Cornea biomechanical property measuring method

Abstract

The invention relates to a cornea biomechanical property measurement method. The method comprises the following steps: acquiring pressure data, measurement data and video data in a cornea compression process; determining an adjustment value according to the video data; determining whether the measurement data satisfies a measurement precision condition according to the adjustment value; if the measurement precision condition is met, the cornea biomechanical property is measured according to the pressure data and the measurement data. According to the method, the precision of the measurement data can be judged according to the adjustment value determined according to the video data, the cornea biomechanical property is measured according to the pressure data and the measurement data only after the precision meets the measurement precision condition, and accurate measurement of the cornea biomechanical property is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of biomechanics, and in particular to a method for measuring the biomechanical properties of cornea. Background Art

[0002] Corneal elasticity reflects the ability of the cornea to protect the cornea against intraocular pressure, and plays an important role in maintaining corneal shape and transparency, designing refractive surgery, and developing artificial corneas. Many pathological conditions of the cornea are closely related to its elasticity, especially corneal ectasia diseases, such as keratoconus, corneal marginal degeneration, and iatrogenic corneal ectasia after laser in situ keratomileusis.

[0003] Understanding corneal elasticity is of great reference value for the diagnosis and treatment of corneal diseases. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In order to solve the above problems, the present invention provides a method for measuring corneal biomechanical properties.

[0006] (II) Technical solution

[0007] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0008] A method for measuring corneal biomechanical properties, the method comprising:

[0009] Collect pressure data, measurement data and video data of the corneal compression process;

[0010] determining an adjustment value based on the video data;

[0011] Determine whether the measurement data meets the measurement accuracy condition according to the adjustment value;

[0012] If the measurement accuracy conditions are met, the corneal biomechanical properties are measured based on the pressure data and the measurement data.

[0013] Optionally, determining the adjustment value according to the video data includes:

[0014] Split the video data into multiple frames of images, and sort the multiple frames of images from far to near according to the acquisition time to obtain an image sequence;

[0015] Extracting a compressed subsequence and a recovered subsequence from the image sequence;

[0016] A compression parameter is obtained based on the compression subsequence, and a recovery parameter is obtained based on the recovery subsequence;

[0017] The adjustment value is determined based on the stress parameter and the recovery parameter.

[0018] Optionally, extracting a compressed subsequence and a restored subsequence from the image sequence includes:

[0019] Determine the corneal contour of each frame image in the image sequence;

[0020] Determine the coordinates of the center point of the corneal central area in each frame of image according to the corneal contour;

[0021] Starting from the first frame of the image sequence, compare the coordinate difference of the center point between it and the next frame of the image;

[0022] When a frame image Im appears for the first time y0 , the center point coordinate difference is greater than the preset coordinate difference threshold, and Im y0 If the coordinate differences of the center points of the first preset number of consecutive frames of images are greater than the preset coordinate difference threshold, then Im y0 As the first frame image of the compressed subsequence;

[0023] When Im y0 After that, a frame of image Im appears for the first time y1 , the center point coordinate difference is not greater than the preset coordinate difference threshold, and Im y1 If the coordinate differences of the center points of the second preset number of consecutive frames of images are not greater than the preset coordinate difference threshold, then Im y1 As the last frame image of the compressed subsequence;

[0024] When Im y1 After that, a frame of image Im appears for the first time y2 , the center point coordinate difference is greater than the preset coordinate difference threshold, and Im y2 If the coordinate differences of the center points of the third preset number of consecutive frames of images are greater than the preset coordinate difference threshold, then Im y2 As the first frame image of the restored subsequence;

[0025] When Im y2 After that, a frame of image Im appears for the first time y3 , the center point coordinate difference is not greater than the preset coordinate difference threshold, and Im y3 If the coordinate differences of the center points of the fourth preset number of consecutive frames of images are not greater than the preset coordinate difference threshold, then Im y3 As the last frame image of the restored subsequence.

[0026] Optionally, the pressure parameter and the recovery parameter both include duration, corneal displacement difference sequence, and maximum displacement difference;

[0027] The compression parameters are obtained based on the compression subsequence, including:

[0028] Determine the acquisition time of the first frame of the compressed subsequence and the acquisition time of the last frame of image Where I is the total number of images in the compressed subsequence;

[0029] Determine the position of the cornea in each frame of the compressed subsequence Where i is the image identifier in the compressed subsequence;

[0030] Determine the position difference between two adjacent frames of the compressed subsequence

[0031] Determine the duration of the stress parameter The corneal displacement difference sequence is Maximum displacement difference

[0032] The recovery parameters are obtained based on the recovery subsequence, including:

[0033] Determine the acquisition time of the first frame of the restored subsequence and the acquisition time of the last frame of image Where J is the total number of images in the restored subsequence;

[0034] Determine the position of the cornea in each frame of the restored subsequence Where j is the image identifier in the restored subsequence;

[0035] Determine the position difference between two adjacent frames of the restored subsequence

[0036] Determine the duration in the recovery parameters The corneal displacement difference sequence is Maximum displacement difference

[0037] Optionally, determining the adjustment value according to the pressure parameter and the recovery parameter includes:

[0038] In the image sequence, the xth d +1 frame image to the xth u -1 frame images form an adjustment subsequence; where x d is the sequence number of the last frame of the compressed subsequence in the image sequence, x u To restore the sequence number of the first frame image in the subsequence in the image sequence;

[0039] Determine the acquisition time of the first frame of the adjustment subsequence and the acquisition time of the last frame of image Where K is the total number of images in the adjusted subsequence;

[0040] Determine the standard value S of the pressure process according to the pressure parameters d, determine the standard value S of the recovery process according to the recovery parameters u ;

[0041] Determine the maximum corneal displacement S based on the measured data 0 ;

[0042] According to S 0 , S d , S u Determine the adjustment value.

[0043] Optionally,

[0044]

[0045] Among them, α is the acquisition time difference between two adjacent frames in the image sequence, and θ is the time length when the cornea stops deforming when it reaches the maximum depression.

[0046] Optionally, according to S 0 , S d , S u Determine the adjustment value, including:

[0047] Determine the first difference β 1 =|S d -S u |, the second difference β 2 =|S 0 -S u |, the third difference β 3 =|S 0 -S d |;

[0048] Determine the mean difference and standard deviation

[0049] Determine the adjustment value

[0050] Optionally, determining whether the measurement data meets the measurement accuracy condition according to the adjustment value includes:

[0051] Determine CD d The mean μ of all elements in d and standard deviation σ d , confirm CD u The mean μ of all elements in d and standard deviation σ u ;

[0052] According to μ d , σ d , μ d , σ u Determine the maximum value for adjustment;

[0053] If the adjustment value is not greater than the adjustment maximum value, it is determined that the measurement data meets the measurement accuracy condition.

[0054] Optionally, according to μ d , σ d , μ d , σ u Determine the maximum adjustment, including:

[0055] Determine the maximum value of the adjustment

[0056] Among them, AD 0 is the preset accuracy threshold.

[0057] Optionally, collecting pressure data and measurement data of the corneal compression process includes:

[0058] While controlling the indenter to press against the cornea and emitting ultrasonic waves to the cornea, the mechanical sensor measures the pressure data on the cornea in real time and receives the echo data reflected by the cornea.

[0059] (III) Beneficial effects

[0060] The present invention relates to a method for measuring corneal biomechanical properties, the method comprising: collecting pressure data, measurement data and video data of a corneal compression process; determining an adjustment value according to the video data; determining whether the measurement data meets a measurement accuracy condition according to the adjustment value; if the measurement accuracy condition is met, measuring the corneal biomechanical properties according to the pressure data and the measurement data. The method of the present invention can judge the accuracy of the measurement data by the adjustment value determined according to the video data, and only after the accuracy meets the measurement accuracy condition, measure the corneal biomechanical properties according to the pressure data and the measurement data, thereby achieving accurate measurement of the corneal biomechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 A schematic diagram of a method for measuring corneal biomechanical properties provided in one embodiment of the present application;

[0062] Figure 2 A schematic diagram of the structure of a pressure data and measurement data acquisition device provided in one embodiment of the present application;

[0063] Figure 3 A schematic diagram of an image of video data provided by an embodiment of the present application;

[0064] Figure 4 A schematic diagram of the structure of a corneal indentation device provided in one embodiment of the present application;

[0065] Figure 5A schematic diagram of the corneal contour pressure change provided in one embodiment of the present application. DETAILED DESCRIPTION

[0066] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0067] Corneal elasticity reflects the ability of the cornea to protect the cornea against intraocular pressure, and plays an important role in maintaining corneal shape and transparency, designing refractive surgery, and developing artificial corneas. Many pathological conditions of the cornea are closely related to its elasticity, especially corneal ectasia diseases, such as keratoconus, corneal marginal degeneration, and iatrogenic corneal ectasia after laser in situ keratomileusis. Understanding corneal elasticity is of great reference value for the diagnosis and treatment of corneal diseases.

[0068] In order to measure the biomechanical properties of the cornea, the present invention provides a method, which includes: collecting pressure data, measurement data and video data of the cornea being compressed; determining an adjustment value according to the video data; determining whether the measurement data meets the measurement accuracy condition according to the adjustment value; if the measurement accuracy condition is met, measuring the biomechanical properties of the cornea according to the pressure data and the measurement data. The method of the present invention can judge the accuracy of the measurement data by the adjustment value determined according to the video data, and only when the accuracy meets the measurement accuracy condition, measure the biomechanical properties of the cornea according to the pressure data and the measurement data, thereby achieving accurate measurement of the biomechanical properties of the cornea.

[0069] See also Figure 1 The implementation process of the corneal biomechanical property measurement method provided in this embodiment is as follows:

[0070] 101, collecting pressure data, measurement data and video data of the corneal compression process.

[0071] Among them, pressure data and measurement data can be obtained by controlling the indenter to press against the cornea and transmitting ultrasonic waves to the cornea, and the pressure data on the cornea can be measured in real time through the mechanical sensor, and the echo data reflected by the cornea can be received. Video data can be collected by a high-precision camera.

[0072] The measurement data collection process can be achieved through existing collection equipment, such as Figure 2 The device shown collects pressure data and measurement data, and a high-precision camera is set up perpendicular to the side of the eye to collect Figure 3 The video data shown.

[0073] Figure 2In the figure, 4 is a corneal indentation device, 6 is a ring-shaped point light source composed of multiple LEDs, 7 is a dichroic mirror, 8 is a converging lens, 9 is an image acquisition CCD (Charge Coupled Device) device, and 18 is an OCT (Optical Coherence Tomography) measuring device.

[0074] 10 is a scanning mirror, 11 is a focusing mirror, 12 is a polarization controller, 13 is a coupler, 14 is a movable reflector, 15 is a collimating mirror, 16 is a weak coherent light source, and 17 is a differential detection device.

[0075] The dichroic beam splitter 7 couples the OCT measuring device 18 and the image acquisition CCD device.

[0076] The corneal impression device 4 can be as follows Figure 4 As shown, it includes an indenter 19, and its function is: initially, the indenter 19 contacts the apex of the cornea, and then the indenter device drives the indenter 19 to indent the cornea. The cornea is subjected to inward pressure and is recessed backward. After the pressure is transmitted through a support rod 20 with a fixed support point 21, the pressure on the cornea is detected by a mechanical sensor 22 to obtain pressure data.

[0077] The indenter 19 is a transparent device that allows OCT light to pass through and measure the deformation of the cornea. The OCT light can be static as a single point or can be scanned to measure the structure and deformation of the cornea. The indenter 19 can also be an ultrasonic sensor probe. In this case, the ultrasonic sensor is the indenter that presses the cornea and can measure the corneal structure and deformation.

[0078] The annular point light source 6 emits an annular dot matrix light spot to illuminate the corneal surface. After the light spot is reflected by the cornea, it passes through the dichroic mirror 7 and is focused by the converging lens 8 to the image acquisition CCD device 9, so that a distribution image of the light spot on the cornea can be obtained, which is the measurement data.

[0079] The OCT measuring device 18 can measure the structure and displacement of the cornea, wherein the OCT measuring device 18 can adopt a structure well known to those skilled in the art. The OCT measuring device 18 uses the basic principle of weak coherent light interferometer to detect the back reflection or several scattering signals of the incident weak coherent light at different depths of biological tissues, and can obtain a two-dimensional or three-dimensional structural image of the cornea by scanning, and the two-dimensional or three-dimensional structural image of the cornea is also the measurement data.

[0080] In addition, a weak coherent light source 16 is used as a detection light source; the light it emits is divided into two beams by a coupler 13, entering the reference arm and the sample arm respectively, and then returning to the coupler 13 after being reflected by the reference arm and the sample arm; wherein, a collimator 15 and a movable reflector 14 constitute the reference arm optical path; a polarization controller 12, a scanning mirror 10, a converging mirror 11, a dichroic mirror 7 and an indenter 19 constitute the sample arm optical path; a differential detection device 17 obtains the signal returned by the reference arm and the sample arm after interference in the coupler, and the signal is also the measurement data.

[0081] For example, a detection light is emitted by a weak coherent light source 16, which is split by a coupler 13 and enters a reference arm and a sample arm respectively. The detection light is focused by a converging mirror 11 and is reflected by a scanning mirror 10 and a dichroic mirror 7 and transmitted by an indenter 19 before being converged onto the cornea. The return light 12 carrying information on the structure of the cornea and the anterior segment of the eye interferes with the reflected light from the reference arm. The interference signal passes through the coupler 13 and is detected by a differential detector 17 to obtain a signal after interference.

[0082] Among them, the weak coherent light source 16 can be a near-infrared SLED light source with a central wavelength of 1310nm and a maximum optical power of 5mW. The coupler 13 can be a 2*2 port fiber coupler, which can further divide the light incident from one port into two beams of outgoing light; or the light from the two ports can be coupled together and then emitted from the other two ports. The reference arm part can realize the longitudinal scanning of the cornea by the OCT system through the movable reflector 14. The differential detection device 17 realizes differential input amplification of the optical signals with opposite phases through photoelectric conversion, thereby obtaining OCT information with corneal structure.

[0083] The indenter 19 can be an ultrasonic probe, that is, it can be used as an indenter to indent the cornea (wherein the indentation range is 0.2mm-1.5mm), and at the same time, it can be used as a detection device for corneal structure and deformation. If the OCT measuring device 18 is replaced by an ultrasonic device, the ultrasonic device is installed at the center of the indenter 19, and the indenter 19 and the CCD device 9 can monitor and align the cornea in real time through the converging lens, the annular point light source 6, and the indenter 19.

[0084] The collection process is:

[0085] 1) Use the indenter to press against the cornea; transmit the OCT detection signal to the cornea in real time through the indenter, and receive the OCT reflection signal reflected back from the cornea.

[0086] 2) During the entire process of the stamping head pressing against the cornea, the mechanical sensor 22 measures the pressure exerted on the cornea in real time and collects measurement data. At the same time, a high-precision camera collects video data.

[0087] The measurement data include but are not limited to: the distribution image of the light spot on the cornea focused by the converging lens 8 onto the image acquisition CCD device 9; the two-dimensional or three-dimensional structural image of the cornea obtained by the OCT measurement device 18; the signal returned by the reference arm and the sample arm after the coupler interference and the OCT information of the corneal structure obtained by the differential detection device 17.

[0088] It should be noted that video data is only used to verify the accuracy of pressure data and measurement data, and does not participate in the actual measurement of the biomechanical properties of the cornea. Therefore, the high-precision camera that collects video data only needs to capture the side of the cornea, and does not require the shooting angle to meet a preset value. However, during the entire collection process, the position and parameters of the high-precision camera and cornea cannot change.

[0089] 102, determining an adjustment value according to the video data.

[0090] The implementation process of step 102 is:

[0091] 102-1, split the video data into multiple frames of images, and sort the multiple frames of images from far to near according to the acquisition time to obtain an image sequence.

[0092] 102-2, extracting a compressed subsequence and a restored subsequence from the image sequence.

[0093] The pressure subsequence is a sequence of frame images corresponding to the process of corneal pressure when the indenter is pressed against the cornea. The recovery subsequence is a sequence of frame images corresponding to the process of corneal rebounding due to the gradual decrease of pressure during the recovery process after the indenter is pressed.

[0094] The implementation process of step 102-2 is:

[0095] 1. Determine the corneal contour of each frame in the image sequence.

[0096] This step may adopt an existing image recognition method to determine the corneal contour of each frame image in the image sequence.

[0097] Because the position and parameters of the high-precision camera and cornea do not change during the video data acquisition process, the overall position of the cornea does not change in each frame of the image, but the contour of the compressed deformation will change, such as Figure 5 The diagram shows the change of corneal contour under pressure, where (a) is the corneal contour when there is no pressure, (b) is the corneal contour when there is pressure but not maximum depression, and (c) is the corneal contour when there is maximum depression.

[0098] 2. Determine the coordinates of the center point of the central area of ​​the cornea in each frame of the image based on the corneal contour.

[0099] Since the overall position of the cornea is fixed in each frame image, the center point of the corneal contour can be identified in the first frame image in the image sequence, such as Figure 5 (a) Point A, determine the coordinates of point A in the pixel coordinate system (such as the upper left corner of the image is the origin of the pixel coordinate system, the horizontal direction of the image is the x-axis of the pixel coordinate system, the right is the positive direction of the x-axis, the vertical direction of the image is the y-axis of the pixel coordinate system, and the downward direction is the positive direction of the y-axis). During the corneal compression process, the ordinate value of point A in the pixel coordinate system remains unchanged, while the abscissa value changes. Then, based on the ordinate value of point A, determine the point in the corneal contour with the ordinate value in other frames of images. This point is the center point of the frame image, and the coordinates of this point are the coordinates of the center point.

[0100] 3. Starting from the first frame of the image sequence, compare the coordinate difference of the center point between it and the next frame.

[0101] Because the vertical coordinate of the center point of each frame does not change, the coordinate difference is actually the horizontal coordinate difference, that is, the distance that the center point is depressed.

[0102] 4. When a frame appears for the first time The center point coordinate difference is greater than the preset coordinate difference threshold, and If the coordinate differences of the center points of the first preset number of consecutive frames of images are greater than the preset coordinate difference threshold, As the first frame image of the compressed subsequence.

[0103] For example, if the first preset number is 5, then The coordinate differences of the center points of the following four consecutive frames of images are all greater than a preset coordinate difference threshold, which is 0 or 3.

[0104] The following example takes the preset coordinate difference threshold value = 0 and the first preset number = 5, because the video data is collected along with the process of the indentation head 19 indenting the cornea, and the process of the indentation head 19 indenting the cornea cannot ensure that the first frame of the video data is the beginning of the pressing. For example, if the pressure is applied 2 seconds after the start of the pressing, the center point of the corneal contour in the video data 2 seconds ago does not change, but the pressed subsequence starts from the first frame of the pressure application, so the coordinate difference of the center point of two adjacent frames will be compared.

[0105] For example, starting from the first frame of the image sequence, the coordinate difference between the center point of the second frame and the first frame is 0, the coordinate difference between the center point of the third frame and the second frame is 0, which means that the cornea is not under pressure at this time, the coordinate difference between the center point of the fourth frame and the third frame is 0, and so on. Frame and If the coordinate difference of the center point of the frame is 3, it is very likely that the cornea is under pressure at this time.

[0106] In practical applications, the coordinate difference of the center point may be non-zero due to inevitable jitter. Afterwards, Frame and The coordinate difference of the center point of the frame is non-zero. Frame and The coordinate difference of the center point of the frame is non-zero, .... If If the error is not zero for 5 consecutive frames, it means that it is not caused by accidental jitter. As the first frame image of the compressed subsequence.

[0107] 5. When After that, a frame of image appears for the first time The coordinate difference of the center point is not greater than the preset coordinate difference threshold, and If the coordinate difference of the center point of the second preset number of consecutive frames of images is not greater than the preset coordinate difference threshold, As the last frame of the compressed subsequence.

[0108] When the cornea reaches the maximum depression, it will maintain a certain contour, that is, the first frame of the image appears The coordinate difference of the center point is not greater than the preset coordinate difference threshold, and If the coordinate difference of the center point of the second preset number of consecutive frames of images is not greater than the preset coordinate difference threshold, it is considered that the cornea has reached the maximum depression, that is, the compression process is completed, then As the last frame of the compressed subsequence.

[0109] Taking the preset coordinate difference threshold = 0 and the second preset number = 3 as an example, Afterwards, Frame and The coordinate difference of the center point of the frame is non-zero, but Frame and The coordinate difference of the center point of the frame is zero. Frame and The coordinate difference of the center point of the frame is zero. Frame and The coordinate difference of the center point of the frame is zero, so it is considered It is the last frame image of the compressed subsequence.

[0110] from to The frame images between form a compressed subsequence, where the compressed subsequence contains and

[0111] 6. When After that, a frame of image appears for the first time The center point coordinate difference is greater than the preset coordinate difference threshold, and If the coordinate differences of the center points of the three consecutive preset number of frames of images are greater than the preset coordinate difference threshold, As the first frame image of the restored subsequence.

[0112] 7. When After that, a frame of image appears for the first time The coordinate difference of the center point is not greater than the preset coordinate difference threshold, and If the coordinate difference of the center point of the fourth preset number of consecutive frames of images is not greater than the preset coordinate difference threshold, As the last frame image of the restored subsequence.

[0113] The same principle applies to Afterwards, if the center point coordinate difference is greater than the preset coordinate difference threshold again, the recovery process is entered, and if the center point coordinate difference is not greater than the preset coordinate difference threshold again, the recovery process is completed. This process is the reverse process of the compression process, and can be referred to the extraction process of the compression subsequence in the compression process above, which will not be explained in detail here.

[0114] In addition, since the high-precision camera acquisition angle is not limited, it is possible that the image of the standard corneal contour reaching the maximum depression will not be collected due to occlusion, such as being blocked by the edge of the corneal contour. For example, the entire pressing process is 7 seconds, of which 1 second to 3 seconds is the compression process, 4 seconds reaches the maximum depression, and 5 seconds to 7 seconds is the recovery process. However, in the video data, the corneal contour does not change from the data of the 2nd second (because it is blocked by the corneal edge, the center point can no longer be seen in the image, so the position of the center point no longer changes) until it starts to change again at the 6th second. At this time, the compression subsequence is a sequence composed of image data of 1 second and 2 seconds, and the recovery subsequence is a sequence composed of image data of 6 seconds and 7 seconds. Then the sequence composed of image data between 3 seconds and 5 seconds is the adjustment subsequence. In the adjustment subsequence, although the corneal contour has not changed, the actual cornea has experienced a process of partial compression-reaching the maximum depression-partial recovery.

[0115] 102-3, obtaining a compression parameter based on the compression subsequence, and obtaining a recovery parameter based on the recovery subsequence.

[0116] The pressure parameter and the recovery parameter both include duration, corneal displacement difference sequence, and maximum displacement difference. That is, the pressure parameter and the recovery parameter include the same parameter items, but the value of each parameter item is different.

[0117] 1. The process of obtaining the pressure parameters based on the pressure subsequence is:

[0118] 211, determine the acquisition time of the first frame image of the pressure subsequence and the acquisition time of the last frame of image

[0119] Where I is the total number of images in the compressed subsequence.

[0120] 212, determining the position of the cornea in each frame image of the pressure subsequence

[0121] Where i is the image identifier in the compressed subsequence. It can be the coordinates of the center point of the central area of ​​the cornea in each frame image, or the horizontal coordinates of the center point of the central area of ​​the cornea in each frame image.

[0122] 213, determine the position difference between two adjacent frames of the compressed subsequence

[0123] It can be the horizontal coordinate difference of the central point of the central area between two adjacent frames of images. This value is actually the distance that the central point of the central area is depressed due to the pressure of the printing head.

[0124] 214, Determine the duration of the stress parameter The corneal displacement difference sequence is Maximum displacement difference

[0125] 2. The process of obtaining the recovery parameters based on the recovery subsequence is:

[0126] 221, determine the acquisition time of the first frame image of the recovery subsequence and the acquisition time of the last frame of image

[0127] Where J is the total number of images in the restored subsequence.

[0128] 222, determine the position of the cornea in each frame image of the restored subsequence

[0129] Among them, j is the image identifier in the restored subsequence. It can be the coordinates of the center point of the central area of ​​the cornea in each frame image, or the horizontal coordinates of the center point of the central area of ​​the cornea in each frame image.

[0130] 223, determine the position difference between two adjacent frames of the restored subsequence

[0131] It can be the horizontal coordinate difference of the central point of the central area between two adjacent frames of images. This value is actually the distance restored by the central point of the central area due to the gradual reduction of the pressure from the printing head.

[0132] 224, Determine the duration of the recovery parameters The corneal displacement difference sequence is Maximum displacement difference

[0133] 102-4, determining an adjustment value according to the pressure parameter and the recovery parameter.

[0134] The implementation process of this step is:

[0135] 1. In the image sequence, place the xth d +1 frame image to the xth u The consecutive frame images between -1 frame images form an adjustment subsequence.

[0136] Among them, x d is the sequence number of the last frame of the compressed subsequence in the image sequence, x u To restore the sequence number of the first frame image in the subsequence in the image sequence.

[0137] Since the high-precision camera acquisition angle is not limited, it is possible that the image of the standard corneal contour reaching the maximum depression will not be collected due to occlusion, such as being blocked by the edge of the corneal contour. For example, the entire pressing process is 7 seconds, of which 1 second to 3 seconds is the compression process, 4 seconds reaches the maximum depression, and 5 seconds to 7 seconds is the recovery process. However, in the video data, the corneal contour does not change from the data of the 2nd second (because it is blocked by the edge of the cornea, the center point can no longer be seen in the image, so the position of the center point no longer changes) until it starts to change again at the 6th second. At this time, the compression subsequence is a sequence composed of image data of 1 second and 2 seconds, and the recovery subsequence is a sequence composed of image data of 6 seconds and 7 seconds. Then the sequence composed of image data between 3 seconds and 5 seconds is the adjustment subsequence. In the adjustment subsequence, although the corneal contour has not changed, the actual cornea has experienced a process of partial compression-reaching maximum depression-partial recovery.

[0138] 2. Determine the acquisition time of the first frame of the adjustment subsequence and the acquisition time of the last frame of image

[0139] Where K is the total number of images in the adjusted subsequence.

[0140] 3. Determine the standard value S of the pressure process according to the pressure parameters d , determine the standard value S of the recovery process according to the recovery parameters u .

[0141] For example,

[0142]

[0143] Among them, α is the acquisition time difference between two adjacent frames in the image sequence, and θ is the time length for the cornea to stop deforming when it reaches maximum depression (this value can be set comprehensively based on the pressure applied and the average time for the cornea to stop deforming. The average time for the cornea to stop deforming can be obtained in advance by testing a large number of corneas).

[0144] Below is S d Take the example to explain the characterization of each parameter. u The parameter characterization of S d That’s it, no further explanation is needed.

[0145] The moving speed of the center point during the compression process is characterized from the angle that can be monitored by the video data, and this speed is used as the maximum possible moving speed of the cornea during the compression process. It represents the average moving distance between two adjacent frames. The moving speed of the center point during the compression process is characterized from the perspective of the frame, and this speed is used as the most likely moving speed of the cornea during the compression process. The minimum moving speed of the center point during the compression process is characterized from the perspective of the frame, and this speed is used as the minimum possible moving speed of the cornea during the compression process. Characterizes the average velocity during the entire corneal compression process. Δt d The total duration of the compression process is characterized from the perspective of what the video data can monitor. Since there may be processes that are not monitored by the video data, that is, Characterizes the total duration of the stress process that was not monitored. It represents the total duration of the entire compression process. d It characterizes the displacement of the cornea during the entire compression process.

[0146] S u It characterizes the displacement of the cornea during the entire recovery process.

[0147] 4. Determine the maximum corneal displacement S based on the measured data 0 .

[0148] This value can be obtained through the interference signal and the two-dimensional or three-dimensional structure image of the cornea, and is the actual measurement value.

[0149] 5. According to S 0 , S d , S u Determine the adjustment value.

[0150] S 0 is the displacement of the cornea measured based on the measurement data, S d , S uIt is the displacement of the cornea calculated from the video data.

[0151] According to S 0 , S d , S u The process of determining the adjustment value is as follows: determining the first difference β 1 =|S d -S u |, the second difference β 2 =|S 0 -S u |, the third difference β 3 =|S 0 -S d |. Determine the mean difference and standard deviation Determine the adjustment value

[0152] The first difference, the second difference and the third difference represent the differences between the three corneal displacements. Characterizes the degree of change between these three differences.

[0153] If the degree of change is small, it means that the difference may be caused by the systematic error of different measurement processes and has nothing to do with the accuracy of the test data. If the degree of change is large, it means that the test data may be inaccurate.

[0154] 103 , determining whether the measurement data meets the measurement accuracy condition according to the adjustment value.

[0155] The implementation process of step 103 is:

[0156] 103-1, confirm CD d The mean μ of all elements in d and standard deviation σ d , confirm CD u The mean μ of all elements in u and standard deviation σ u .

[0157] 103-2, according to μ d , σ d , μ u , σ u Determines the maximum value for adjustment.

[0158] The maximum value is adjusted to

[0159] Among them, AD 0 is the preset accuracy threshold.

[0160] is the degree of change obtained during the compression process, AD is the degree of change obtained during the recovery process. 0 The degree of change is set according to the measurement accuracy.

[0161] 103-3, if the adjustment value is not greater than the maximum adjustment value, it is determined that the measurement data meets the measurement accuracy condition.

[0162] If the adjustment value is not greater than the maximum adjustment value, it means that the difference may be caused by the system error of different measurement processes and has nothing to do with the accuracy of the test data, so it is determined that the measurement data meets the measurement accuracy condition. Otherwise, it means that the test data may be inaccurate, and the execution of the corneal biomechanical property measurement method provided in this embodiment can be terminated, and an early warning can be issued so that the measurement can be performed again.

[0163] 104. If the measurement accuracy condition is met, the biomechanical properties of the cornea are measured according to the pressure data and the measurement data.

[0164] This step can be implemented using existing solutions.

[0165] For example, the measurement data includes but is not limited to: the distribution image of the light spot on the cornea focused by the converging lens 8 onto the image acquisition CCD device 9; the two-dimensional or three-dimensional structural image of the cornea obtained by the OCT measurement device 18; the signal returned by the reference arm and the sample arm after the coupler interference and the OCT information of the corneal structure obtained by the differential detection device 17.

[0166] The biomechanical properties of the cornea include but are not limited to: corneal curvature information; corneal structure; corneal displacement; OCT information of corneal structure; position information of the anterior and posterior surfaces of the cornea and the anterior surface of the lens; corneal thickness; corneal elastic modulus; corneal Poisson's ratio; and intraocular pressure.

[0167] For example, curvature information is determined by analyzing the distribution image of the light spot on the cornea. The corneal curvature is calculated using the spherical mirror imaging method. The cornea can be approximated as a spherical reflector with a curvature radius of r and a focal length of f. The LED light spot h is reflected by the cornea to form an image h', the distance between the light spot h and the image h' is d, and the distance from the light spot h to the corneal focus is CFD. The imaging formula can be obtained:

[0168] Usually, for a spherical mirror Since the radius of curvature of the cornea is much smaller than the working distance, CFD = d, and thus, the radius of curvature of the cornea is

[0169] The structure and displacement of the cornea can be obtained based on the interference signal and the two-dimensional or three-dimensional structural image of the cornea.

[0170] The OCT image of the longitudinal structure of the cornea can determine the position information of the anterior and posterior surfaces of the cornea and the anterior surface of the lens.

[0171] The thickness of the cornea TH can be obtained by measuring the longitudinal structure information of the cornea using OCT. The thickness TH is the distance difference between the front and back surfaces of the cornea. The deformation of the cornea is calculated by measuring the displacement of the cornea relative to the front surface of the lens during the indentation process, or by calculating the indentation distance.

[0172] The elastic modulus (Young's modulus) of the cornea is based on the Imbert-Fick principle. When the indenter contacts and indents the cornea, the calculation formula of the corneal elastic modulus can be derived according to the mechanical equilibrium model:

[0173]

[0174] Among them, r is the radius of curvature of the cornea, TH is the thickness of the cornea, υ is the Poisson's ratio of the cornea, F is the pressure on the cornea, δ is the displacement of the corneal depression, It represents the slope of the pressure-displacement curve, and a is the corneal geometric constant factor.

[0175] The cornea is generally considered to be a geometrically incompressible tissue, and the Poisson's ratio of the cornea is generally set to 0.45.

[0176] The corneal geometric constant factor a is related to corneal curvature, thickness, Poisson's ratio, indenter and corneal contact area. This relationship can be expressed by the formula reflect.

[0177] Among them, r 0 is the contact area between the indenter and the cornea.

[0178] Intraocular pressure (IOP) is the ratio of the pressure on the cornea to the area of ​​corneal flattening when the cornea is in a certain flattened state. The area of ​​corneal flattening can be calculated by OCT scanning the structure of the cornea, and the pressure is recorded by the mechanical sensor 22. Indenters 19 of different sizes can be used to indent the cornea to measure corneal elasticity or flatten the cornea to measure intraocular pressure.

[0179] The corneal biomechanical property measurement method provided in this embodiment collects pressure data, measurement data and video data of the corneal pressure process; determines the adjustment value according to the video data; determines whether the measurement data meets the measurement accuracy condition according to the adjustment value; if the measurement accuracy condition is met, the corneal biomechanical property is measured according to the pressure data and the measurement data. The method of this embodiment can judge the accuracy of the measurement data by the adjustment value determined according to the video data, and only when the accuracy meets the measurement accuracy condition, the corneal biomechanical property is measured according to the pressure data and the measurement data, thereby achieving accurate measurement of the corneal biomechanical property.

[0180] It should be clear that the present invention is not limited to the specific configuration and processing described above and shown in the figures. For the sake of simplicity, a detailed description of the known method is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present invention.

[0181] It should also be noted that the exemplary embodiments mentioned in the present invention describe some methods or systems based on a series of steps or devices. However, the present invention is not limited to the order of the above steps, that is, the steps can be performed in the order mentioned in the embodiments, or in a different order from the embodiments, or several steps can be performed simultaneously.

[0182] Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring corneal biomechanical properties, characterized in that: The method comprises: Collect pressure data, measurement data and video data of the corneal compression process; determining an adjustment value according to the video data; Determining whether the measurement data meets a measurement accuracy condition according to the adjustment value; If the measurement accuracy condition is met, the corneal biomechanical properties are measured based on the pressure data and the measurement data.

2. The method according to claim 1, characterized in that The determining the adjustment value according to the video data comprises: Splitting the video data into multiple frames of images, and sorting the multiple frames of images from far to near according to the acquisition time to obtain an image sequence; extracting a compressed subsequence and a restored subsequence from the image sequence; Obtaining a compression parameter based on the compression subsequence, and obtaining a recovery parameter based on the recovery subsequence; The adjustment value is determined based on the stress parameter and the recovery parameter.

3. The method according to claim 2, characterized in that The step of extracting a compressed subsequence and a restored subsequence from the image sequence comprises: Determine the corneal contour of each frame image in the image sequence; Determine the coordinates of the center point of the corneal central area in each frame of image according to the corneal contour; Starting from the first frame of the image sequence, compare the coordinate difference of the center point between it and the next frame of the image; When a frame appears for the first time The center point coordinate difference is greater than the preset coordinate difference threshold, and After the first preset number of consecutive frame image center point coordinate differences are greater than the preset coordinate difference threshold, As the first frame image of the compressed subsequence; when After that, a frame of image appears for the first time The coordinate difference of the center point is not greater than the preset coordinate difference threshold, and If the coordinate difference of the center point of the second preset number of consecutive frames of images is not greater than the preset coordinate difference threshold, As the last frame image of the compressed subsequence; when After that, a frame of image appears for the first time The center point coordinate difference is greater than the preset coordinate difference threshold, and If the coordinate differences of the center points of the three consecutive preset number of frames of images are greater than the preset coordinate difference threshold, As the first frame image of the restored subsequence; when After that, a frame of image appears for the first time The coordinate difference of the center point is not greater than the preset coordinate difference threshold, and If the coordinate difference of the center point of the fourth consecutive preset number of frames of images is not greater than the preset coordinate difference threshold, As the last frame image of the restored subsequence.

4. The method according to claim 2, characterized in that: The pressure parameters and recovery parameters include duration, corneal displacement difference sequence, and maximum displacement difference; The obtaining of the pressure parameter based on the pressure subsequence includes: Determine the acquisition time of the first frame image of the compressed subsequence and the acquisition time of the last frame of image Where, I is the total number of images in the compressed subsequence; Determine the position of the cornea in each frame image of the compressed subsequence Where i is the image identifier in the compressed subsequence; Determine the position difference between two adjacent frames of the compressed subsequence Determine the duration of the stress parameter The corneal displacement difference sequence is Maximum displacement difference The obtaining of the recovery parameter based on the recovery subsequence includes: Determine the acquisition time of the first frame image of the recovery subsequence and the acquisition time of the last frame of image Where J is the total number of images in the restored subsequence; Determine the position of the cornea in each frame image of the recovery subsequence Where j is the image identifier in the restored subsequence; Determine the position difference between two adjacent frames of the restored subsequence Determine the duration in the recovery parameters The corneal displacement difference sequence is Maximum displacement difference 5. The method according to claim 4, characterized in that Determining the adjustment value according to the pressure parameter and the recovery parameter includes: In the image sequence, the xth d +1 frame image to the xth u -1 frame images form an adjustment subsequence; where x d is the sequence number of the last frame of the compressed subsequence in the image sequence, x u To restore the sequence number of the first frame image in the subsequence in the image sequence; Determine the acquisition time of the first frame image of the adjustment subsequence and the acquisition time of the last frame of image Where K is the total number of images in the adjusted subsequence; Determine the standard value S of the pressure process according to the pressure parameters d , determine the standard value S of the recovery process according to the recovery parameters u ; Determine the maximum displacement S of the cornea according to the measurement data 0 ; According to S 0 , S d , S u Determine the adjustment value.

6. The method according to claim 5, characterized in that Wherein, α is the acquisition time difference between two adjacent frames in the image sequence, and θ is the time length for the cornea to stop deforming when reaching the maximum depression.

7. The method according to claim 5, characterized in that According to S 0 , S d , S u Determine the adjustment value, including: Determine the first difference β1 = |S d -S u |, the second difference β2 = |S 0 -S u |, the third difference β3 = |S 0 -S d |; Determine the mean difference and standard deviation Determine the adjustment value 8. The method according to claim 4, characterized in that The determining, according to the adjustment value, whether the measurement data meets the measurement accuracy condition includes: Determine CD d The mean μ of all elements in d and standard deviation σ d , confirm CD u The mean μ of all elements in u and standard deviation σ u ; According to μ d , σ d , μ u , σ u Determine the maximum value for adjustment; If the adjustment value is not greater than the maximum adjustment value, it is determined that the measurement data meets the measurement accuracy condition.

9. The method according to claim 8, characterized in that According to μ d , σ d , μ u , σ u Determine the maximum adjustment, including: Determine the maximum value of the adjustment Among them, AD 0 is the preset accuracy threshold.

10. The method according to claim 1, characterized in that Collect pressure data and measurement data of the corneal compression process, including: While controlling the indenter to press against the cornea and emitting ultrasonic waves to the cornea, the mechanical sensor measures the pressure data on the cornea in real time and receives the echo data reflected by the cornea.

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