A method for measuring corneal biomechanical properties

Abstract

The present invention relates to a method for measuring corneal biomechanical properties. The method includes: collecting pressure data, measurement data, and video data during the process of corneal compression; 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 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 through the adjustment value determined according to the video data. Only after the accuracy meets the measurement accuracy condition, the corneal biomechanical properties are measured according to the pressure data and the measurement data, realizing the accurate measurement of the corneal biomechanical properties.

Description

Technical Field

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

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

[0003] Understanding corneal elasticity has important reference value for the diagnosis and treatment of corneal diseases. Summary of the Invention

[0004] (1) Technical Problems to be Solved

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

[0006] (2) Technical Solutions

[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] Collecting pressure data, measurement data, and video data during the process of the cornea being pressed;

[0010] Determining an adjustment value according to the video data;

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

[0012] If the measurement accuracy condition is met, measuring the corneal biomechanical properties according to the pressure data and the measurement data.

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

[0014] Splitting the video data into multiple frames of images, sorting 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 recovery subsequence from the image sequence;

[0016] Obtaining a compression parameter based on the compression subsequence and a recovery parameter based on the recovery subsequence;

[0017] Determining the adjustment value according to the compression parameter and the recovery parameter.

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

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

[0020] Determining the coordinates of the central point of the central corneal region in each frame image according to the corneal contour;

[0021] Starting from the first frame of the image sequence, comparing the difference in the coordinates of the central point between it and the subsequent frame image;

[0022] When for the first time there is a frame image Im y0 , the difference in the coordinates of its central point is greater than a preset coordinate difference threshold, and the differences in the coordinates of the central points of the first preset number of consecutive frame images after Im y0 are all greater than the preset coordinate difference threshold, then Im y0 is used as the first frame image of the compressed subsequence;

[0023] When after Im y0 , for the first time there is a frame image Im y1 , the difference in the coordinates of its central point is not greater than the preset coordinate difference threshold, and the differences in the coordinates of the central points of the second preset number of consecutive frame images after Im y1 are all not greater than the preset coordinate difference threshold, then Im y1 is used as the last frame image of the compressed subsequence;

[0024] When after Im y1 , for the first time there is a frame image Im y2 , the difference in the coordinates of its central point is greater than the preset coordinate difference threshold, and the differences in the coordinates of the central points of the third preset number of consecutive frame images after Im y2 are all greater than the preset coordinate difference threshold, then Im y2 is used as the first frame image of the recovery subsequence;

[0025] When after Im y2 , for the first time there is a frame image Im y3 , the difference in the coordinates of its central point is not greater than the preset coordinate difference threshold, and the differences in the coordinates of the central points of the fourth preset number of consecutive frame images after Im y3 are all not greater than the preset coordinate difference threshold, then Im y3 is used as the last frame image of the recovery subsequence.

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

[0027] Obtaining the compression parameter based on the compressed subsequence includes:

[0028] Determining the acquisition time of the first frame image of the compressed subsequence Wherein, I is the total number of images in the compressed subsequence;

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

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

[0031] Determine the duration in the compression parameter The corneal displacement difference sequence is The maximum displacement difference

[0032] Obtain the recovery parameter based on the recovery subsequence, including:

[0033] Determine the acquisition time of the first frame image of the recovery subsequence And the acquisition time of the last frame image Wherein, J is the total number of images in the recovery subsequence;

[0034] Determine the position of the cornea in each frame image of the recovery subsequence Wherein, j is the image identifier in the recovery subsequence;

[0035] Determine the position difference between two adjacent frame images of the recovery subsequence

[0036] Determine the duration in the recovery parameter The corneal displacement difference sequence is The maximum displacement difference

[0037] Optionally, determine the adjustment value according to the compression parameter and the recovery parameter, including:

[0038] In the image sequence, form an adjustment subsequence from the (x d + 1)-th frame image to the (x u - 1)-th frame image; wherein, x d is the serial number of the last frame image in the compressed subsequence in the image sequence, and x u is the serial number of the first frame image in the recovery subsequence in the image sequence;

[0039] Determine the acquisition time of the first frame image of the adjustment subsequence And the acquisition time of the last frame image Wherein, K is the total number of images in the adjustment subsequence;

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

[0041] Determine the maximum displacement S of the cornea according to the measurement 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 duration when the cornea stops deforming when reaching the maximum indentation.

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

[0047] 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 |;

[0048] Determine the average difference and the standard deviation

[0049] Determine the adjustment value as

[0050] Optionally, determine whether the measurement data meets the measurement accuracy conditions according to the adjustment value, including:

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

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

[0053] If the adjustment value is not greater than the adjustment maximum value, determine that the measurement data meets the measurement accuracy conditions.

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

[0055] Determine the adjustment maximum value as

[0056] wherein, AD 0 is a preset precision threshold.

[0057] Optionally, collect the pressure data and measurement data during the process of the cornea being pressed, including:

[0058] During the process of controlling the indenter to press against the cornea and emitting ultrasonic waves to the cornea, the pressure data received by the cornea is measured in real time through a mechanical sensor, and the echo data reflected by the cornea is received.

[0059] (III) Beneficial effects

[0060] The present invention relates to a method for measuring the biomechanical properties of the cornea. The method includes: collecting pressure data, measurement data and video data during the process of the cornea being pressed; 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, then measure 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 through the adjustment value determined according to the video data. Only after the accuracy meets the measurement accuracy condition, the biomechanical properties of the cornea are measured according to the pressure data and the measurement data, realizing the accurate measurement of the biomechanical properties of the cornea. Brief description of the drawings

[0061] Figure 1 is a schematic flowchart of a method for measuring the biomechanical properties of the cornea provided by an embodiment of the present application;

[0062] Figure 2 is a schematic structural diagram of a pressure data and measurement data acquisition device provided by an embodiment of the present application;

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

[0064] Figure 4 is a schematic structural diagram of a corneal indentation device provided by an embodiment of the present application;

[0065] Figure 5 is a schematic diagram of the change in the corneal contour under pressure provided by an embodiment of the present application. Detailed implementation manners

[0066] For better explaining the present invention for easy understanding, the present invention will be described in detail below in conjunction with the accompanying drawings through specific embodiments.

[0067] Corneal elasticity reflects the ability of the cornea to resist intraocular pressure and protect the cornea, and plays an important role in maintaining the corneal shape and transparency, the design of refractive surgery, the research and development of artificial corneas, etc. Many pathological states of the cornea are closely related to its elasticity, especially corneal ectasia diseases such as keratoconus, marginal corneal degeneration, and iatrogenic corneal ectasia after LASIK (Laser in Situ Keratomileusis). Understanding corneal elasticity has important reference value for the diagnosis and treatment of corneal diseases.

[0068] To measure the biomechanical properties of the cornea, the present invention provides a method, which includes: collecting pressure data, measurement data, and video data during the process of the cornea being pressed; 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, then measuring the biomechanical properties of the cornea according to the pressure data and the measurement data. The method involved in the present invention can judge the accuracy of the measurement data through the adjustment value determined according to the video data. Only after the accuracy meets the measurement accuracy condition, then measure the biomechanical properties of the cornea according to the pressure data and the measurement data, realizing the accurate measurement of the biomechanical properties of the cornea.

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

[0070] 101, collect pressure data, measurement data, and video data during the process of the cornea being pressed.

[0071] Among them, the pressure data and the measurement data can measure the pressure data received by the cornea in real time through a mechanical sensor during the process of controlling the indenter to press against the cornea and emitting ultrasonic waves to the cornea, and receiving the echo data reflected by the cornea. The video data can be collected by a high-precision camera.

[0072] The acquisition process of the measurement data can be realized by existing acquisition devices. For example, the pressure data and the measurement data are collected by the device shown in Figure 2 , and at the same time, a high-precision camera is erected perpendicular to the side of the eye to collect the Figure 3 shown video data.

[0073] Figure 2 In , 4 is a corneal indentation device, 6 is an annular point light source composed of multiple LEDs, 7 is a dichroic beam splitter, 8 is a converging lens, 9 is an image acquisition CCD (Charge Coupled Device) device, and 18 is an OCT (Optical Coherence Tomography) measurement device.

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

[0075] Among them, the dichroic beam splitter 7 couples the OCT measurement device 18 and the image acquisition CCD device.

[0076] The corneal indentation device 4 can be as Figure 4 shown, including an indentation head 19, whose function is: initially, the indentation head 19 contacts the corneal apex position, and then the indentation device drives the indentation head 19 to indent the cornea. The cornea is indented backward under the inward pressure, and the pressure received is transmitted through a support rod 20 with a fixed support point 21 and then detected by a mechanical sensor 22 to obtain the pressure borne by the cornea, that is, the pressure data.

[0077] The indentation head 19 is a transparent device that allows OCT light to pass through and measure the deformation of the cornea. The OCT light can be stationary as a single point or scanned to measure the structure and deformation of the cornea. The indentation head 19 can also be an ultrasonic sensor probe. In this case, the ultrasonic sensor not only indents the cornea but also measures the structure and deformation of the cornea.

[0078] Among them, the annular point light source 6 emits an annular dot matrix light spot that irradiates the corneal surface. After being reflected by the cornea, the light spot passes through the dichroic beam splitter 7 and is focused by the focusing lens 8 onto the image acquisition CCD device 9, so that the distribution image of the light spot on the cornea can be obtained, and this distribution image is the measurement data.

[0079] The OCT measurement device 18 can measure the structure and displacement of the cornea. Among them, the OCT measurement device 18 can adopt a structure well-known to those skilled in the art. The OCT measurement device 18 utilizes the basic principle of a low-coherence light interferometer to detect the backscattering or multiple scattering signals of incident low-coherence light by different depth layers of biological tissue. Through scanning, a two-dimensional or three-dimensional structure image of the cornea can be obtained, and this two-dimensional or three-dimensional structure image of the cornea is also the measurement data.

[0080] In addition, the low-coherence light source 16 as the detection light source; the light emitted by it is split into two beams by the coupler 13 and enters the reference arm and the sample arm respectively, and then returns to the coupler 13 after being reflected by the reference arm and the sample arm; among them, the collimating lens 15 and the movable mirror 14 form the reference arm optical path; the polarization controller 12, the scanning mirror 10, the focusing lens 11, the dichroic beam splitter 7 and the indentation head 19 form the sample arm optical path; the differential detection device 17 obtains the signal after interference in the coupler returned by the reference arm and the sample arm, and this signal is also the measurement data.

[0081] For example, detection light is emitted by the weak coherent light source 16. After being split by the coupler 13, it enters the reference arm and the sample arm respectively. The detection light is focused by the focusing lens 11, and after being reflected by the scanning mirror 10 and the dichroic beam splitter 7 and transmitted through the indentation head 19, it converges on the cornea. The return light 12 carrying corneal structure information and anterior segment information interferes with the reference arm reflected light, and the interference signal is detected by the differential detector 17 after passing through the coupler 13 to obtain the interfered signal.

[0082] Among them, the weak coherent light source 16 can adopt a near-infrared SLED light source with a central wavelength of 1310 nm and a maximum optical power of 5 mW. The coupler 13 can be a 2*2 port fiber coupler, which can split the light incident from one port into two outgoing light beams, or couple the light from two ports together and then emit it from the other two ports. The reference arm part can realize the longitudinal scanning of the cornea by the OCT system through the movable mirror 14. The differential detection device 17 performs photoelectric conversion on the optical signals with opposite phases to achieve differential input amplification, so as to obtain OCT information with corneal structure.

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

[0084] The acquisition process is as follows:

[0085] 1) Use the indentation head to press against the cornea; emit OCT detection signals to the cornea in real time through the indentation head and receive the OCT reflection signals reflected by the cornea.

[0086] 2) During the whole process of the indentation head pressing against the cornea, the mechanical sensor 22 measures the pressure on the cornea in real time. At the same time, measurement data is collected, and at the same time, video data is collected through a high-precision camera.

[0087] Among them, the measurement data includes but is not limited to: the distribution image of the light spot focused on the image acquisition CCD device 9 by the focusing lens 8 on the cornea; the two-dimensional or three-dimensional structure image of the cornea obtained by the OCT measurement device 18; the signal interfered by the reference arm and the sample arm in the coupler and the OCT information of the corneal structure obtained by the differential detection device 17.

[0088] It should be noted that the video data is only used to verify the accuracy of the pressure data and measurement data and does not participate in the actual measurement of the corneal biomechanical properties. Therefore, the high-precision camera for collecting video data only needs to be able to collect the side of the cornea, and there is no requirement that the shooting angle must meet a preset value. However, during the entire collection process, the position, parameters, etc. of the high-precision camera and the cornea cannot change.

[0089] 102. Determine the adjustment value according to the video data.

[0090] The implementation process of step 102 is as follows:

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

[0092] 102-2. Extract the compressed subsequence and the recovery subsequence from the image sequence.

[0093] Among them, the compressed subsequence is a sequence composed of the frame images corresponding to the process of the cornea being under pressure during the process of the indenter pressing towards the cornea. The recovery subsequence is a sequence composed of the frame images corresponding to the process of the cornea rebounding due to the gradually decreasing pressure during the recovery process after the indenter presses.

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

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

[0096] In this step, existing image recognition methods can be used to determine the corneal contour of each frame image in the image sequence.

[0097] Because during the video data acquisition process, the position, parameters, etc. of the high-precision camera and the cornea do not change. Therefore, the overall position of the cornea in each frame image is stationary, and only the compressed and deformed contour will change, as Figure 5 shows a schematic diagram of the change in the corneal contour under pressure, where (a) is the corneal contour without pressure, (b) is the corneal contour when under pressure but not at the maximum indentation, and (c) is the corneal contour at the maximum indentation.

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

[0099] Since the overall position of the cornea in each frame image is stationary, the center point of the corneal contour can be recognized in the first frame image of the image sequence, as Figure 5Point A in (a), determine the coordinates of point A in the pixel coordinate system (as shown in the figure, 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 rightward direction 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 process of corneal compression, the ordinate value of point A in the pixel coordinate system remains unchanged, while the abscissa value changes. Therefore, based on the ordinate value of point A, in other frames of the image, determine the point on the corneal contour corresponding to this ordinate value. This point is the center point of this frame of the image, and its coordinates are the center point coordinates.

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

[0101] Since the ordinate of the center point of each frame does not change, therefore, the coordinate difference is actually the abscissa difference, that is, the distance by which the center point is indented.

[0102] 4. When there first appears a frame of the image whose center point coordinate difference is greater than the preset coordinate difference threshold, and the center point coordinate differences of the subsequent consecutive first preset number of frames of the image are all greater than the preset coordinate difference threshold, then is used as the first frame of the compressed subsequence.

[0103] For example, if the first preset number is 5, then it means the center point coordinate differences of the subsequent consecutive 4 frames of the image are all greater than the preset coordinate difference threshold. The preset coordinate difference threshold is 0, or 3, etc.

[0104] Taking the preset coordinate difference threshold = 0 and the first preset number = 5 as an example, since the video data is collected during the process of the indenter 19 indenting the cornea, and the process of the indenter 19 indenting the cornea cannot ensure that the first frame of the video data is the start of the pressing. For example, the pressure is applied 2 seconds after the start of the pressing. Then, the center point of the corneal contour in the video data 2 seconds ago does not change, while the compressed subsequence should start from the first frame of the applied pressure. Therefore, the center point coordinate differences of adjacent two frames will be compared.

[0105] For example, starting from the first frame of the image sequence, the center point coordinate difference between the second frame and the first frame is 0, the center point coordinate difference between the third frame and the second frame is 0, which indicates that the cornea has not been pressured at this time. The center point coordinate difference between the fourth frame and the third frame is 0,..., until the frame and the frame has a center point coordinate difference of 3, then it is very likely that the cornea is pressured at this time.

[0106] In actual application, it is possible that due to inevitable jitter, the center point coordinate difference is non-zero. Therefore, after the frame and the The coordinate difference of the center point of the frame is non-zero. The frame and the frame have a non-zero coordinate difference of the center point, … If within the next five consecutive frames are all non-zero, it indicates that the error is not caused by accidental jitter. At this time, can be determined as the first frame image of the compressed subsequence.

[0107] 5. When after that, for the first time, a frame image whose coordinate difference of the center point is not greater than the preset coordinate difference threshold, and for the next second preset number of consecutive frame images, the coordinate differences of the center points are all not greater than the preset coordinate difference threshold, then is determined as the last frame image of the compressed subsequence.

[0108] When the cornea reaches the maximum indentation, it will maintain a certain contour. That is to say, for the first time, a frame image whose coordinate difference of the center point is not greater than the preset coordinate difference threshold, and for the next second preset number of consecutive frame images, the coordinate differences of the center points are all not greater than the preset coordinate difference threshold, then it is considered that the cornea reaches the maximum indentation at this time, that is, the compression process is completed. Then is determined as the last frame image of the compressed subsequence.

[0109] Taking the preset coordinate difference threshold = 0 and the second preset number = 3 as an example, after the coordinate difference of the center point between the frame and the frame is non-zero, but the coordinate difference of the center point between the frame and the frame is zero, the coordinate difference of the center point between the frame and the frame is zero, the coordinate difference of the center point between the frame and the frame is zero. Then is considered as the last frame image of the compressed subsequence.

[0110] From to the frame images form a compressed subsequence, where the compressed subsequence contains and

[0111] 6. When after that, for the first time, a frame image whose coordinate difference of the center point is greater than the preset coordinate difference threshold, and for the next third preset number of consecutive frame images, the coordinate differences of the center points are all greater than the preset coordinate difference threshold, then is determined as the first frame image of the recovery subsequence.

[0112] 7. When after that, for the first time a frame of image appears whose central point coordinate difference is not greater than a preset coordinate difference threshold, and the central point coordinate differences of the next consecutive fourth preset number of frames of images are all not greater than the preset coordinate difference threshold, then is used as the last frame of the recovery subsequence.

[0113] By the same token, in after that, if the central point coordinate difference is greater than the preset coordinate difference threshold again, the recovery process is entered, and when the central point coordinate differences are all not greater than the preset coordinate difference threshold again, the recovery process is completed. This process is the reverse process of the compression process. For the extraction process of the compression subsequence in the above compression process, no detailed explanation will be given here.

[0114] In addition, since there is no restriction on the acquisition angle of the high-precision camera, it is possible that due to occlusion, the standard corneal contour image reaching the maximum indentation may not be acquired, such as being occluded by the corneal contour edge. For example, the entire pressing process is 7 seconds, where 1 second to 3 seconds is the compression process, 4 seconds reaches the maximum indentation, and 5 seconds to 7 seconds is the recovery process. However, in the video data, starting from the data at the 2nd second, the corneal contour does not change anymore (because it is occluded by the corneal edge and the central point cannot be seen in the image, so the position of the central point does not change) until it starts to change again at the 6th second. At this time, the compression subsequence is the sequence composed of the image data at the 1st and 2nd seconds, and the recovery subsequence is the sequence composed of the image data at the 6th and 7th seconds. Then the sequence composed of the image data between 3 seconds and 5 seconds is the adjustment subsequence. In the adjustment subsequence, although the corneal contour does not change, the actual cornea has experienced a process of partial compression - reaching the maximum indentation - partial recovery.

[0115] 102 - 3. Obtain the compression parameters based on the compression subsequence and obtain the recovery parameters based on the recovery subsequence.

[0116] Among them, both the compression parameters and the recovery parameters include duration, corneal displacement difference sequence, and maximum displacement difference. That is to say, the parameter items included in the compression parameters and the recovery parameters are the same, but the values of each parameter item are different.

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

[0118] 211. Determine the acquisition time of the first frame of the compression subsequence and the acquisition time of the last frame of the compression subsequence

[0119] where I is the total number of images in the compression subsequence.

[0120] 212. Determine the position of the cornea in each frame image of the compressed 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 abscissa of the center point of the central area of the cornea in each frame image

[0122] 213. Determine the position difference between two adjacent frame images of the compressed subsequence

[0123] It can be the difference in the abscissa of the center point of the central area between two adjacent frame images, and this value is actually the distance by which the center point of the central area is indented due to the pressure of the indenter

[0124] 214. Determine the duration in the compression parameters The corneal displacement difference sequence is The maximum displacement difference

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

[0126] 221. Determine the acquisition time of the first frame image of the recovery subsequence and the acquisition time of the last frame image

[0127] where J is the total number of images in the recovery subsequence

[0128] 222. Determine the position of the cornea in each frame image of the recovery subsequence

[0129] where j is the image identifier in the recovery subsequence It can be the coordinates of the center point of the central area of the cornea in each frame image, or the abscissa of the center point of the central area of the cornea in each frame image

[0130] 223. Determine the position difference between two adjacent frame images of the recovery subsequence

[0131] It can be the difference in the abscissa of the center point of the central area between two adjacent frame images, and this value is actually the distance by which the center point of the central area is restored due to the gradually decreasing pressure of the indenter

[0132] 224. Determine the duration in the recovery parameters The corneal displacement difference sequence is The maximum displacement difference

[0133] 102 - 4. Determine the adjustment value according to the compression parameter and the recovery parameter.

[0134] The implementation process of this step is as follows:

[0135] 1. In the image sequence, form an adjustment subsequence from the consecutive frame images between the (x + 1)-th frame image and the (x - 1)-th frame image. d + 1 frame image to the x u - 1 frame image.

[0136] Among them, x d is the serial number of the last frame image in the compression subsequence in the image sequence, and x u is the serial number of the first frame image in the recovery subsequence in the image sequence.

[0137] Since there is no restriction on the acquisition angle of the high-precision camera, it is possible that due to occlusion, the standard corneal contour image reaching the maximum indentation may not be acquired. For example, during the entire pressing process of 7 seconds, the 1st to 3rd seconds are the compression process, the 4th second reaches the maximum indentation, and the 5th to 7th seconds are the recovery process. However, in the video data, starting from the data of the 2nd second, the corneal contour does not change anymore (because it is blocked by the corneal edge and the center point cannot be seen in the image, so the position of the center point no longer changes) until the 6th second when it starts to change again. At this time, the compression subsequence is the sequence composed of the image data of the 1st and 2nd seconds, and the recovery subsequence is the sequence composed of the image data of the 6th and 7th seconds. Then the sequence composed of the image data between the 3rd and 5th seconds is the adjustment subsequence. In the adjustment subsequence, although the corneal contour does not change, the actual cornea has experienced a process of partial compression - reaching the maximum indentation - partial recovery.

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

[0139] Among them, K is the total number of images in the adjustment subsequence.

[0140] 3. Determine the standard value S of the compression process according to the compression parameter d , and determine the standard value S of the recovery process according to the recovery parameter 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 duration when the cornea stops deforming when it reaches the maximum indentation (this value can be comprehensively set according to the pressure application situation and the average cornea stop deformation time, and the average cornea stop deformation time can be obtained in advance by testing a large number of corneas).

[0144] Next, taking S d as an example, the characterization of each parameter will be described. The parameter characterization of S u can be referred to S d and will not be described herein.

[0145] Characterizes the moving speed of the center point of the compression process from the perspective that can be monitored from the video data, and this speed is used as the possible maximum moving speed during the cornea compression process. Characterizes the average moving distance between two adjacent frames, Characterizes the moving speed of the center point of the compression process from the perspective of frames, and this speed is used as the most likely moving speed during the cornea compression process. Characterizes the minimum moving speed of the center point of the compression process from the perspective of frames, and this speed is used as the possible minimum moving speed during the cornea compression process. Characterizes the average speed during the entire cornea compression process. Δt d Characterizes the total duration of the compression process from the perspective that can be monitored from the video data. Since there may be a process that is not monitored by the video data, that is Characterizes the total duration of the unmonitored compression process. Then characterizes the total duration of the entire compression process. S d Then characterizes the displacement of the cornea during the entire compression process.

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

[0147] 4. Determine the maximum displacement S of the cornea according to the measurement data 0 .

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

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

[0150] S 0 is the displacement of the cornea measured according to the measurement data, and S d , S u are the displacements 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: Determine the first difference β1 = |S d - S u |, the second difference β2 = |S 0 - S u |, and the third difference β3 = |S 0 - S d |. Determine the average difference and the standard deviation The determined adjustment value is

[0152] The first difference, the second difference, and the third difference characterize the differences between the three corneal displacements, which characterizes the degree of variation between these three differences.

[0153] If this degree of variation is small, it indicates that this 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 this degree of variation is large, it indicates that there may be inaccurate situations in the test data.

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

[0155] The implementation process of step 103 is as follows:

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

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

[0158] Among them, the adjustment maximum is

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

[0160] is the degree of variation obtained during the compression process, is the degree of variation obtained during the recovery process, and AD 0 is the degree of variation 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 indicates 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. Therefore, it is determined that the measurement data meets the measurement accuracy condition. Otherwise, it indicates that the test data may be inaccurate, and the execution of the corneal biomechanical property measurement method provided in this embodiment can be terminated for early warning so as to perform measurement again.

[0163] 104. If the measurement accuracy condition is met, the corneal biomechanical properties are measured based on the pressure data and the measurement data.

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

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

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

[0167] For example, the curvature information is determined by analyzing the distribution image of the light spot on the cornea. The corneal curvature is calculated by using the spherical mirror imaging method. The cornea can be approximated as a spherical mirror with a curvature radius of r and a focal length of f. The image h' of the LED light spot h formed after reflection by the cornea, 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. From the imaging formula, we can get:

[0168] Under normal circumstances, for a spherical mirror Since the curvature radius of the cornea is much smaller than the working distance, CFD = d. Therefore, the corneal curvature radius

[0169] The structure of the cornea and the displacement of the cornea can be obtained according to the interfered signal and the two-dimensional or three-dimensional structure image of the cornea.

[0170] The position information of the anterior surface, posterior surface of the cornea and the anterior surface of the lens can be determined through the OCT map of the longitudinal structure of the cornea.

[0171] The thickness TH of the cornea can be obtained from the longitudinal structure information acquired by measuring the cornea using OCT. The thickness TH is the distance difference between the anterior surface and the posterior surface of the cornea. The deformation of the cornea is calculated from the displacement of the cornea relative to the anterior surface of the lens during the indentation measurement, or the indentation distance can also be calculated.

[0172] Based on the Imbert - Fick principle, when the indenter contacts and indents the cornea, the calculation formula for the elastic modulus (Young's modulus) of the cornea can be derived according to the mechanical equilibrium model:

[0173]

[0174] where 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 exerted on the cornea, δ is the displacement of the corneal indentation, represents the slope of the pressure - displacement curve, and a is the corneal geometric constant factor.

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

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

[0177] where r0 is the contact area between the indenter and the cornea.

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

[0179] The method for measuring the biomechanical properties of the cornea provided in this embodiment collects pressure data, measurement data, and video data during the process of the cornea being compressed; 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 it meets the measurement accuracy condition, then measures the biomechanical properties of the cornea based on the pressure data and the measurement data. The method of this embodiment can judge the accuracy of the measurement data through the adjustment value determined according to the video data. Only after the accuracy meets the measurement accuracy condition, the biomechanical properties of the cornea are measured based on the pressure data and the measurement data, achieving accurate measurement of the biomechanical properties of the cornea.

[0180] It should be clear that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are 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 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 executed in the order mentioned in the embodiments, or different from the order in the embodiments, or several steps can be executed 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate 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 includes: Collecting pressure data, measurement data, and video data during the process of corneal compression; 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 corneal biomechanical properties according to the pressure data and the measurement data; The measurement data includes: the distribution image of the light spot on the cornea, the two-dimensional or three-dimensional structure image of the cornea obtained by the OCT measurement device, and the OCT information obtained by the differential detection device; Wherein, the determining the adjustment value according to the video data includes: Splitting the video data into multiple frames of images, sorting the multiple frames of images in order from far to near in terms of acquisition time to obtain an image sequence; Extracting a compression subsequence and a recovery subsequence from the image sequence; Obtaining a compression parameter based on the compression subsequence and obtaining a recovery parameter based on the recovery subsequence; Determining the adjustment value according to the compression parameter and the recovery parameter.

2. The method according to claim 1, wherein The extracting the compression subsequence and the recovery subsequence from the image sequence includes: Determining the corneal contour of each frame of image in the image sequence; Determining the coordinates of the central point in the central area of the cornea in each frame of image according to the corneal contour; Starting from the first frame of the image sequence, comparing the difference in the coordinates of the central point between it and the subsequent frame of image; When a frame of image first appears the coordinate difference of its center point is greater than a preset coordinate difference threshold, and the coordinate differences of the center points of the subsequent first preset number of frames of images are all greater than the preset coordinate difference threshold, then is used as the first frame of image of the compression subsequence; When after that, when a frame of image first appears the difference in the central point coordinates of which is not greater than a preset coordinate difference threshold, and the differences in the central point coordinates of the subsequent second preset number of consecutive frames of images are not greater than the preset coordinate difference threshold, then it is used as the last frame of the compressed subsequence; When after that, when a frame of image first appears whose central point coordinate difference is greater than a preset coordinate difference threshold, and the central point coordinate differences of the next consecutive third preset number of frames of images are all greater than the preset coordinate difference threshold, then is used as the first frame of image of the recovery subsequence; When after that, when a frame of image first appears whose central point coordinate difference is not greater than a preset coordinate difference threshold, and the central point coordinate differences of the next consecutive fourth preset number of frames of images are not greater than the preset coordinate difference threshold, then it is used as the last frame of the restored subsequence.

3. The method according to claim 1, wherein Both the compression parameter and the recovery parameter include duration, corneal displacement difference sequence, and maximum displacement difference; The obtaining the compression parameter based on the compression subsequence includes: Determine the acquisition time of the first frame image of the compressed subsequence and the acquisition time of the last frame 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 positional difference between two adjacent frames of the compressed subsequence Determine the duration in the compression parameters The corneal displacement difference sequence is The maximum displacement difference The obtaining 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 image where J is the total number of images in the recovery subsequence; Determine the position of the cornea in each frame image of the restored subsequence where j is the image identifier in the restored subsequence; Determine the positional difference between two adjacent frames of the recovery subsequence Determine the duration in the recovery parameters The corneal displacement difference sequence is The maximum displacement difference 4. The method according to claim 3, wherein The determining the adjustment value according to the compression parameter and the recovery parameter includes: In the image sequence, consecutive frame images between the (x + 1)-th frame image and the (x - 1)-th frame image form an adjustment subsequence; where x d is the sequence number of the last frame image in the compression subsequence in the image sequence, and x u is the sequence number of the first frame image in the recovery subsequence in the image sequence; d is the sequence number of the last frame image in the compression subsequence in the image sequence, and x u is the sequence number of the first frame image in the recovery 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 image where K is the total number of images in the adjustment subsequence; Determine the standard value S of the compression process according to the compression parameter d , determine the standard value S of the recovery process according to the recovery parameter u ; Determine the maximum displacement S of the cornea based on the measurement data 0 ; Determine the adjustment value according to S 0 and S d and S u ​ 5. The method according to claim 4, characterized in that Wherein, α is the acquisition time difference between two adjacent frames in the image sequence, and θ is the duration when the cornea stops deforming when reaching the maximum indentation.

6. The method according to claim 4, wherein The adjustment value determined according to S 0 , S d , S u includes: Determine the first difference β1 = |S d - S u |, the second difference β2 = |S 0 - S u |, and the third difference β3 = |S 0 - S d |; Determine the average difference and the standard deviation Determine that the adjustment value is 7. The method according to claim 3, wherein The determining whether the measurement data meets the measurement accuracy condition according to the adjustment value includes: Determine CD d the mean μ of all elements in d and the standard deviation σ d ; determine CD u the mean μ of all elements in u and the standard deviation σ u ; According to μ d , σ d , μ u , σ u Determine the adjusted maximum value; If the adjustment value is not greater than the maximum adjustment value, determining that the measurement data meets the measurement accuracy condition.

8. The method according to claim 7, wherein Said according to μ d 、σ d 、μ u 、σ u Determine the adjustment maximum value, including: Determine that the adjustment maximum value is Among them, AD 0 is a preset precision threshold.

9. The method according to claim 1, characterized in that Collecting the pressure data and the measurement data during the process of corneal compression includes: During the process of controlling the indenter to press against the cornea and emitting ultrasonic waves to the cornea, the pressure data received by the cornea is measured in real time by a mechanical sensor, and the echo data reflected by the cornea is received.

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