image and the pressure change curve of the blowing air cavity.

Description

Technical Field

[0001] The present invention relates to an ophthalmic measuring instrument, and in particular to a measuring method of a non-contact tonometer, a measuring system of a non-contact tonometer, a non-contact tonometer, and a computer-readable storage medium. Background Art

[0002] Glaucoma is one of the three major eye diseases that cause blindness in humans. It refers to an eye disease in which the intraocular pressure increases intermittently or continuously. Continuous high intraocular pressure can cause damage to various tissues and visual functions of the eyeball. If not treated in time, the visual field may be completely lost, leading to blindness.

[0003] Intraocular pressure detection is an effective way to diagnose glaucoma. In the prior art, non-contact tonometers project air onto the eye along the direction of the optical axis so that the cornea gradually flattens and eventually sinks. During the corneal deformation process, a beam of parallel light is incident obliquely on the cornea, and the amount of light reflected back from the cornea is measured to achieve the measurement of corneal deformation. The intraocular pressure value is then calculated in combination with the air blowing pressure. However, the existing intraocular pressure measurement method does not take into account the back pressure caused by the elastic deformation of the cornea. When measuring intraocular pressure, a certain force is required to deform the cornea. Since the cornea itself is an elastic membrane, the back pressure caused by this deformation is also included in the measurement result of the corneal deformation. Therefore, the existing non-contact tonometer has low measurement accuracy.

[0004] In order to overcome the above-mentioned defects of the prior art, there is an urgent need in the art for a non-contact tonometer and a measurement technology of the non-contact tonometer, which can improve the measurement accuracy of intraocular pressure. Summary of the invention

[0005] A brief summary of one or more aspects is given below to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceived aspects, and is neither intended to identify the key or critical elements of all aspects nor to define the scope of any or all aspects. Its only purpose is to give some concepts of one or more aspects in a simplified form as a prelude to a more detailed description that will be given later.

[0006] In order to overcome the above-mentioned defects in the prior art, the present invention provides a measurement method of a non-contact tonometer, a measurement system of a non-contact tonometer, a non-contact tonometer, and a computer-readable storage medium, which can improve the measurement accuracy of intraocular pressure.

[0007] Specifically, the measurement method of the above-mentioned non-contact tonometer provided according to the first aspect of the present invention includes the steps of: acquiring a first human eye image in the XY direction and a second human eye image in the Z direction of the eye to be inspected; identifying the first human eye image according to a pupil recognition method and a positioning light point detection method to determine the pupil of the eye to be inspected and the center of mass of the pupil contour; identifying the corneal bright line of the second human eye image according to a corneal bright line detection method to determine the corneal vertex of the eye to be inspected; performing XY direction positioning adjustment based on the center of mass of the pupil and the pupil contour, and performing Z direction positioning adjustment based on the corneal vertex and the calibration point in the Z direction; in response to the completion of the XY direction positioning adjustment and the Z direction positioning adjustment, blowing air into the eye to be inspected to obtain a corneal deformation image during the blowing process captured by a high-speed camera sensor; and determining the intraocular pressure value of the eye to be inspected based on the corneal thickness and corneal curvature determined by the corneal deformation image and the pressure change curve of the blowing air cavity.

[0008] Preferably, in one embodiment of the present invention, the step of identifying the first human eye image according to the pupil recognition method and the positioning light spot detection method to determine the pupil of the eye to be inspected and the centroid of the pupil contour includes: performing edge detection on the first human eye image to determine pupil contour candidates; determining the approximate dominant points of the pupil contour candidates by the k-cosine chain approximation method; calculating the approximate dominant points of the pupil contour candidates by heuristic rules to exclude error terms in the pupil contour candidates; calculating the pupil confidence of the remaining pupil contour candidates, and determining the pupil of the eye to be inspected based on the pupil confidence; and based on the pupil, performing binarization processing, contour detection, ellipse fitting and centroid search on the first human eye image to determine the centroid of the pupil contour.

[0009] Preferably, in one embodiment of the present invention, the corneal bright line detection method comprises the steps of: performing contour detection and contour merging on the second human eye image to determine the corneal bright line.

[0010] Preferably, in one embodiment of the present invention, the step of performing contour detection and contour merging on the second human eye image to determine the corneal bright line includes: performing edge detection on the second human eye image based on the Canny algorithm to determine the edge contour; performing neighboring point search on the contour points of the edge contour through a spatial index accelerator; merging the contour points and the neighboring points to obtain a neighboring contour; merging the neighboring contours within a distance threshold to obtain a merged contour; and based on the span of the X-axis, determining the merged contour with the largest span as the corneal bright line.

[0011] In addition, the measurement system of the non-contact tonometer provided according to the second aspect of the present invention includes a memory and a processor. The memory stores computer instructions. The processor is connected to the memory and is configured to execute the computer instructions stored in the memory to implement the measurement method of the non-contact tonometer provided in any one of the above embodiments.

[0012] In addition, the above-mentioned non-contact tonometer provided according to the third aspect of the present invention includes an air blowing device, a slit light source system and a fixation optical system, and also includes: a positioning system, the positioning system includes an XY direction positioning module and a Z direction positioning module, the XY direction positioning module and the Z direction positioning module respectively include a projection unit and a light receiving unit; a high-speed camera shooting system, used to record the corneal deformation image during the corneal deformation process; and the measurement system of the above-mentioned non-contact tonometer provided by the second aspect of the present invention.

[0013] Preferably, in an embodiment of the present invention, the XY direction positioning module and the Z direction positioning module include a projection unit and a light receiving unit respectively.

[0014] Preferably, in one embodiment of the present invention, the projection unit of the XY direction positioning module includes multiple groups of light sources, aperture holes and lenses, and the multiple groups of light sources, aperture holes and lenses are fixed symmetrically along the axis in a circular surround form, so as to form a projection spot on the cornea of ​​the eye to be inspected; and the light receiving unit includes a lens group and an image sensor.

[0015] Preferably, in one embodiment of the present invention, the projection unit of the Z-direction positioning module is shared with the slit light source system, and the light receiving unit is shared with the high-speed camera shooting system.

[0016] Preferably, in one embodiment of the present invention, the high-speed camera shooting system includes a lens group and a high-speed camera sensor, the lens group is located in the main plane, the cornea of ​​the eye to be inspected is located in the tangent plane, and the receiving surface of the high-speed camera sensor is arranged based on Schaam's law.

[0017] In addition, the computer-readable storage medium provided according to the fourth aspect of the present invention stores computer instructions, which, when executed by a processor, implement the measurement method of the non-contact tonometer provided by the first aspect of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above features and advantages of the present invention can be better understood after reading the detailed description of the embodiments of the present disclosure in conjunction with the following drawings. In the drawings, the components are not necessarily drawn to scale, and components with similar related properties or features may have the same or similar reference numerals.

[0019] Figure 1 A schematic diagram showing a measurement system of a non-contact tonometer according to some embodiments of the present invention is shown; Figure 2 A plan view schematic diagram of an optical system of a non-contact tonometer 200 provided according to some embodiments of the present invention is shown; Figure 3 A side schematic diagram of an optical system of a non-contact tonometer 200 provided according to some embodiments of the present invention is shown; Figure 4 A schematic diagram showing the position of a projection unit 250 of an XY direction positioning module of a non-contact tonometer 200 provided according to some embodiments of the present invention; Figure 5 A flow chart showing a method for measuring a non-contact tonometer according to some embodiments of the present invention; and Figure 6 A schematic diagram of a second human eye image provided according to some embodiments of the present invention is shown.

[0020] Reference numerals: 100: Measurement system of non-contact tonometer; 110: memory; 111: Computer readable storage medium; 120: Processor; 200: Non-contact tonometer; 201: Reflector; 210: blowing device; 211: Inflating device; 212: air cavity; 213: Nozzle; 220: Slit light source system; 221: Light source; 222: Condenser; 223: aperture; 224: lens group; 225: Reflector; 226: chamber plane mirror; 227: chamber plane mirror; 230: High-speed camera shooting system; 231: lens group; 232: High-speed camera sensor; 240: fixation optical system; 241: Light source; 242: aperture hole; 243: Lens; 250: projection unit of XY direction positioning module; 251: Light source; 252: aperture hole; 253: Lens; 260: light receiving unit of the XY direction positioning module; 261: lens group; 262: Image sensor; 500: Measurement method of non-contact tonometer; E: measurement location; and S510~S560: steps. DETAILED DESCRIPTION

[0021] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Note that the aspects described below in conjunction with the accompanying drawings and specific embodiments are only exemplary and should not be construed as limiting the scope of protection of the present invention in any way.

[0022] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] In addition, the terms "upper", "lower", "left", "right", "top", "bottom", "horizontal" and "vertical" used in the following description should be understood as the directions shown in the paragraph and the related drawings. Such relative terms are only used for the convenience of description and do not mean that the device described therein must be manufactured or operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0024] It is understood that although the terms "first", "second", "third", etc. may be used herein to describe various components, regions, layers and / or parts, these components, regions, layers and / or parts should not be limited by these terms, and these terms are only used to distinguish different components, regions, layers and / or parts. Therefore, the first component, region, layer and / or part discussed below may be referred to as a second component, region, layer and / or part without departing from some embodiments of the present invention.

[0025] As mentioned above, intraocular pressure detection is an effective way to diagnose glaucoma. In the prior art, the non-contact tonometer projects air onto the eye along the direction of the optical axis so that the cornea gradually flattens and eventually sinks. During the corneal deformation process, a beam of parallel light is incident obliquely on the cornea, and the amount of light reflected back from the cornea is measured to achieve the measurement of corneal deformation. The intraocular pressure value is then calculated in combination with the air blowing pressure. However, the existing intraocular pressure measurement method does not take into account the back pressure caused by the elastic deformation of the cornea. When measuring intraocular pressure, a certain force is required to deform the cornea. Since the cornea itself is an elastic membrane, the back pressure caused by this deformation is also included in the measurement result of the corneal deformation. Therefore, the existing non-contact tonometer has low measurement accuracy.

[0026] In order to overcome the above-mentioned defects in the prior art, the present invention provides a measurement method of a non-contact tonometer, a measurement system of a non-contact tonometer, a non-contact tonometer, and a computer-readable storage medium, which can improve the measurement accuracy of intraocular pressure.

[0027] In some non-limiting embodiments, the measurement method of the non-contact tonometer provided in the first aspect of the present invention may be implemented via the measurement system of the non-contact tonometer provided in the second aspect of the present invention.

[0028] Please refer to Figure 1 , Figure 1 A schematic diagram of a measurement system of a non-contact tonometer provided according to some embodiments of the present invention is shown.

[0029] like Figure 1 As shown, the measurement system 100 of the non-contact tonometer may be configured with a memory 110 and a processor 120. The memory 110 includes but is not limited to the computer-readable storage medium 111 provided in the fourth aspect of the present invention, on which computer instructions are stored. The processor 120 is connected to the memory 110 and is configured to execute the computer instructions stored in the memory 110 to implement the measurement method of the non-contact tonometer provided in the first aspect of the present invention.

[0030] In some embodiments, the measurement system of the non-contact tonometer can be configured in the non-contact tonometer to implement the measurement method of the non-contact tonometer provided by the first aspect of the present invention through the non-contact tonometer.

[0031] The non-contact tonometer may include an air blowing device for blowing air to the cornea of ​​the eye to be inspected to deform the cornea, a slit light source system for projecting slit light to the eye to be inspected, a fixation optical system for enabling the eye to be inspected to perform reference positioning by itself, a positioning system, a high-speed camera shooting system, and a measurement system of the non-contact tonometer. The positioning system may include an XY direction positioning module for performing XY positioning of the eye to be inspected and a Z direction positioning module for performing Z positioning of the eye to be inspected, and the high-speed camera shooting system may be used to record corneal section images during corneal deformation.

[0032] Please refer to Figure 2 and Figure 3 , Figure 2 FIG. 2 shows a planar schematic diagram of an optical system of a non-contact tonometer 200 provided according to some embodiments of the present invention. Figure 3 A side schematic diagram of an optical system of a non-contact tonometer 200 provided according to some embodiments of the present invention is shown.

[0033] like Figure 2 As shown, the subject needs to place the eye to be examined at the measurement position E, and the non-contact tonometer 200 may include an air blowing device 210 for blowing air toward the cornea of ​​the eye to be examined to deform the cornea and a slit light source system 220 for projecting slit light toward the eye to be examined. Figure 3 As shown, the non-contact tonometer 200 may further include a high-speed camera shooting system 230 for recording corneal deformation images, and a fixation optical system 240 for enabling the eye to be examined to perform reference positioning by itself.

[0034] like Figure 2 As shown, in some non-limiting embodiments, the blowing device 210 may be composed of an air pumping device 211, an air cavity 212, a nozzle 213, a chamber plane mirror 226, and a chamber plane mirror 227. The air pumping device 211 blows the compressed air toward the measurement position E through the air cavity 212 and the nozzle 213 to achieve blowing toward the cornea of ​​the eye to be inspected. Figure 3 As shown, the nozzle 213 may be fixed off-axis at a certain angle to prevent the nozzle 213 from blocking the slit light generated by the slit light source system 220 and projected toward the eye to be inspected.

[0035] Please continue to refer to Figure 2 and Figure 3 The slit light source system 220 may include a light source 221, a condenser 222, an aperture 223, a lens group 224, a reflector 225, and a chamber plane mirror 226 and a chamber plane mirror 227 which are used to form the air blowing device 210. The light emitted by the light source 221 is focused on the aperture 223 by the condenser 222, and then formed on the cornea of ​​the eye to be inspected along the axis through the lens group 224, forming an optical section on the cornea, which can clearly show the section shape of the cornea.

[0036] like Figure 3 As shown, the high-speed camera shooting system 230 may include a lens group 231 and a high-speed camera sensor 232. In order to eliminate the interference of the depth of field of the lens so that each position of the cornea of ​​the subject's eye during the deformation process can be clearly photographed, the lens group 231 is located on the main plane, the cornea of ​​the subject's eye is located on the tangent plane, and the receiving surface of the high-speed camera sensor 232 can be placed based on Sham's law. As a result, the high-speed camera shooting system 230 can clearly record the deformation image of the corneal tangent plane during the entire blowing process.

[0037] The fixation optical system 240 may be composed of a light source 241, an aperture 242, and a lens 243. The light emitted by the light source 241 passes through the aperture 242 and the lens 243, and then is introduced into the eye to be examined along the axis through the reflector 201 and the reflector 225 of the non-contact tonometer 200. When the subject is testing the intraocular pressure, the subject can fix the line of sight by looking at the light emitted by the light source 241 and introduced into the eye to be examined, thereby suppressing the movement of the eye.

[0038] The positioning system of the non-contact tonometer 200 may include an XY direction positioning module for positioning the eye under examination in XY direction and a Z direction positioning module for positioning the eye under examination in Z direction. The XY direction positioning module and the Z direction positioning module may include a projection unit and a light receiving unit, respectively.

[0039] In some non-limiting embodiments, Figure 2 As shown, the projection unit 250 of the XY direction positioning module may include multiple groups of light sources 251, aperture holes 252 and lenses 253. The multiple groups of light sources 251, aperture holes 252 and lenses 253 may be fixed symmetrically along the axis in a circular surrounding form to form a projection spot on the cornea of ​​the eye to be inspected.

[0040] Please refer to Figure 4 , Figure 4 A schematic diagram showing the position of a projection unit 250 of an XY direction positioning module of a non-contact tonometer 200 provided according to some embodiments of the present invention is shown.

[0041] like Figure 4 As shown, the projection unit 250 of the XY direction positioning module may include 6 groups of light sources 251, aperture holes 252 and lenses 253. The 6 groups of light sources 251, aperture holes 252 and lenses 253 may be fixed symmetrically along the axis in a circular surround form to project the light emitted by the light source 251 onto the cornea of ​​the eye to be inspected, forming 6 projection spots on the cornea of ​​the eye to be inspected.

[0042] like Figure 3As shown, the light receiving unit 260 of the XY direction positioning module may include a lens group 261 and an image sensor 262. The light receiving unit 260 of the XY direction positioning module may photograph the eye to be inspected to obtain an image of the human eye. When the eye to be inspected moves in the XY direction, the relative positions of the six projection light spots generated by the projection unit 250 of the XY direction positioning module and the pupil of the eye to be inspected will change. Whether the positioning of the eye to be inspected in the XY direction is accurate can be determined based on the relative positions of the projection light spots and the pupil.

[0043] In some embodiments, the projection unit of the Z-direction positioning module of the non-contact tonometer can be shared with the slit light source system, and the light receiving unit can be shared with the high-speed camera shooting system.

[0044] For example, Figure 3 As shown, the projection unit of the Z-direction positioning module can be shared with the slit light source system 220, and the light receiving unit of the Z-direction positioning module can be shared with the high-speed camera shooting system 230. In this way, the Z-direction positioning module can use the high-speed camera shooting system 230 to shoot the human eye image of the eye to be inspected. When the eye to be inspected moves in the Z direction, the position of the optical section generated on the cornea by the slit light source system 220 on the imaging screen of the human eye image will change, and it can be judged whether the positioning of the eye to be inspected in the Z direction is accurate according to the position of the optical section on the human eye image.

[0045] The following will first describe the working principle of the measurement system and non-contact tonometer of the above-mentioned non-contact tonometer in combination with some embodiments of the measurement method of the non-contact tonometer. Those skilled in the art can understand that the embodiments of the measurement method of these non-contact tonometers are only some non-limiting implementation methods provided by the present invention, which are intended to clearly demonstrate the main concept of the present invention and provide some specific solutions that are convenient for the public to implement, rather than to limit the measurement system and all functions or all working modes of the non-contact tonometer. Similarly, the measurement system and non-contact tonometer of the non-contact tonometer are also only a non-limiting implementation method provided by the present invention, and do not constitute a limitation on the execution subject and execution order of each step in the measurement method of these non-contact tonometers.

[0046] The accuracy of intraocular pressure measurement of the non-contact tonometer is affected by the position of the eye to be examined. Therefore, the examinee needs to place the eye to be examined at the measurement position E, and the non-contact tonometer accurately positions the eye to be examined. The examinee can place the eye to be examined on the eye fixator and fix it, and look at the light spot generated by the fixation optical system. When the eye to be examined is fixed, the measurement system of the non-contact tonometer can achieve accurate positioning and adjustment of the eye to be examined through the XY direction positioning module and the Z direction positioning module of the positioning system of the non-contact tonometer.

[0047] Please refer to Figure 5 , Figure 5 A flow chart of a measurement method of a non-contact tonometer provided according to some embodiments of the present invention is shown.

[0048] like Figure 5 As shown, the non-contact tonometer measurement method 500 may include step S510: acquiring a first human eye image in the XY direction and a second human eye image in the Z direction of the eye to be inspected.

[0049] by Figures 2 to 4 Taking the non-contact tonometer 200 shown in the figure as an example, the non-contact tonometer 200 can take a first human eye image of the subject's eye in the XY direction through the light receiving unit 260 of the XY direction positioning module. The second human eye image of the subject's eye in the Z direction is taken through the light receiving unit of the Z direction positioning module. Figure 3 As shown, the non-contact tonometer 200 can capture a second human eye image of the subject's eye in the Z direction through a high-speed camera capturing system 230 shared with a light receiving unit of a Z-direction positioning module.

[0050] Afterwards, the non-contact tonometer may execute step S520: identifying the first human eye image according to the pupil recognition method and the positioning light point detection method to determine the pupil of the eye to be inspected and the centroid of the pupil contour.

[0051] Specifically, the pupil recognition method may first perform edge detection on the first eye image to determine pupil contour candidates.

[0052] The measurement system of the non-contact tonometer can perform edge detection on the first human eye image to determine the possibility that the curve edge segment is an important part of the pupil contour. The curve edge segments with a high possibility of being an important part of the pupil contour are conditionally combined to construct pupil contour candidates that may represent the reconstructed pupil contour.

[0053] In some preferred embodiments, after constructing pupil contour candidates, the measurement system of the non-contact tonometer can eliminate error terms in the pupil contour candidates.

[0054] The measurement system of the non-contact tonometer can first determine the approximate dominant points of the pupil contour candidate by the k-cosine chain approximation method. Each curve edge segment is approximated by the measurement system of the non-contact tonometer as a set of approximate dominant points D. Through the k-cosine chain approximation method, the measurement system of the non-contact tonometer can reduce the amount of calculation. In addition, when the pupil area is not correctly separated from the surrounding edges, a better ellipse fitting result can be obtained when the pupil contour candidate is subsequently fitted.

[0055] Afterwards, after completing the approximation, the measurement system of the non-contact tonometer can calculate the approximate dominant point of the pupil contour candidate through a heuristic rule to eliminate the error term in the pupil contour candidate.

[0056] In some embodiments, the measurement system of the non-contact tonometer may apply several heuristic rules to exclude pupil contour candidates that are unlikely to belong to the pupil contour.

[0057] For example, consider the equation of a cone: ax² + by² + cxy + dx + ey + f = 0, The measurement system of the non-contact tonometer requires at least five points to fit an ellipse by the least square method. Therefore, the measurement system of the non-contact tonometer can discard pupil contour candidates with less than five points approximating the dominant point D as error terms. Thus, the measurement system of the non-contact tonometer can exclude edge segments with simple shapes, such as small segments or straight segments.

[0058] Furthermore, the measurement system of the non-contact tonometer can infer the approximate range of the maximum pupil diameter pdmax and the minimum pupil diameter pdmin. Referring to human physiology, the outer canthal distance of the eye can be approximated to 27.6 mm, the value of the maximum pupil diameter pdmax can be 8 mm, and the value of the minimum pupil diameter pdmin can be 2 mm. The maximum pupil diameter pdmax is independent of the position of the camera sensor of the light receiving unit, but the value of the minimum pupil diameter pdmin may fail due to perspective projection distortion and corneal refraction. Nevertheless, the minimum pupil diameter pdmin represents a tiny portion (about 4.8%) of the image diagonal, so the measurement system of the non-contact tonometer still retains this lower limit. For each pupil contour candidate segment, the measurement system of the non-contact tonometer can approximate the diameter of the pupil contour candidate segment by the maximum spacing between points within the segment. If the diameter of the pupil contour candidate segment exceeds the range [pdmin, pdmax], the pupil contour candidate segment is excluded.

[0059] For another example, in order to estimate the curvature of the candidate segment of the pupil contour, the measurement system of the non-contact tonometer can use the rotating caliper method to calculate the minimum enclosing rectangle containing the approximate dominant point D. The curvature is estimated based on the ratio of the minimum and maximum side lengths of the minimum enclosing rectangle. The straighter the candidate segment of the pupil contour, the smaller the ratio of the minimum and maximum side lengths of the minimum enclosing rectangle. The measurement system of the non-contact tonometer can set a cutoff threshold based on the ratio of the minor axis to the major axis of the ellipse. In one embodiment, the ratio of the minor axis to the major axis of the ellipse is Rth≈0.2. Therefore, the measurement system of the non-contact tonometer can use this heuristic rule to exclude relatively straight candidate segments of the pupil contour.

[0060] In some embodiments, for each pupil contour candidate, the measurement system of the non-contact tonometer can fit an ellipse based on the pupil contour candidate. The pupil confidence metric of the pupil contour candidate is then evaluated based on the ellipticity, the angular edge distribution, and the ellipse contour contrast. The pupil confidence metric can be used to characterize the confidence that the ellipse is the pupil. The measurement system of the non-contact tonometer can select the pupil contour candidate with the highest pupil confidence metric as the pupil of the eye to be examined.

[0061] In a preferred embodiment, the measurement system of the non-contact tonometer can calculate the pupil confidence for the remaining pupil contour candidates after eliminating the error term.

[0062] In some embodiments, for each pupil contour candidate, the measurement system of the non-contact tonometer can use three metrics: ellipticity, angular edge distribution, and ellipse contour contrast to evaluate the pupil confidence that the pupil contour candidate is the pupil. The above three metrics can be determined based on the aspect ratio of the ellipse, the angular distribution of the edge relative to the ellipse, and the proportion of ellipse contour points that support the assumption that the ellipse is the pupil.

[0063] The metric of ellipticity favors ellipses that are closer to a circle and is determined by evaluating the ratio of the minor axis to the major axis of the ellipse. The angular marginal distribution θ can be used to evaluate the angular distribution of the points in the approximate dominant point D relative to the ellipse and can be approximated as the proportion of the points in the approximate dominant point D that occupy the central quadrant of the ellipse. If the angular marginal distribution θ is reasonable, the pupil outline candidate is more likely to be derived from an elliptical shape (i.e., the pupil). The ellipse outline contrast γ can be used to determine whether the pupil outline candidate supports the hypothesis of the pupil appearance by examining the outline points of the ellipse. The darker area of ​​the pupil is surrounded by the brighter area, and the measurement system of the non-contact tonometer can be approximated by selecting the outline points of the ellipse every 10 degrees. If the average brightness of the inner segment of the line segment passing through the outline point is lower than that of the outer segment, then the outline point supports the hypothesis of the pupil appearance. The ellipse outline contrast γ can be determined by the proportion of the ellipse outline points that support the hypothesis that the ellipse is the pupil.

[0064] Through the pupil recognition method, the non-contact tonometer can also ensure that the subject's eye is placed in the measurement position and is in an open state before determining the centroid of the pupil contour.

[0065] In addition, the positioning light spot detection method can be based on the pupil, and can perform binarization, contour detection, ellipse fitting and centroid search on the first human eye image to determine the centroid of the pupil contour.

[0066] Specifically, the measurement system of the non-contact tonometer can process the image and find the target point through contour fitting and specific heuristic rules. Then, the measurement system of the non-contact tonometer can perform binarization, contour detection, ellipse fitting, and find the centroid closest to the target point.

[0067] Specifically, the measurement system of the non-contact tonometer can first read the input image and convert the image into a grayscale image, and then set the target point. The expected target point is the reference point that the measurement system of the non-contact tonometer seeks, such as (246, 182).

[0068] Afterwards, the measurement system of the non-contact tonometer can convert the grayscale image into a binary image. The area where the pixel value exceeds the threshold is set to 255 (white), otherwise it is 0 (black). In some embodiments, the threshold can be set to 200.

[0069] In order to improve the processing speed, the measurement system of the non-contact tonometer can only process an area around the target point, namely the region of interest (ROI). Through calculation, the starting coordinates of the ROI area are determined to be (dx, dy), and the boundary check of the ROI area is performed to ensure that the ROI area does not exceed the image boundary. The measurement system of the non-contact tonometer searches for contours in the ROI area and saves the detected contours.

[0070] The measurement system of the non-contact tonometer can filter and fit contours that meet the conditions. For example, the measurement system of the non-contact tonometer can filter the contours by area filtering and aspect ratio filtering. Area filtering can first calculate the area of ​​each contour. If the area is less than the set area lower limit minArea or greater than the area upper limit maxArea, the contour is skipped, that is, the contour is screened out. Aspect ratio filtering can calculate the aspect ratio (ratio of the major axis to the minor axis) of the fitted ellipse. In some embodiments, if the aspect ratio of the fitted ellipse is greater than 2, the contour is considered to be too flat and the contour is skipped.

[0071] Afterwards, the measurement system of the non-contact tonometer can calculate the centroid of the screened contours. Then the distance between the centroid of each contour and the target point is calculated, and the contour with the minimum distance is retained. Here, the positioning light spot detection method can generate multiple results, and the multiple results generated can be combined with the results of the pupil determined by the pupil recognition method for screening, so as to determine the centroid of the pupil of the eye under examination and the pupil contour.

[0072] Please continue to refer to Figure 5 The non-contact tonometer measurement method 500 may further include step S530: identifying the corneal bright line of the second human eye image according to the corneal bright line detection method to determine the corneal vertex of the eye to be inspected.

[0073] The measurement system of the non-contact tonometer can perform contour detection and contour merging on the second human eye image through the corneal bright line detection method to determine the corneal bright line. Specifically, the corneal bright line detection method can perform contour detection, then accelerate the search for neighboring points between contours by constructing a spatial index, and process the contour data through an optimized merging algorithm, and finally extract the longest curve contour for related calculations.

[0074] In some embodiments, the measurement system of the non-contact tonometer may first perform edge detection on the second human eye image based on the Canny algorithm to determine the edge contour.

[0075] Here, the measurement system of the non-contact tonometer can pre-process the image before edge detection. The pre-processing can include converting the image into a grayscale image, converting the image into a binary image using threshold processing, and then cleaning the noise in the image using morphological operations.

[0076] Please refer to Figure 6 , Figure 6 A schematic diagram of a second human eye image provided according to some embodiments of the present invention is shown.

[0077] Figure 6 The second eye image shown is a grayscale image, which shows a bright curve on a dark background with some noise points. The measurement system of the non-contact tonometer can represent the pixel intensity I(x,y) at each coordinate (x,y) in the image with a value in the range of (0~255).

[0078] The measurement system of the non-contact tonometer can create a binary image B(x,y) based on the set pixel intensity threshold T: B(x,y) = { 1, if I(x,y)≥T 0, otherwise}, When the pixel intensity I(x,y) is greater than the threshold T, the coordinate can be considered to be the position of the bright curve, otherwise, the coordinate can be considered to be in the background. Thus, the binary image B(x,y) created by the measurement system of the non-contact tonometer changes the bright curve to white (1) and the background to black (0).

[0079] Afterwards, the measurement system of the non-contact tonometer can use morphological operations (e.g., opening operations) to remove small bright spots from the background.

[0080] The processed image is edge detected by the Canny algorithm to generate a clear edge outline. The Canny algorithm can include Gaussian smoothing, gradient calculation, non-maximum suppression and hysteresis threshold.

[0081] The measurement system of the non-contact tonometer can then perform edge contour detection to identify the main curves. Figure 6 In the second human eye image shown, the measurement system of the non-contact tonometer can obtain a main long contour, namely, an arc curve in the figure, through edge contour detection.

[0082] Next, the measurement system of the non-contact tonometer can search for neighboring points of the contour points of the edge contour through the spatial index accelerator, and merge the contour points and the neighboring points to obtain the neighboring contour.

[0083] The measurement system of the non-contact tonometer uses a grid-based spatial index accelerator to accelerate the merging of contours and the search for neighboring points. Figure 6 In the embodiment shown, the measurement system of the non-contact tonometer can divide the image space into grid units of size 5, and all contour points are inserted into the corresponding grids according to the coordinate positions. Each grid unit stores the contour points in the area and the contour index to which the contour points belong. The measurement system of the non-contact tonometer can search for the neighboring points of a contour point from the spatial index accelerator. The neighboring points of the contour point can be determined by accessing the grid where the contour point is located and the surrounding grids within the distance threshold. For example, Figure 6 For example, the neighboring points of a contour point can be determined by accessing the grid where the contour point is located and the 8 grids around it. Afterwards, the neighboring contour can be obtained by merging the contour point and the neighboring points.

[0084] Afterwards, the measurement system of the non-contact tonometer can process the neighboring contours by an optimized merging algorithm. For example, the measurement system of the non-contact tonometer can use a depth-first search (DFS) to merge neighboring contours with a short distance. The neighboring contours within a distance threshold are merged into one group to obtain a merged merged contour.

[0085] After obtaining the merged combined contour, the measurement system of the non-contact tonometer determines the combined contour with the largest span as the corneal bright line based on the span of the X axis of the combined contour. Here, the span of the X axis can be determined by the difference between the maximum X value and the minimum X value of the combined contour.

[0086] Specifically, the measurement system of the non-contact tonometer can use a polynomial approximation method to simplify the merged contour after selecting the merged contour with the largest span. In some embodiments, a polygonal approximation algorithm is used to subsample the merged contour to reduce the number of contour points and obtain a simplified contour. Then, a spline curve fitting algorithm is used for the simplified contour to generate a smooth curve.

[0087] Based on the identified corneal bright line, the measurement system of the non-contact tonometer can determine the corneal apex of the eye being examined.

[0088] Please continue to refer to Figure 5 The non-contact tonometer measurement method 500 may include step S540: performing XY direction positioning adjustment based on the centroid of the pupil and the pupil contour, and performing Z direction positioning adjustment based on the corneal vertex and the calibration point in the Z direction.

[0089] The non-contact tonometer can adjust the optical axis to achieve rough positioning in the XY direction based on the centroid of the pupil and pupil contour. After that, the XY direction positioning is adjusted until the projected light spot is concentric with the pupil. In addition, the Z direction positioning is adjusted until the calibration point calibrated in the Z direction, that is, the calibrated measurement position corneal vertex, coincides with the corneal vertex, completing the Z direction positioning.

[0090] In this way, by combining the pupil recognition method, the positioning light spot detection method, and the corneal bright line detection method, the non-contact tonometer can calculate and locate the center point of the cornea, thereby ensuring the accuracy of the positioning of the eye being examined.

[0091] Please continue to refer to Figure 5 The non-contact tonometer can execute step S550: in response to the completion of the XY direction positioning adjustment and the Z direction positioning adjustment, blow air into the eye to be inspected to obtain a corneal deformation image during the blowing process captured by a high-speed camera sensor.

[0092] by Figures 2 to 4 Taking the non-contact tonometer 200 shown as an example, once the positioning in the XY direction and the Z direction is confirmed to be consistent, the blowing device 210 can spray air to the cornea of ​​the eye to be inspected through the nozzle 213. The slit light source system 220 is turned on synchronously to project a slit light spot onto the cornea of ​​the eye to be inspected, forming an optical section on the cornea. At the same time, the high-speed camera shooting system 230 records the deformation state of the cornea during the blowing process in real time at a high frame rate. Thus, the measurement system of the non-contact tonometer can obtain the corneal deformation image during the blowing process captured by the high-speed camera sensor.

[0093] Afterwards, the non-contact tonometer measurement method 500 may include step S560: determining the intraocular pressure value of the eye to be examined based on the corneal thickness and corneal curvature determined by the corneal deformation image and the pressure change curve of the air insufflation cavity.

[0094] The thickness of the cornea has a great influence on the measurement result of intraocular pressure. Taking the non-contact tonometer 200 as an example, since the cornea is an elastically deformable membrane, after the blowing device 210 blows air, the cornea will produce a reaction force opposite to the deformation force applied by the blowing device 210. This reaction force has nothing to do with the intraocular pressure itself, but it will affect the measurement result of the intraocular pressure. Taking into account the elastic properties of the cornea, the measurement system of the non-contact tonometer can infer the thickness of the cornea from the deformation image of the cornea, and further estimate the reaction force generated by the cornea during the elastic deformation of the cornea from the corneal thickness, and use the reaction force as an influencing factor for deriving intraocular pressure. In addition, corneal curvature is also a factor that affects intraocular pressure. The measurement system of the non-contact tonometer can derive the corneal curvature from the deformation image of the cornea.

[0095] In this way, the measurement system of the non-contact tonometer can use image processing methods to analyze the corneal deformation image obtained by the high-speed camera sensor to determine the corneal thickness and corneal curvature. Combined with the pressure change curve in the air chamber during blowing, the intraocular pressure value of the eye under test is derived, which greatly improves the measurement accuracy of the intraocular pressure value of the eye under test.

[0096] In summary, the non-contact tonometer measurement method, non-contact tonometer measurement system and non-contact tonometer accurate positioning method in the XY direction and the Z direction provided by the present invention, as well as determining the corneal thickness and corneal curvature by recording the corneal deformation image, and calculating the intraocular pressure value of the eye under test based on the corneal thickness and the corneal curvature, greatly improve the measurement accuracy of the non-contact tonometer.

[0097] Although the above methods are illustrated and described as a series of actions for simplicity of explanation, it should be understood and appreciated that these methods are not limited by the order of the actions, because according to one or more embodiments, some actions may occur in a different order and / or concurrently with other actions from those illustrated and described herein or not illustrated and described herein but understandable to those skilled in the art.

[0098] Those skilled in the art will appreciate that information, signals, and data may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips cited throughout the above description may be represented by voltage, current, electromagnetic waves, magnetic fields or magnetic particles, optical fields or optical particles, or any combination thereof.

[0099] Those skilled in the art will further appreciate that the various illustrative logic blocks, modules, circuits, and algorithm steps described in conjunction with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or a combination of the two. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps are generally described above in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. The technician may implement the described functionality in different ways for each specific application, but such implementation decisions should not be interpreted as resulting in a departure from the scope of the present invention.

[0100] The various illustrative logic modules and circuits described in conjunction with the embodiments disclosed herein may be implemented or executed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in an alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in cooperation with a DSP core, or any other such configuration.

[0101] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software module may reside in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to a processor so that the processor can read and write information from / to the storage medium. In an alternative, a storage medium may be integrated into a processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In an alternative, the processor and the storage medium may reside in a user terminal as discrete components.

[0102] In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented as a computer program product in software, each function may be stored on or transmitted by a computer-readable medium as one or more instructions or codes. Computer-readable media include both computer storage media and communication media, including any media that facilitates the transfer of a computer program from one place to another. Storage media may be any available media that can be accessed by a computer. As an example and not limitation, such a computer-readable medium may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage device, or any other medium that can be used to carry or store the desired program code in the form of an instruction or data structure and can be accessed by a computer. Any connection is also properly referred to as a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwaves, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwaves are included in the definition of the medium. Disk and disc as used herein include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0103] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to those skilled in the art, and the general principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein, but should be granted the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring non-contact tonometer, characterized in that: Includes steps: Acquire a first human eye image in the XY direction and a second human eye image in the Z direction of the eye to be inspected; Recognize the first human eye image according to a pupil recognition method and a positioning light point detection method to determine the pupil of the eye to be inspected and the centroid of the pupil contour; Identify the corneal bright line of the second human eye image according to the corneal bright line detection method to determine the corneal vertex of the eye to be inspected; Performing XY direction positioning adjustment based on the centroid of the pupil and the pupil contour, and performing Z direction positioning adjustment based on the corneal vertex and the calibration point in the Z direction; In response to the XY direction positioning adjustment and the Z direction positioning adjustment being completed, blowing air into the eye to be inspected to obtain a corneal deformation image during the blowing process captured by a high-speed camera sensor; as well as The intraocular pressure value of the eye to be inspected is determined based on the corneal thickness and corneal curvature determined by the corneal deformation image and the pressure change curve of the air insufflation cavity.

2. The method for measuring non-contact tonometer according to claim 1, characterized in that: The step of identifying the first human eye image according to the pupil identification method and the positioning light point detection method to determine the pupil of the eye to be inspected and the centroid of the pupil contour includes: Performing edge detection on the first human eye image to determine pupil contour candidates; Determine the approximate dominant point of the pupil contour candidate by a k-cosine chain approximation method; Calculating the approximate dominant point of the pupil contour candidate by a heuristic rule to eliminate error terms in the pupil contour candidate; calculating pupil confidences of the remaining pupil contour candidates, and determining the pupil of the eye to be inspected based on the pupil confidences; and Based on the pupil, binarization processing, contour detection, ellipse fitting and centroid search are performed on the first human eye image to determine the centroid of the pupil contour.

3. The non-contact tonometer measuring method according to claim 1, characterized in that: The corneal bright line detection method comprises the steps of: Contour detection and contour merging are performed on the second human eye image to determine the corneal bright line.

4. The method for measuring non-contact tonometer according to claim 3, characterized in that: The step of performing contour detection and contour merging on the second human eye image to determine the corneal bright line comprises: Performing edge detection on the second human eye image based on the Canny algorithm to determine an edge contour; Performing neighboring point search on the contour points of the edge contour by using a spatial index accelerator; Merging the contour point and the neighboring point to obtain a neighboring contour; merging the adjacent contours within a distance threshold to obtain a merged contour; and Based on the span of the X-axis, the merged contour with the largest span is determined as the corneal bright line.

5. A non-contact tonometer measurement system, characterized in that: include: a memory having computer instructions stored thereon; as well as A processor is connected to the memory and is configured to execute computer instructions stored in the memory to implement the measurement method of the non-contact tonometer according to any one of claims 1 to 4.

6. A non-contact tonometer, comprising an air blowing device, a slit light source system and a fixation optical system, characterized in that: Also includes: A positioning system, wherein the positioning system comprises an XY direction positioning module and a Z direction positioning module, wherein the XY direction positioning module and the Z direction positioning module respectively comprise a projection unit and a light receiving unit; A high-speed camera shooting system is used to record the corneal deformation image during the corneal deformation process; as well as The measurement system of the non-contact tonometer as claimed in claim 5.

7. The non-contact tonometer according to claim 6, characterized in that: The projection unit of the XY direction positioning module includes a plurality of light sources, apertures and lenses, which are fixed symmetrically along an axis in a circular surrounding form, and are used to form a projection spot on the cornea of ​​the eye to be inspected; and The light receiving unit includes a lens group and an image sensor.

8. The non-contact tonometer according to claim 6, characterized in that: The projection unit of the Z-direction positioning module is shared with the slit light source system, and the light receiving unit is shared with the high-speed camera shooting system.

9. The non-contact tonometer according to claim 6, characterized in that: The high-speed camera shooting system includes a lens group and a high-speed camera sensor, the lens group is located on the main plane, the cornea of ​​the eye to be inspected is located on the tangent plane, and the receiving surface of the high-speed camera sensor is arranged based on Schaam's law.

10. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the computer instructions are executed by the processor, the measurement method of the non-contact tonometer according to any one of claims 1 to 4 is implemented.

Images