Non-contact tonometer measurement method, system and non-contact tonometer

Abstract

The present invention provides a non-contact tonometer measurement method and a non-contact tonometer. The non-contact tonometer measurement method includes the following steps: obtaining a first human eye image in the XY direction and a second human eye image in the Z direction of a subject's eye; identifying the first human eye image according to a pupil recognition method and a positioning light point detection method to determine the centroid of the pupil and pupil contour of the subject's eye; identifying the corneal bright line in the second human eye image according to a corneal bright line detection method to determine the corneal vertex of the subject's eye; performing XY direction positioning adjustment based on the centroid of the pupil and pupil contour, and performing Z direction positioning adjustment based on the corneal vertex and a calibration point in the Z direction; in response to completion of the XY direction positioning adjustment and the Z direction positioning adjustment, blowing air into the subject's eye to obtain a corneal deformation image captured by a high-speed camera sensor; and determining the intraocular pressure value of the subject's eye based on the corneal thickness and corneal curvature determined from the corneal deformation image and the pressure change curve of the blowing air chamber.

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, one of the three leading causes of blindness, is an eye disease characterized by intermittent or persistent elevation of intraocular pressure. Sustained high intraocular pressure damages various eye structures and visual function. Left untreated, it can lead to complete loss of vision and blindness.

[0003] Intraocular pressure testing is an effective way to diagnose glaucoma. In the existing technology, non-contact tonometers project air onto the eye along the direction of the optical axis, causing the cornea to gradually flatten and eventually sink. 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 results of corneal deformation. Therefore, the measurement accuracy of the existing non-contact tonometer is low.

[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 for the non-contact tonometer, which can improve the measurement accuracy of intraocular pressure. Summary of the Invention

[0005] The following is a brief summary of one or more aspects to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceivable aspects and is neither intended to identify key or critical elements of all aspects nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that will be provided later.

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a non-contact tonometer measurement method, a non-contact tonometer measurement system, 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: obtaining 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 a calibration point in the Z direction; in response to 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 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; determining the approximate dominant point of the pupil contour candidate; calculating the approximate dominant point of the pupil contour candidate by heuristic rules to eliminate error terms in the pupil contour candidate; 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 includes 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 that the merged contour with the largest span is the corneal bright line.

[0011] Furthermore, the non-contact tonometer measurement system provided in accordance with 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 configured to execute the computer instructions stored in the memory to implement the non-contact tonometer measurement method provided in any 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 for recording corneal deformation images during corneal deformation; 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 respectively include a projection unit and a light receiving unit.

[0014] Preferably, in one embodiment of the present invention, the projection unit of the XY direction positioning module includes multiple groups of light sources, apertures and lenses, and the multiple groups of light sources, apertures 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 placed based on Scham's law.

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

[0018] The above features and advantages of the present invention will 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 characteristics may have the same or similar reference numerals.

[0019] Figure 1 A schematic diagram of a non-contact tonometer measurement system according to some embodiments of the present invention is shown;

[0020] Figure 2 A planar schematic diagram of an optical system of a non-contact tonometer 200 provided according to some embodiments of the present invention is shown;

[0021] 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;

[0022] Figure 4 A schematic diagram showing the position of the projection unit 250 of the XY direction positioning module of the non-contact tonometer 200 provided according to some embodiments of the present invention is shown;

[0023] Figure 5 A flowchart showing a measurement method of a non-contact tonometer according to some embodiments of the present invention; and

[0024] Figure 6 A schematic diagram of a second human eye image provided according to some embodiments of the present invention is shown.

[0025] Reference numerals:

[0026] 100: Non-contact tonometer measurement system;

[0027] 110: memory;

[0028] 111: Computer readable storage medium;

[0029] 120: Processor;

[0030] 200: Non-contact tonometer;

[0031] 201: reflector;

[0032] 210: blowing device;

[0033] 211: Inflating device;

[0034] 212: air cavity;

[0035] 213: nozzle;

[0036] 220: Slit light source system;

[0037] 221: Light source;

[0038] 222: Condenser;

[0039] 223: aperture;

[0040] 224: lens group;

[0041] 225: reflector;

[0042] 226: chamber plane mirror;

[0043] 227: chamber plane mirror;

[0044] 230: High-speed camera shooting system;

[0045] 231: lens group;

[0046] 232: High-speed camera sensor;

[0047] 240: fixation optical system;

[0048] 241: Light source;

[0049] 242: aperture;

[0050] 243: Lens;

[0051] 250: projection unit of XY direction positioning module;

[0052] 251: Light source;

[0053] 252: aperture;

[0054] 253: Lens;

[0055] 260: Light receiving unit of XY direction positioning module;

[0056] 261: lens group;

[0057] 262: Image sensor;

[0058] 500: Measurement method of non-contact tonometer;

[0059] E: measurement location; and

[0060] S510~S560: steps. DETAILED DESCRIPTION

[0061] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Note that the various aspects described below with reference to the accompanying drawings and specific embodiments are merely exemplary and should not be construed as limiting the scope of protection of the present invention.

[0062] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0063] Furthermore, the terms "upper," "lower," "left," "right," "top," "bottom," "horizontal," and "vertical" used in the following description should be understood to refer to the orientations depicted in that section and the accompanying drawings. These relative terms are used solely for convenience of description and do not necessarily imply that the devices described herein must be manufactured or operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0064] It will be understood that although the terms "first," "second," "third," etc. may be used herein to describe various components, regions, layers, and / or portions, these components, regions, layers, and / or portions should not be limited by these terms, and these terms are merely used to distinguish different components, regions, layers, and / or portions. Thus, a first component, region, layer, and / or portion discussed below may be referred to as a second component, region, layer, and / or portion without departing from some embodiments of the present invention.

[0065] As mentioned above, 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, causing the cornea to gradually flatten and eventually sink. 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 results of the corneal deformation. Therefore, the measurement accuracy of the existing non-contact tonometer is low.

[0066] In order to overcome the above-mentioned defects of the prior art, the present invention provides a non-contact tonometer measurement method, a non-contact tonometer measurement system, a non-contact tonometer, and a computer-readable storage medium, which can improve the measurement accuracy of intraocular pressure.

[0067] 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.

[0068] 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.

[0069] like Figure 1 As shown, the non-contact tonometer measurement system 100 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 non-contact tonometer measurement method provided in the first aspect of the present invention.

[0070] In some embodiments, the non-contact tonometer measurement system may be configured in the non-contact tonometer to implement the non-contact tonometer measurement method provided by the first aspect of the present invention through the non-contact tonometer.

[0071] The non-contact tonometer may include an air blowing device for blowing air into the cornea of ​​the eye to deform it, a slit light source system for projecting slit light onto the eye, a fixation optical system for enabling the eye to self-position itself, a positioning system, a high-speed camera system, and a non-contact tonometer measurement system. The positioning system may include an XY positioning module for XY positioning of the eye and a Z positioning module for Z positioning of the eye. The high-speed camera system may be used to record images of the corneal cross-section during corneal deformation.

[0072] Please refer to Figure 2 and Figure 3 , Figure 2 FIG2 shows a planar schematic diagram of an optical system of a non-contact tonometer 200 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.

[0073] like Figure 2 As shown, the subject needs to place the eye to be examined at the measurement position E. 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 inspected to perform reference positioning by itself.

[0074] like Figure 2As 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 can 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.

[0075] 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 assembly 224, a reflector 225, and chamber plane mirrors 226 and 227, which also constitute the air blowing device 210. Light emitted by the light source 221 is focused on the aperture 223 by the condenser 222, and then passes through the lens assembly 224 along the axis to form an image on the cornea of ​​the eye being examined, forming an optical section on the cornea, which can clearly show the cross-sectional shape of the cornea.

[0076] like Figure 3 As shown, the high-speed camera system 230 may include a lens assembly 231 and a high-speed camera sensor 232. To eliminate interference from the lens' depth of field and ensure clear images of the cornea at every position during its deformation, the lens assembly 231 is positioned on the principal plane, the cornea on the tangent plane, and the receiving surface of the high-speed camera sensor 232 is positioned according to Scham's law. This allows the high-speed camera system 230 to clearly record the deformation of the corneal tangent plane throughout the entire air-puffing process.

[0077] The fixation optical system 240 can be composed of a light source 241, an aperture 242, and a lens 243. Light emitted from the light source 241 passes through the aperture 242 and lens 243, and then is guided along the axis of the non-contact tonometer 200 by the reflector 201 and the reflector 225 into the subject's eye. During the intraocular pressure measurement, the subject can fix their line of sight by focusing on the light emitted by the light source 241 and guided into the subject's eye, thereby suppressing eye movement.

[0078] The positioning system of the non-contact tonometer 200 may include an XY positioning module for positioning the eye under examination in XY direction and a Z positioning module for positioning the eye under examination in Z direction. The XY positioning module and the Z positioning module may include a projection unit and a light receiving unit, respectively.

[0079] In some non-limiting embodiments, Figure 2As 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.

[0080] Please refer to Figure 4 , Figure 4 A schematic diagram illustrating the position of the projection unit 250 of the XY direction positioning module of the non-contact tonometer 200 provided according to some embodiments of the present invention is shown.

[0081] 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 surrounding 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.

[0082] like Figure 3 As 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 can capture the subject's eye to obtain an image of the human eye. When the subject's eye moves in the XY direction, the relative positions of the six projected light spots generated by the projection unit 250 of the XY direction positioning module and the pupil of the subject's eye will change. The relative positions of the projected light spots and the pupil can be used to determine whether the subject's eye is accurately positioned in the XY direction.

[0083] 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.

[0084] 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 imaging system 230. In this way, the Z-direction positioning module can use the high-speed camera imaging system 230 to capture an image of the subject's eye. As the subject's eye moves in the Z direction, the position of the optical section created on the cornea by the slit light source system 220 changes within the image of the subject's eye. The position of this optical section within the image of the subject's eye can be used to determine whether the subject's Z-direction positioning is accurate.

[0085] The following will first describe the working principle of the above-mentioned non-contact tonometer measurement system and non-contact tonometer in conjunction with some embodiments of the measurement method of the non-contact tonometer. Those skilled in the art will 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 all functions or all working modes of the measurement system and non-contact tonometer 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.

[0086] The accuracy of IOP measurements using a non-contact tonometer is affected by the position of the eye being examined. Therefore, the subject must place the eye at measurement position E, and the non-contact tonometer accurately positions the eye. The subject can place the eye on an eye holder and fixate it while gazing at the light spot generated by the fixation optical system. While the eye is fixed, the non-contact tonometer's measurement system accurately positions the eye using the XY and Z positioning modules of the non-contact tonometer's positioning system.

[0087] 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.

[0088] 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 subject's eye.

[0089] by Figures 2 to 4 Taking the non-contact tonometer 200 shown in the figure as an example, the non-contact tonometer 200 can capture the 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 captured by 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 the light receiving unit of the Z-direction positioning module.

[0090] 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.

[0091] Specifically, the pupil recognition method may first perform edge detection on the first eye image to determine pupil contour candidates.

[0092] The measurement system of the non-contact tonometer can perform edge detection on the first eye image to determine the likelihood that a curved edge segment is a significant portion of the pupil contour. Curved edge segments with a high likelihood of being significant portions of the pupil contour are conditionally combined to construct pupil contour candidates that may represent the reconstructed pupil contour.

[0093] In some preferred embodiments, after constructing pupil contour candidate items, the measurement system of the non-contact tonometer can eliminate error items in the pupil contour candidate items.

[0094] The measurement system of the non-contact tonometer can first determine the approximate dominant points of the pupil contour candidate. Each curve edge segment is approximated by the measurement system of the non-contact tonometer as a set of approximate dominant points D.

[0095] Afterwards, the measurement system of the non-contact tonometer can calculate the approximate dominant point of the pupil contour candidate through a heuristic rule after completing the approximation to eliminate the error term in the pupil contour candidate.

[0096] 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.

[0097] For example, consider the equation of a cone:

[0098] ax² + by² + cxy + dx + ey + f = 0,

[0099] The non-contact tonometer measurement system requires at least five points to fit an ellipse using the least squares method. Therefore, the non-contact tonometer measurement system can discard pupil outline candidates that approximate the dominant point D with fewer than five points as error terms. This allows the non-contact tonometer measurement system to exclude simple edge segments, such as small or straight segments.

[0100] Furthermore, the non-contact tonometer's measurement system can infer approximate ranges for the maximum pupil diameter pdmax and the minimum pupil diameter pdmin. Based on human physiology, the outer canthal distance can be approximated to 27.6 mm, the maximum pupil diameter pdmax can be 8 mm, and the minimum pupil diameter pdmin can be 2 mm. The maximum pupil diameter pdmax is independent of the position of the camera sensor in the light-receiving unit, but the minimum pupil diameter pdmin can be affected by perspective projection distortion and corneal refraction. However, the minimum pupil diameter pdmin represents a tiny fraction (approximately 4.8%) of the image diagonal, so the non-contact tonometer's measurement system maintains this lower limit. For each pupil contour candidate segment, the non-contact tonometer's measurement system approximates the diameter of the candidate segment using the maximum spacing between points within the segment. If the diameter of a pupil contour candidate segment exceeds the range [pdmin, pdmax], the candidate segment is excluded.

[0101] For another example, to estimate the curvature of a candidate pupil contour segment, the measurement system of a non-contact tonometer can use a 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 pupil contour segment, 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 is based on Rth≈0.2. Thus, the measurement system of the non-contact tonometer can use this heuristic rule to exclude relatively straight candidate pupil contour segments.

[0102] 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. A pupil confidence metric of the pupil contour candidate is then evaluated based on the ellipticity, angular edge distribution, and 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 being examined.

[0103] 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.

[0104] In some embodiments, for each pupil outline candidate, the measurement system of the non-contact tonometer can use three metrics: ellipticity, angular edge distribution, and ellipse outline contrast to assess the pupil confidence that the pupil outline candidate is the pupil. The three metrics can be determined based on the aspect ratio of the ellipse, the angular distribution of the edges relative to the ellipse, and the proportion of ellipse outline points that support the hypothesis that the ellipse is the pupil.

[0105] The metric of ellipticity favors ellipses that are closer to a circle and is determined by evaluating the ratio of the ellipse's minor axis to its major axis. The angular marginal distribution θ can be used to evaluate the angular distribution of points in the approximate dominant point D relative to the ellipse and can be approximated as the proportion of points in the approximate dominant point D occupying 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 pupil appearance hypothesis by examining the ellipse's outline points. The pupil is composed of darker regions surrounded by brighter regions. The measurement system of non-contact tonometers can approximate this by selecting ellipse outline points every 10 degrees. If the average brightness of the inner segment of a line segment passing through the outline point is lower than that of the outer segment, the outline point supports the pupil appearance hypothesis. The ellipse outline contrast γ is determined by the proportion of ellipse outline points that support the hypothesis that the ellipse is the pupil.

[0106] 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.

[0107] In addition, the positioning light point detection method can be based on the pupil, and perform binarization processing, contour detection, ellipse fitting and centroid search on the first human eye image to determine the centroid of the pupil contour.

[0108] Specifically, the non-contact tonometer's measurement system can process the image and find the target point through contour fitting and specific heuristic rules. The non-contact tonometer's measurement system can then perform binarization, contour detection, ellipse fitting, and find the centroid closest to the target point.

[0109] 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 a target point. The expected target point is a reference point that the measurement system of the non-contact tonometer seeks, such as (246, 182).

[0110] The measurement system of the non-contact tonometer can then convert the grayscale image into a binary image. Regions where the pixel value exceeds a threshold are set to 255 (white), and otherwise to 0 (black). In some embodiments, the threshold can be set to 200.

[0111] To improve processing speed, the non-contact tonometer's measurement system can process only a region surrounding the target point, known as the Region of Interest (ROI). The starting coordinates of this ROI are calculated to be (dx, dy) and a boundary check is performed to ensure that the ROI does not extend beyond the image boundaries. The non-contact tonometer's measurement system searches for contours within the ROI and saves the detected contours.

[0112] 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 contours through 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 filtered 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 too flat and is skipped.

[0113] The non-contact tonometer's measurement system then calculates the centroid of the filtered contours. It then calculates the distance between each contour's centroid and the target point, retaining the contour with the smallest distance. The localized light point detection method can generate multiple results, which can be combined with the pupil identification method's pupil identification results to determine the centroid of the pupil and the pupil contour of the eye being examined.

[0114] 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.

[0115] The non-contact tonometer's measurement system can perform contour detection and contour merging on the second eye image using a corneal bright line detection method to determine the corneal bright line. Specifically, the corneal bright line detection method performs contour detection, then constructs a spatial index to accelerate the search for neighboring points between contours. It then processes the contour data using an optimized merging algorithm, ultimately extracting the longest curved contour for correlation calculations.

[0116] In some embodiments, the measurement system of the non-contact tonometer may first perform edge detection on the second human eye image based on a Canny algorithm to determine an edge contour.

[0117] Here, the measurement system of the non-contact tonometer can pre-process the image before edge detection. The pre-processing may include converting the image into a grayscale image, converting the image into a binary image using threshold processing, and then using morphological operations to clean up noise in the image.

[0118] 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.

[0119] Figure 6 The second eye image shown is a grayscale image, showing a bright curve on a dark background with some noise. The non-contact tonometer's measurement system can represent the pixel intensity I(x,y) at each coordinate (x,y) in the image using a value in the range of (0-255).

[0120] The measurement system of the non-contact tonometer can create a binary image B(x,y) based on the set pixel intensity threshold T:

[0121] B(x,y) = { 1, if I(x,y)≥T 0, otherwise},

[0122] When the pixel intensity I(x,y) is greater than the threshold T, the coordinate is considered to be the location of the bright curve. Otherwise, the coordinate is 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).

[0123] The measurement system of the non-contact tonometer can then use morphological operations (e.g., opening operation) to remove small bright spots from the background.

[0124] The processed image is then edge detected using the Canny algorithm to generate clear edge contours. The Canny algorithm can include Gaussian smoothing, gradient calculation, non-maximum suppression, and hysteresis thresholding.

[0125] The measuring 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 the arc curve in the figure, through edge contour detection.

[0126] Next, the measurement system of the non-contact tonometer can perform neighboring point search on the contour point of the edge contour through the spatial index accelerator, and merge the contour point and the neighboring points based on the contour point and the neighboring points of the contour point to obtain the neighboring contour.

[0127] The measurement system of the non-contact tonometer uses a grid-based spatial index accelerator to achieve accelerated contour merging and neighbor point search. 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 a contour point can be determined by accessing the grid where the contour point is located and the surrounding grids within a 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. Then, the neighboring contour can be obtained by merging the contour point and the neighboring points.

[0128] The non-contact tonometer measurement system can then process adjacent contours using an optimized merging algorithm. For example, the non-contact tonometer measurement system can use a depth-first search (DFS) to merge adjacent contours that are close to each other. Adjacent contours within a distance threshold are merged into a group to obtain a merged contour.

[0129] After obtaining the merged profile, the measurement system of the non-contact tonometer determines the merged profile with the largest span as the corneal bright line based on the span of the merged profile along the X axis. The span of the X axis can be determined by the difference between the maximum X value and the minimum X value of the merged profile.

[0130] Specifically, after selecting the merged contour with the largest span, the measurement system of the non-contact tonometer can simplify it using a polynomial approximation method. 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. A spline curve fitting algorithm is then applied to the simplified contour to generate a smooth curve.

[0131] 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.

[0132] 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 Z direction calibration point.

[0133] A non-contact tonometer can achieve coarse XY positioning by adjusting the optical axis based on the centroid of the pupil and pupil outline. XY positioning is then adjusted until the projected light spot is concentric with the pupil. Furthermore, Z positioning is adjusted until the Z-calibrated point (i.e., the calibrated measurement location, the corneal vertex) coincides with the corneal vertex, completing Z positioning.

[0134] In this way, by combining the pupil recognition method, the positioning light point 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 positioning the eye being examined.

[0135] 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.

[0136] by Figures 2 to 4 Taking the non-contact tonometer 200 shown as an example, once the XY and Z directions are aligned, the air blowing device 210 sprays air onto the cornea of ​​the eye being examined via the nozzle 213. The slit light source system 220 is simultaneously activated, projecting a slit light spot onto the cornea of ​​the eye being examined, forming an optical section on the cornea. Simultaneously, the high-speed camera system 230 records the deformation of the cornea during the air blowing process in real time at a high frame rate. Thus, the non-contact tonometer's measurement system can capture images of corneal deformation during the air blowing process, captured by the high-speed camera sensor.

[0137] Thereafter, the non-contact tonometer measurement method 500 may include step S560: 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 air insufflation cavity.

[0138] The thickness of the cornea has a great influence on the measurement results 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 results 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 this 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.

[0139] In this way, the non-contact tonometer's measurement system uses image processing to analyze corneal deformation images captured by a high-speed camera sensor to determine corneal thickness and curvature. Combined with the pressure curve within the air chamber during air blowing, this information is used to derive the intraocular pressure (IOP) of the eye being examined, significantly improving IOP measurement accuracy.

[0140] In summary, the non-contact tonometer measurement method, non-contact tonometer measurement system, and non-contact tonometer accurate positioning method in the XY and Z directions provided by the present invention, as well as the determination of corneal thickness and corneal curvature by recording corneal deformation images, and the calculation of the intraocular pressure value of the eye under examination based on the corneal thickness and corneal curvature, greatly improve the measurement accuracy of the non-contact tonometer.

[0141] Although the above methods are illustrated and described as a series of acts for simplicity of explanation, it is to be understood and appreciated that these methods are not limited by the order of the acts, as some acts may occur in a different order and / or concurrently with other acts from those illustrated and described herein or not illustrated and described herein but understandable to those skilled in the art according to one or more embodiments.

[0142] 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 referenced throughout the foregoing description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0143] Those skilled in the art will further appreciate that the various illustrative logic blocks, modules, circuits, and algorithmic steps described in conjunction with the embodiments disclosed herein can 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. A skilled person 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.

[0144] The various illustrative logic modules and circuits described in conjunction with the embodiments disclosed herein may be implemented or executed using 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 the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A 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 conjunction with a DSP core, or any other such configuration.

[0145] The steps of the methods or algorithms 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 RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, 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 the processor so that the processor can read and write information from / to the storage medium. In an alternative, the storage medium may be integrated into the processor. The processor and storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In an alternative, the processor and storage medium may reside in a user terminal as discrete components.

[0146] In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software as a computer program product, the functions may be stored on or transmitted via a computer-readable medium as one or more instructions or code. Computer-readable media includes both computer storage media and communication media, including any medium that facilitates the transfer of a computer program from one location to another. A storage medium may be any available medium that can be accessed by a computer. By way of example and not limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Any connection is also properly referred to as a computer-readable medium. For example, if 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 microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks typically 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.

[0147] 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 is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring non-contact tonometer, characterized in that: Including 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; Identifying the first human eye image according to a pupil identification 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, including: Performing edge detection on the first human eye image to determine pupil contour candidates; calculating a pupil confidence level of the pupil contour candidate and determining the pupil of the eye to be inspected based on the pupil confidence level; 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; 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, the corneal bright line detection method comprising: performing contour detection and contour merging on the second human eye image to determine the corneal bright line; 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 Z direction calibration point; In response to the completion of the XY direction positioning adjustment and the Z direction positioning adjustment, blowing air toward the eye to be inspected to obtain an image of corneal deformation during the blowing process captured by a high-speed camera sensor; and The intraocular pressure value of the eye to be inspected is determined based on the corneal thickness and corneal curvature determined from the corneal deformation image and the pressure change curve of the air insufflation cavity, wherein the corneal thickness is used to estimate the reaction force generated by the cornea during the elastic deformation of the cornea.

2. The method for measuring non-contact tonometer according to claim 1, wherein: Before calculating the pupil confidence of the pupil contour candidate, the method includes the following steps: determining an approximate dominant point of the pupil contour candidate; as well as The approximate dominant points of the pupil contour candidates are calculated by heuristic rules to eliminate error terms in the pupil contour candidates.

3. The measuring method of the non-contact tonometer according to claim 1, wherein: 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 a 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 adjacent point to obtain an adjacent 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 to be the corneal bright line.

4. 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 3.

5. 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, the positioning system comprising an XY direction positioning module and a Z direction positioning module, the XY direction positioning module and the Z direction positioning module respectively comprising a projection unit and a light receiving unit; A high-speed camera shooting system for recording corneal deformation images during the corneal deformation process; and The non-contact tonometer measurement system according to claim 4.

6. The non-contact tonometer according to claim 5, wherein: The projection unit of the XY direction positioning module includes multiple groups of light sources, apertures and lenses, which are fixed symmetrically along the 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.

7. The non-contact tonometer according to claim 5, wherein: 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.

8. The non-contact tonometer according to claim 5, wherein: 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.

9. 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 3 is implemented.

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