Postoperative corneal stress change detection system for refractive surgery and working method of postoperative corneal stress change detection system

Abstract

The invention provides a cornea stress change detection system after a refractive operation and a working method thereof, and the cornea stress change detection system can noninvasively evaluate the biomechanical property of a cornea and is particularly suitable for the field of refractive operations. By measuring SSI and other key parameters, the system is helpful for doctors to make more accurate treatment decisions and optimize surgical selection and surgical design. More accurate and quantitative corneal biomechanical parameters, such as SSI, can be provided to assess the surgical effect. And biomechanical changes and complication risks possibly occurring after an operation can be found in an early stage. And the influence of different operation modes on cornea biomechanics can be better compared.

Description

Technical Field

[0001] The present application belongs to the field of refractive correction technology, and in particular to a system for detecting corneal stress changes after refractive surgery and a working method thereof. Background Art

[0002] With the continuous development of corneal refractive surgery technology, corneal biomechanical properties as an important observation index for the safety, effectiveness, stability and predictability of corneal refractive surgery have received more and more attention. Corneal refractive surgery changes the refractive state of the cornea by cutting the cornea, thereby achieving the purpose of correcting refractive errors. The changes in corneal thickness, corneal morphology, and the destruction and reconstruction of corneal collagen fibers change the biomechanical properties of the cornea. The mechanical stability of the cornea not only helps maintain the normal morphology of the cornea, but also affects whether the ideal refractive state and visual quality can be achieved after corneal refractive surgery. On the contrary, changes in corneal mechanical stability and abnormal healing can lead to serious postoperative complications, such as keratoconus, especially in people who are susceptible to corneal ectatic diseases. The effect of corneal refractive surgery on corneal biomechanical stability is related to the safety, effectiveness, predictability and long-term stability of the surgery, and there is a risk of triggering serious postoperative complications. Different surgical methods and different surgical parameter designs have different effects on corneal biomechanics. Therefore, the evaluation of corneal biomechanics before and after corneal refractive surgery is very important, and the application of corneal biomechanical measurement in the field of refractive surgery has received widespread attention and has developed rapidly. Comparing the differences between different surgeries from a biomechanical perspective, standardizing and quantifying the measurement of corneal biomechanics before and after refractive surgery is conducive to improving the predictability of the postoperative effects of corneal refractive surgery and helping to optimize the personalized selection of corneal refractive surgery and the personalized design of surgical parameters from a biomechanical perspective.

[0003] Corneal tissue is a biological tissue structure with complex material properties. The biomaterial properties of the cornea make the cornea have complex mechanical properties such as non-uniformity, nonlinearity, viscoelasticity, anisotropy, etc. The biomechanical properties of the cornea are not an independent corneal material property, it is closely related to many factors, which makes it very difficult to independently evaluate the in vivo corneal biomechanics clinically. The various indicators used to evaluate corneal biomechanics clinically are inevitably affected by multiple factors such as intraocular pressure, corneal thickness, eye axis, corneal morphology, curvature, etc. Summary of the invention

[0004] The present invention aims at the technical problems raised by the background technology and proposes a corneal stress change detection system after refractive surgery and a working method thereof.

[0005] In a first aspect, the present invention discloses a system for detecting corneal stress changes after refractive surgery, the system comprising:

[0006] a. Data input module, used to receive the patient's basic information and corneal biomechanical parameters before and after surgery;

[0007] b. Data processing module, used to analyze the input corneal biomechanical parameters and calculate the corneal stress strain index (SSI);

[0008] c. Data storage module, used to store basic patient information, pre- and post-operative corneal biomechanical parameters, and calculated SSI;

[0009] d. Result output module, used to display the detection results of corneal stress changes.

[0010] Preferably, the data processing module includes:

[0011] a. Finite element (FE) numerical model to simulate the effects of intraocular pressure and Corvis-ST air jet on the cornea;

[0012] b. Numerical estimation unit, used to perform numerical estimation based on the prediction results of the FE model by the least square method;

[0013] c. Algorithm validation unit, used to evaluate the correlation of the algorithm with intraocular pressure, central corneal thickness (CCT) and age through a clinical database.

[0014] Preferably, the data input module further comprises:

[0015] a. Patient basic information input interface, including but not limited to the patient's age, gender and surgical method;

[0016] b. Biomechanical parameter input interface, used to input preoperative and postoperative corneal biomechanical parameters.

[0017] Preferably, the data storage module adopts a database management system for organizing and indexing stored data.

[0018] Preferably, the result output module includes:

[0019] a. Graphical user interface (GUI) for displaying visualization results of corneal stress changes;

[0020] b. Report generator, used to generate detailed reports containing test results.

[0021] In a second aspect, the present invention further discloses a working method of a system for detecting corneal stress changes after refractive surgery, comprising the following steps:

[0022] a. Receive the patient's basic information and pre- and post-operative corneal biomechanical parameters through the data input module;

[0023] b. Analyze the input corneal biomechanical parameters and calculate SSI using the data processing module;

[0024] c. storing the patient's basic information, preoperative and postoperative corneal biomechanical parameters and the calculated SSI in the data storage module;

[0025] d. Display the detection results of corneal stress changes through the result output module.

[0026] Furthermore, in step b, the analysis process of the data processing module includes:

[0027] a. Use FE numerical model to simulate the effect of intraocular pressure and Corvis-ST jet on cornea;

[0028] b. Perform numerical estimation based on the prediction results of the FE model using the numerical estimation unit;

[0029] c. The correlation between the algorithm and intraocular pressure, CCT and age was evaluated through the algorithm verification unit.

[0030] Furthermore, in step b, the calculation steps of SSI are:

[0031] The finite element FE numerical model simulates intraocular pressure and Corvis-ST jet. Based on the prediction of the corneal deformation response of Corvis-ST, the central corneal thickness CCT, biomechanically corrected intraocular pressure BIOP and the corneal hardness parameter SP-HC at maximum concave are used as input and output parameters for numerical simulation. The least squares method is used for numerical estimation, and then the algorithm is verified by the correlation between the algorithm evaluated by two large clinical databases and intraocular pressure, CCT and age. Finally, an index SSI reflecting the hardness of the corneal material is obtained.

[0032] Furthermore, in step b, the calculation steps of SSI are:

[0033] The Corvis-ST aimed air pulse can generate a constant maximum pump pressure, ensuring that the dynamic deformation response of the cornea is comparable between different individuals;

[0034] The Scheimpflug ultra-high-speed imaging system can capture 4430 frames of images per second. Within 31ms of the air pulse being activated, the high-speed camera can capture 140 frames of horizontal cross-sectional images of the cornea, and can fully and clearly describe the entire process of the dynamic deformation response of the cornea, including the cornea's initial convex state to the air pulse flattening the cornea into the concave phase and reaching the maximum depression state, and finally returning to the original shape. Corvis-ST measures the values ​​of the pre-deformation phase, inward movement convex phase, inward movement concave phase, oscillation phase, outward movement concave phase, outward movement convex phase, and posterior corneal flexion phase of the dynamic deformation response of the cornea.

[0035] In a third aspect, the present invention discloses a computer-readable storage medium, on which a computer program is stored, and the program is configured to execute the steps of the method described in the second aspect.

[0036] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0037] 1) Able to provide quantitative corneal biomechanical parameters, such as SSI, to evaluate surgical outcomes.

[0038] 2) It helps to detect the biomechanical changes and complication risks that may occur after surgery at an early stage.

[0039] 3) It helps to compare the effects of different surgical methods on corneal biomechanics. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 is a schematic diagram of corneal stress strain index provided in an embodiment of the present application;

[0042] Figure 2 It is a diagram of various stages of corneal deformation response to Corvis-ST jet provided in the embodiment of the present application;

[0043] Figure 3 This is the Corvis-ST parameter display interface provided in the embodiment of the present application. Figure 1 ;

[0044] Figure 4 This is the Corvis-ST parameter display interface provided in the embodiment of the present application. Figure 2 ;

[0045] Figure 5 The preoperative SSI and IOP provided in the embodiment of this application are NCT Correlation scatter plot of ;

[0046] Figure 6 This is a scatter plot of the correlation between preoperative SSI and IOP provided in the embodiment of the present application

[0047] Figure 7 is a scatter plot of the correlation between preoperative SSI and BIOP provided in an embodiment of the present application;

[0048] Figure 8Graph showing changes in various Corvis-ST parameters before and after surgery provided in the embodiments of the present application. DETAILED DESCRIPTION

[0049] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0050] Example

[0051] Materials and Methods

[0052] 1. Research subjects

[0053] A total of 114 myopic patients who underwent refractive surgery in the Eye Refractive Center of the Affiliated Hospital of Yunnan University were selected, and one eye was randomly selected as the research object, a total of 114 eyes. According to the surgical method, they were divided into two groups, including 74 cases in the SMILE group and 40 cases in the FS-LASIK group; 47 males and 67 females; the average age was (24.54±5.10) years old; the average preoperative spherical equivalent power was (-5.38±1.90)D; the average central corneal thickness was (539.20±26.59)μm. Inclusion criteria: age 18-45 years old; central corneal thickness greater than 480nm; refractive error change less than 0.5D in the past two years; soft contact lens wearers stopped wearing for at least 1 week, hard contact lens wearers stopped wearing for at least 3 weeks, and orthokeratology lens wearers needed to stop wearing for more than 3 months. Exclusion criteria: history of previous ophthalmic surgery, other eye diseases such as keratoconus, glaucoma, cataract, corneal scar, corneal dystrophy, severe dry eyes, etc.; corrected visual acuity below 0.8; diabetes, hypertension, systemic immune system abnormalities, etc.; pregnancy, breastfeeding and preparation for pregnancy; other contraindications to refractive surgery.

[0054] This example complies with the requirements of the Declaration of Helsinki and was approved by the Medical Ethics Committee of the Affiliated Hospital of Yunnan University (approval number: 202134), and all patients gave informed consent.

[0055] 2. Surgical methods and postoperative treatment

[0056] Gatifloxacin eye gel was applied at least 12 times 1-3 days before the operation. Oxybuprocaine hydrochloride eye drops were used for surface anesthesia before the operation. Routine disinfection, draping, conjunctival sac flushing, and eyelid opening device were performed.

[0057] Patients in the SMILE group underwent corneal lens cutting and lateral incision making using the Visumax femtosecond laser system (Zeiss, Germany). The parameter design was as follows: laser energy 160 nj, point spacing 4.5 μm, corneal cap thickness 110-130 μm, lens diameter 6.8-7.5 mm, optical zone diameter 6.0-6.7 mm, lateral incision 2 mm, located in the 90° direction, and lateral cutting angle of 110°.

[0058] The patients in the FS-LASIK group used the Visumax femtosecond laser system to make a corneal flap. The parameters were as follows: laser energy 170nj, point spacing 4.5μm, corneal flap diameter 8.0mm, corneal flap thickness 100-110μm, optical zone diameter 6.0-6.5mm, pedicle located at the top, and a micro corneal spatula was used to open the corneal flap after making the corneal flap. After opening the flap, the Allegretto wava / eyeQ (Wavelihgt, Germany) laser system was used to complete the precise ablation of the corneal stroma under the corneal flap. The surgical operations were all performed by the same skilled doctor. The operation went smoothly and no adverse events were found during the operation.

[0059] Loteprednol eye drops were used 4 times a day for 2 weeks after surgery; gatifloxacin eye gel was used 4 times a day for 2 weeks; recombinant epidermal growth factor eye drops were used 4 times a day for 2 weeks; calf blood deproteinized eye gel was used once a night for 1 month; sodium hyaluronate eye drops were used 4 times a day from 1 week after surgery to 3 months after surgery. No infection, corneal ectasia, corneal cap and corneal flap related complications, trauma and other adverse conditions occurred during the postoperative follow-up.

[0060] 3. Corneal biomechanical measurement methods

[0061] The Corvis-ST corneal biomechanical measuring instrument obtains the corneal biomechanical parameters of the patient. Corvis-ST is an instrument commonly used in clinical practice to measure the biomechanical properties of the cornea in vivo. It measures the biomechanical properties of the cornea by describing the dynamic deformation response of the cornea under air pulses. Its Scheimpflug ultra-high-speed imaging system can capture 4430 frames of images per second. Within 31ms of the start of the air pulse, the high-speed camera can complete the capture of 140 frames of horizontal cross-sectional images of the cornea, which can completely and clearly describe the entire process of the dynamic deformation response of the cornea. Corvis-ST measures the pre-deformation phase, inward movement convex phase, inward movement concave phase, oscillation phase, outward movement concave phase, outward movement convex phase, and posterior corneal flexion phase of the dynamic deformation response of the cornea ( Figure 2 ), and obtain a series of corneal dynamic response parameters to reflect the biomechanical characteristics of the cornea.

[0062] All patients underwent Corvis-ST examinations at three follow-up visits before surgery, 1 month after surgery, and 3 months after surgery. The measurement quality QS (quality standard) was OK. If QS was model deviation (MD), the measurement was repeated three times and the average value was taken. All data were collected completely and the repeatability was good. Obtain and record relevant parameters ( Figure 3 ), including corneal stress strain index (SSI), intraocular pressure (IOP), biomechanically corrected intraocular pressure (BIOP), the first applanation time / length / rate (the first applanation time, A1T; the first applanation length, A1L; the first applanation velocity, A1V), the second applanation time / length / rate (the second applanation time, A2T; the second applanation length, A2L; the second d applanation velocity, A2V), peak distance (Peak distance, PD), deformation amplitude (Deformation Amplitude, DA), deformation amplitude ratio (Deformation Amplitude Ratio, DARatio), radius of corneal curvature at highest concavity (Radius of corneal curvature at highest concavity, HC Radius), time from the measurement beginning to the moment of reaching the highest concavity, HCT, integrated radius (Integrated Radius, IRA), Ambrosio related thickness-horizontal direction (Ambrosio Relational Thicknes in the horizontal (ARTh), corneal hardness parameters at the first press (SP-A1). All examinations were performed by the same experienced professional physician.

[0063] Acquisition of SSI data

[0064] Corneal tissue is a biological tissue structure with complex material properties. The biomaterial properties of the cornea make the cornea have complex mechanical properties such as non-uniformity, nonlinearity, viscoelasticity, anisotropy, etc. The corneal biomechanical properties are not independent corneal material properties, but are closely related to many factors. This makes it very difficult to independently evaluate the corneal biomechanics in vivo clinically. The various indicators used to evaluate corneal biomechanics in clinical practice are inevitably affected by multiple factors such as intraocular pressure, corneal thickness, eye axis, corneal morphology, curvature, etc.

[0065] Finite element (FE) numerical model was used to simulate intraocular pressure and Corvis-ST air jet. Based on the prediction of the corneal deformation response of Corvis-ST, central corneal thickness (CCT), biomechanically-corrected IOP (BIOP) and corneal hardness parameters at the highest concavity (SP-HC) were used as input and output parameters for numerical simulation. The least squares method was used for numerical estimation. Then, the algorithm was verified by evaluating its correlation with intraocular pressure, CCT and age using two large clinical databases. Finally, an index reflecting the hardness of corneal material, SSI, was obtained.

[0066] SSI describes the strain effect of the cornea under different stresses. It is believed to eliminate the influence of corneal thickness and intraocular pressure on biomechanics, and can independently reflect corneal hardness, making it possible to clinically measure the hardness of corneal biomaterials in vivo, non-invasively, and reliably. In the field of refractive surgery, preoperative corneal ectasia risk assessment, selection of surgical methods and surgical parameter design, and early diagnosis of postoperative corneal ectasia diseases are all inseparable from the measurement of corneal biomechanical properties. A reliable corneal biomechanical index is particularly important when corneal thickness, morphology, curvature, etc. change significantly after corneal refractive surgery.

[0067] This example confirms that SSI is unrelated to CCT and weakly correlated with intraocular pressure. SSI has certain advantages over other biomechanical indicators in independently reflecting corneal hardness. SMILE surgery is superior to FS-LASIK surgery in postoperative corneal biomechanical stability, but in terms of corneal material hardness reflected by SSI, there is no significant difference between the two surgical methods. Therefore, SSI has important clinical application value in the field of corneal refractive surgery. It is expected to be unaffected by corneal cutting in corneal refractive surgery and reflect the true corneal material stiffness.

[0068] Get more accurate data from SSI

[0069] Corvis-ST is an instrument commonly used in clinical practice to measure corneal biomechanical properties in vivo. It measures the biomechanical properties of the cornea by describing the dynamic deformation response of the cornea under air pulses. The Corvis-ST aimed air pulse can generate a constant maximum pressure pump to ensure the comparability of the dynamic deformation response of the cornea in different individuals; the Scheimpflug ultra-high-speed imaging system can capture 4430 frames of images per second. Within 31ms of the start of the air pulse, the high-speed camera can complete the capture of 140 frames of corneal horizontal cross-sectional images, which can completely and clearly describe the entire process of the corneal dynamic deformation response, including the cornea from the initial convex state to the air pulse flattening the cornea into the concave phase and reaching the maximum depression state, and finally returning to the original shape. Corvis-ST measures the corneal dynamic deformation response in each stage of the deformation pre-phase, inward movement convex phase, inward movement concave phase, oscillation phase, outward movement concave phase, outward movement convex phase, and posterior corneal flexion phase ( Figure 2 ), a series of corneal dynamic response parameters including SSI are obtained to reflect the biomechanical characteristics of the cornea. In the actual clinical application process, it is very important to obtain accurate and effective SSI parameters. In the process of corneal biomechanics (SSI) measurement, the cooperation of the patient, the operation of the technician and the judgment of the technician on the validity of the results are indispensable. When collecting data, the patient's head and eye position must be correct, the patient's forehead must be close to the forehead support, and the lower jaw must be fixed. The subject is asked to blink and open his eyes to look at the central fixation light, avoid blinking or turning the eyeballs, and use the Corvis ST (Oculus, Germany) instrument pressure head to automatically identify the corneal vertex and apply air pulse pressure airflow to the cornea. The measurement quality QS (quality standard) is OK. If QS is model deviation (MD), the measurement is repeated three times and the average value is taken. The data collection is complete and the repeatability is good. Good measurement results can ensure that the SSI value truly reflects the hardness of the corneal material.

[0070] All patients received routine preoperative examinations for corneal refractive surgery. Information such as intraocular pressure (NCT), corneal thickness, refraction, and spherical equivalent (SE) were obtained through non-contact intraocular pressure (NIDEK NT-510), pantacam corneal topography (OCYLUS), contact A-ultrasound central corneal thickness (TOMEY SP-100), and non-ciliary muscle paralysis subjective optometry (NIDEKAOS-3000). The visual acuity, intraocular pressure, refractive status, and corneal healing were followed up 1 day, 1 week, 1 month, and 3 months after surgery. No postoperative complications were found.

[0071] 5. Statistical methods

[0072] SPSS23.0 statistical software was used to analyze the data. Normally distributed quantitative data were expressed as (mean±SD), and skewed quantitative data were expressed as M(IQR); two independent sample t-tests were used to compare the biomechanical parameters between the two surgical methods at different time points for data that were normally distributed, and repeated measures analysis of variance was used to compare the biomechanical changes before and after surgery within the group; the rank sum test was used to compare the quantitative data between the groups for non-normal distribution, and the Friedman test was used for intra-group comparison; simple effect or Fisher's least significant difference (LSD) test was used to compare the biomechanical indicators with significant differences within the group at three time points before surgery, 1 month after surgery, and 3 months after surgery. P<0.05 indicated that the difference was statistically significant.

[0073] result

[0074] 1. Preoperative baseline data

[0075] A total of 114 patients were included, and their baseline data are shown in Table 1 .

[0076] Two independent sample t-tests were used to analyze and compare the baseline data of the two groups of patients.

[0077] As shown in Table 2, the preoperative age and intraocular pressure (IOP) of the two groups of patients NCT There were no significant differences in the main corneal biomechanical parameters between the two groups before surgery. The data with normal distribution were compared with two independent sample t-tests, and the data with non-normal distribution were compared with rank sum tests.

[0078] As shown in Table 3, there were no significant differences in SSI, A1T, A1L, A1V, A2T, A2L, A2V, PD, DA, DA Ratio, HCRadius, HCT, IRA, ARTh, and SP-A1 between the two groups before surgery (P>0.05). Although there was a difference in the preoperative spherical equivalent between the two surgical methods (P<0.01),

[0079] However, we believe that since different surgical methods require different amounts of corneal tissue to be cut and the thickness of the corneal cap / corneal flap under the same degree, the effect of different refractive error degrees on postoperative corneal biomechanical changes is mainly achieved indirectly by affecting the amount of corneal cutting. Although there were differences in preoperative SE, there were no significant differences in the amount of corneal cutting, the thickness of the remaining corneal stromal bed and the preoperative biomechanical parameters between the two groups. Therefore, it can be considered that the difference in preoperative SE has no effect on the validity of the research results.

[0080] Table 1 Baseline data of included patients

[0081]

[0082] (Note: CCT: Central corneal thickness measured by contact A-ultrasound; IOPNCT: Intraocular pressure measured by non-contact tonometry; RST: Residual stromalbed thickness; SE: Spherical equivalent)

[0083] Table 2 Comparison of preoperative baseline data between the two groups

[0084]

[0085] (Note: IOPNCT: intraocular pressure measured by non-contact tonometry; IOP: Corvis-ST jet intraocular pressure; BIOP: Corvis-ST biomechanically corrected intraocular pressure; CCT: central corneal thickness measured by contact A-ultrasound; RST: residual stromal bed thickness; SE: spherical equivalent)

[0086] Table 3 Comparison of baseline data of corneal biomechanical parameters before surgery between the two groups of patients

[0087]

[0088] SSI: Stress Strain Index; A1T, A1L, A1V: the first applanation time / length / velocity; A2T, A2L, A2V: the second applanation time / length / velocity; PD: Peak distance; DA: Deformation Amplitude; DARatio: Deformation Amplitude Ratio; HCRadius: Radius of corneal curvature at highest concavity; HCT: Time from the measurement beginning to the moment of reaching the highest concavity; IRA: Integrated Radius; ARTh: Ambrosio Relational Thickness in the horizontal direction SP-A1: corneal hardness parameters at the first press (the same below)

[0089] 2. Correlation analysis between preoperative corneal biomechanical properties and general parameters

[0090] Preoperatively, SSI was significantly correlated with the other 14 major Corvis-ST corneal biomechanical indices included in the analysis (P<0.05). As shown in Table 4, SSI was not related to age or CCT (P>0.05), but was significantly correlated with IOP. NCT , IOP, and BIOP were significantly positively correlated (correlation coefficients were 0.361, 0.312, and 0.255, respectively, P < 0.01, see Figure 4) Among the other main Corvis-ST corneal biomechanical parameters included in the analysis, except for HCT and ARTh, the remaining 12 related corneal biomechanical indices were significantly correlated with intraocular pressure (P<0.01). Except for HCT and A2T, the remaining 12 biomechanical indices were significantly correlated with CCT (P<0.01).

[0091] Table 4 Correlation between preoperative biomechanical parameters and general parameters

[0092]

[0093] (Note: *Significant correlation at the P<0.05 level; **Significant correlation at the P<0.01 level)

[0094] 3. Changes and trends of corneal biomechanics before and after two surgical methods

[0095] 3.1 Changes and trends of SSI

[0096] Intra-group comparisons of SSI values at three time points in the two groups were performed respectively. The results showed that there were significant differences in SSI values at different time points between the two surgical methods (P<0.01). In the inter-group comparison, there were no significant differences in SSI values between the two groups at the three follow-up visits of preoperative, 1 month after surgery, and 3 months after surgery (P>0.05). Pairwise comparisons of SSI at three time points in the two groups were performed respectively. The results showed that there were significant differences in SSI between 1 month after surgery and 3 months after surgery and preoperative in both groups (P<0.05), and it was significantly lower than preoperative after surgery (Table 5). There was an increasing trend in SSI from 1 month after surgery to 3 months after surgery ( Figure 8 -A), but the difference was not statistically significant (P>0.05).

[0097] Table 5 Comparison of SSI changes before surgery, 1 month after surgery, and 3 months after surgery between two surgical methods

[0098]

[0099] (Note: For intra-group comparison of measurement data conforming to normal distribution, repeated measures analysis of variance was used, and for non-normal distribution, Friedman test was used; for inter-group comparison of data conforming to normal distribution, two independent samples t-test was used, and for non-normal distribution data comparison, rank sum test was used.) a : Significant difference compared with preoperative (P<0.01); b : Significant difference compared with preoperative (P<0.05))

[0100] 3.2 Changes and trends of other main Corvis-ST biomechanical indices

[0101] Intra-group comparisons were made for other major Corvis-ST corneal biomechanical parameters of the included studies. Repeated measures analysis of variance was used for measurement data conforming to a normal distribution, and the Friedman test was used for non-normal distribution data. The two groups were compared separately. The results showed that except for the HC time, there were significant differences in other parameters at the three time points (P<0.01), and the same results were presented for the two surgical methods. Post hoc pairwise comparisons of the biomechanical indices at the three time points in the two groups found that at 1 month and 3 months after surgery, A1L, A2L, A2V, HC Radius, A1T, ARTh, and SP-A1 in both groups were significantly decreased compared with those before surgery, and A1V, PD, DA, A2T, DARatio, and IRA were significantly increased compared with those before surgery (P<0.05), all showing a decrease in corneal biomechanical stability. Except for ARTh in the FS-LASIK group, all indices reached stability at 1 month after surgery (the difference between 1 month and 3 months after surgery was not statistically significant, P<0.05). As Figure 8 shown and Tables 6 and 7 describe the changes in each index after the two surgical methods.

[0102] Table 6 Pairwise comparisons of changes in each biomechanical parameter within the SMILE group at each time point

[0103]

[0104]

[0105] (Note: *Significant difference at the P<0.05 level; **Significant difference at the P<0.01 level)

[0106] Table 7 Pairwise comparisons of changes in each biomechanical parameter within the FS-LASIK group at each time point

[0107]

[0108] (Note: *Significant difference at the P<0.05 level; **Significant difference at the P<0.01 level)

[0109] 4. Influence of the two surgical methods on corneal biomechanics

[0110] The change amounts of HC Radius, DARatio, IRA, ARTh, and SP-A1 in the SMILE group at 1 month and 3 months after surgery were significantly lower than those in the FS-LASIK group (P<0.05), and there was no significant difference in the postoperative change amount of SSI between the two groups (P>0.05). On the premise that there was no difference in the baseline data of each biomechanical parameter before surgery, PD, DA, DARatio, and IRA in the SMILE group at 1 month and 3 months after surgery were lower than those in the FS-LASIK group, while A2L, A1T, HC Radius, ARTh, and SP-A1 were higher than those in the FS-LASIK group, and the differences were statistically significant (P<0.05). (Tables 8, 9).

[0111] Table 8 Comparison of the change amounts of each biomechanical index after surgery in the two groups

[0112]

[0113] (Note: For the comparison between groups of data conforming to the normal distribution, the two-independent-sample t-test was used, and for the comparison of data not conforming to the normal distribution, the rank sum test was used; * at the P<0.05

[0114] level, the correlation was significant; ** at the P<0.01 level, the correlation was significant)

[0115]

[0116]

[0117]

[0118] (Note: For the comparison between groups of data conforming to the normal distribution, the two-independent-sample t-test was used, and for the comparison of data not conforming to the normal distribution, the rank sum test was used; * at the P<0.05 level, the correlation was significant; ** at the P<0.01 level, the correlation was significant)

[0119] Discussion

[0120] 1. Related influencing factors of SSI

[0121] The research and development of SSI, a new Corvis-ST corneal biomechanical parameter that reflects the hardness of corneal materials, aims to help solve two major problems in in vivo corneal biomechanics measurement. First, the nonlinear mechanical characteristics of corneal materials make the tangent modulus of the cornea not a fixed value, and different strain responses will occur under different stress conditions. Therefore, it is impossible to use a fixed value to reflect the material hardness of the cornea; second, the mutual influence between corneal biomechanics and many factors such as intraocular pressure, corneal thickness, and corneal morphology makes it difficult to independently evaluate the biomechanical properties of the cornea clinically. The SSI algorithm was verified through two large clinical data evaluations and was confirmed to be unrelated to CCT and intraocular pressure, but related to age. However, in existing studies, the correlation between SSI and CCT, intraocular pressure, and age is still controversial.

[0122] 1.1 Correlation between preoperative SSI, CCT, and intraocular pressure

[0123] In our study, SSI was not related to CCT, while biomechanical indices such as A1T, A1L, A1V, A2L, A2V, PD, DA, DA Ratio, HCRadius, IRA and another important parameter reflecting corneal hardness, SP-A1, were significantly correlated with CCT and intraocular pressure. This confirms that SSI has certain advantages over other biomechanical indices in independently reflecting corneal material hardness, especially after corneal refractive surgery. Due to the destruction of corneal collagen fibers and changes in corneal thickness, the evaluation of postoperative corneal biomechanics has always been a major problem. The characteristic of SSI that is not affected by corneal thickness helps clinicians to make an objective evaluation of postoperative corneal material hardness, and has important clinical value for the diagnosis of patients with postoperative corneal ectasia and the evaluation of the effects of different refractive surgery methods and different surgical designs on corneal biomechanics.

[0124] There was a weak correlation between SSI and BIOP and CCT.

[0125] In this example, the intraocular pressure data obtained by different intraocular pressure measurement methods were statistically analyzed, and it was found that SSI was significantly correlated with IOP measured by non-contact intraocular pressure measurement instrument, IOP measured by Corvis-ST, and BIOP. However, when comparing the intraocular pressures obtained by the three measurement methods, the correlation between SSI and BIOP was higher than that between IOP and SSI. NCT , IOP is relatively weaker.

[0126] BIOP is a biomechanically corrected intraocular pressure provided by Corvis-ST. Compared with uncorrected intraocular pressure, BIOP has been proven to be closer to the true intraocular pressure value and less affected by corneal mechanical hardness, CCT and age. The SSI algorithm uses BIOP and CCT for correction to eliminate the influence of the two on corneal hardness measurement.

[0127] Our results show that although the correction of SSI using BIOP has a certain effect, the correlation between SSI and BIOP is weak but still significant, indicating that intraocular pressure and corneal hardness are still inseparable. This is consistent with our previous experience that the measurement of corneal biomechanics cannot be completely independent of intraocular pressure. High intraocular pressure will show a stronger corneal material hardness. Conversely, differences in corneal thickness and corneal hardness will also affect accurate intraocular pressure measurement. To obtain corneal material hardness parameters that are not affected by intraocular pressure, the SSI algorithm still needs to be further improved.

[0128] 1.2 Correlation between preoperative SSI and age

[0129] In previous studies, age has been shown to be an important factor affecting corneal biomechanics, but our study did not find a correlation between SSI and age, which can be explained by the narrow age distribution of the included data population. The average age of the population included in this example is 24.54±5.10 years old. In vitro measurement studies have found that the growth rate of the tangent modulus of the cornea is smaller in young people, indicating that corneal biomechanics may show nonlinear changes with age. It was found that the biomechanics of healthy people under 40 years old is not related to age, and SSI increases with age after 35 years old.

[0130] It is currently believed that this change is similar to the increase in hardness of other human tissues such as the aorta and cartilage with age. The diameter and number of corneal collagen fibers, glycosylation reactions, and non-enzymatic cross-linking reactions all increase with age, while the content of glycosaminoglycans in the extracellular matrix decreases, the gap between collagen fibers decreases, and the hydration stability of the cornea decreases, resulting in corneal hardening. However, since the hardness of the corneal material changes unevenly and nonlinearly with age, the correlation between SSI and age is not significant in younger people.

[0131] 2. Changes in corneal biomechanics after SMILE and FS-LASIK

[0132] A study on the changes in various corneal biomechanical indicators including SSI before and after surgery found that the corneal biomechanics of the two surgical methods underwent significant changes. Except for HCT, the biomechanical indicators including SSI showed significant differences between before and after surgery. SSI, A1L, A2L, A2V, HC Radius, A1T, ARTh, and SP-A1 at 1 month and 3 months after surgery were significantly decreased compared with those before surgery, while A1V, PD, DA, A2T, DA Ratio, and IRA were significantly increased compared with those before surgery. After corneal refractive surgery, the cornea is more easily indented and the depth of indentation increases due to the decrease in corneal tensile strength and stiffness. Therefore, the indicators such as A1V, PD, DA, DARatio, IRA, HC Radius related to the first flattening and the maximum concave state increase, while the indicators such as A1T and A1L decrease. Due to the decrease in corneal elastic retraction force, the cornea rebounds from the maximum concave state to the second flattening and then returns to the original state, and A2T increases, while A2V and A2L decrease. Due to the significant decrease in corneal thickness and the decrease in the hardness of corneal materials, the parameters reflecting corneal hardness such as ARTh, SP-A1, and SSI also decrease significantly. The changes in these indicators indicate a decrease in corneal biomechanical stability after surgery. Although preoperative SSI is not related to CCT, it still shows a significant decrease after surgery, because the hardness of corneal materials is not determined by a single factor, corneal thickness, but is affected by multiple factors such as corneal geometry, collagen fiber arrangement and stability, and corneal curvature. The change in the hardness of corneal materials after surgery is more due to the damage of surgery to corneal collagen fibers and corneal mechanical strength rather than simply caused by changes in corneal thickness. HCT did not change significantly after both surgical methods. The possible reason is that the mechanical strength of the cornea is weakened after surgery. When subjected to Corvis-ST air pulses, the ability to resist corneal deformation caused by external forces is weakened, which makes the depth of the cornea when it reaches the maximum depression larger. Therefore, although the cornea is more likely to be depressed after surgery, the time from the cornea starting to contact the airflow to reaching the maximum depression has not changed significantly. The same reason also leads to no significant correlation between HCT and corneal thickness and intraocular pressure. The results of this embodiment show that HCT does not provide ideal clinical value in reflecting the low strength of the cornea against external forces.

[0133] In addition, we found that the biomechanical indices that changed significantly after surgery mainly changed at the first follow-up one month after surgery. There was no significant change between three months after SMILE surgery and one month after surgery. Except for ARTh after FS-LASIK surgery, there was no significant difference between three months after surgery and one month after surgery for other indices. Figure 5As shown in the data, SSI decreased significantly in both surgical methods one month after surgery, and increased slightly three months after surgery compared with one month after surgery, but the difference was not statistically significant. In the case of no significant difference in the baseline of the preoperative biomechanical parameters, the PD, DA, DARatio, and IRA of the SMILE group were significantly lower than those of the FS-LASIK group one month and three months after surgery, and the A2L, A1T, HC Radius, ARTh, and SP-A1 were significantly higher than those of the FS-LASIK group. We believe that after corneal refractive surgery, corneal biomechanics will undergo a repair process with the reconstruction of tissues and the healing of collagen. The cornea will reach a new biomechanical balance and re-establish a stable biomechanical state after surgery. This steady state may occur within one month after surgery, and the SMILE group has a better effect of corneal biomechanical reconstruction than the FS-LASIK group. The study found that substantial changes in corneal biomechanics measured by Corvis-ST after SMILE only occurred at the first follow-up 7 days after surgery. In addition, several studies using an eye response analyzer to measure corneal biomechanics found that the CRF (Corneal resistance factor) value continued to decrease 1 month after FS-LASIK surgery and reached stability only 3 months after surgery;

[0134] In the early stage after SMILE surgery, the CRF and CH (Corneal hysteresis) values ​​were significantly lower than those before surgery, but there was no significant change in the CRF and CH values ​​of the operated eyes from 1 month to 12 months after surgery. This may indicate that the corneal biomechanics after SMILE surgery reaches stability earlier than after FS-LASIK surgery. However, these studies did not compare the two surgical methods.

[0135] Tissue healing after SMILE surgery is earlier than that after LASIK, and SMILE surgery can reshape the corneal biomechanical strength better. However, our study did not find any difference in the time it takes for the corneal biomechanical recovery to reach stability between the two surgical methods.

[0136] Since the postoperative follow-up time in this example was designed to be 1 month and 3 months after surgery, the changes in corneal biomechanics beyond 3 months after surgery were not observed. However, most postoperative corneal ectatic diseases occur several months to years after surgery. Therefore, longer follow-up will be needed in the future to observe the long-term changes in corneal biomechanics after surgery and compare the differences in corneal biomechanical strength remodeling between different surgical methods.

[0137] 3. Differences in the effects of SMILE and FS-LASIK on corneal biomechanics

[0138] In the results of this embodiment, the changes in HC Radius, DARatio, IRA, ARTh, and SP-A1 at 1 month and 3 months after SMILE surgery were significantly lower than those after FS-LASIK surgery, and the differences were statistically significant. SMILE surgery is superior to FS-LASIK surgery in terms of postoperative biomechanical stability. The biomechanical properties of corneal tissue are affected by many factors such as corneal tissue structure, intraocular pressure, corneal thickness, age, hormone levels, etc. There are also differences in the biomechanical properties of each layer of the cornea, which makes the effects of different corneal refractive surgeries on postoperative corneal biomechanics also different. We generally believe that the content, arrangement, and interaction of collagen fibers and proteoglycans in the corneal stroma are closely related to the biomechanical properties of the cornea, and are the most important part affecting the biomechanical strength of the cornea, and the anterior stroma bears more mechanical effects than the posterior stroma. The anti-tensile strength of the anterior 40% of the corneal stroma is significantly higher than that of the posterior 60% of the corneal stroma. Therefore, although both SMILE and FS-LASIK surgeries perform refractive cutting on the corneal stroma, SMILE better preserves the corneal stroma with stronger tensile strength due to the thickness of the corneal cap. In addition, there is no flap-making process and the incision is small during SMILE, which more completely preserves the integrity of the corneal tissue structure. Compared with FS-LASIK, it usually leads to less keratinocyte apoptosis, less proliferation, less inflammation, and faster nerve density regeneration, so it has less impact on the biomechanics of the cornea. However, in terms of corneal hardness reflected by SSI, there is no significant difference between the two surgical methods in the hardness characteristics of the corneal material after surgery.

[0139] This embodiment has several limitations. First, SSI is developed based on the healthy cornea of ​​the normal population. In the case of artificial changes in corneal biomechanics after refractive surgery, the effectiveness of SSI measurement needs to be considered. Second, the possible effects of different corneal cap (corneal flap) thicknesses and different optical zone sizes on corneal biomechanics in the surgical design were not considered during the experimental design. The consistency of the parameters of the patient's surgical design was not controlled. Instead, the surgical design was performed based on the patient's own situation while considering retaining the residual thickness of the safe corneal stroma layer, which may have a certain impact on the research results. Third, the bias caused by intraocular pressure measurement at different time points was not ruled out. Since measuring intraocular pressure at different time periods will affect the intraocular pressure value, the research results related to intraocular pressure should be analyzed objectively and cautiously, and it is hoped that they will be improved and supplemented in future research.

[0140] in conclusion

[0141] As a corneal hardness parameter that is considered to be independent of CCT and IOP, SSI is expected to provide an independent and effective corneal material hardness evaluation index for clinical use. This example confirms that SSI is independent of CCT and weakly correlated with intraocular pressure. SSI has certain advantages over other biomechanical indicators in independently reflecting corneal hardness, but its limitations cannot be ignored. The correlation between SSI and intraocular pressure and its applicability in different populations and corneas of different states still need to be further improved.

[0142] SSI and other major corneal biomechanical indices were significantly reduced after both surgical procedures and reached a new biomechanical balance after surgery. SMILE surgery was superior to FS-LASIK surgery in terms of postoperative corneal biomechanical stability, but there was no significant difference in the effect on SSI.

[0143] Clinically, in the evaluation of corneal biomechanics before and after surgery, corneal morphology, intraocular pressure, corneal curvature, corneal thickness, intraocular pressure, etc. must be comprehensively considered. Currently, there is no single independent indicator that can represent the biomechanical properties of the cornea. The advantage of SSI in measuring the material properties of the cornea itself is conducive to clinical physicians making an objective assessment of corneal hardness. Clinicians fully understand the characteristics of various biomechanical indicators and the effects of different surgical methods on corneal biomechanical properties, which helps to conduct personalized biomechanical assessments of patients to identify susceptible patients with corneal ectatic diseases and conduct personalized biomechanical optimization surgical designs.

[0144] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0145] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A system for detecting corneal stress changes after refractive surgery, characterized in that: The system comprises: a. Data input module, used to receive the patient's basic information and corneal biomechanical parameters before and after surgery; b. Data processing module, used to analyze the input corneal biomechanical parameters and calculate the corneal stress strain index (SSI); c. Data storage module, used to store basic patient information, pre- and post-operative corneal biomechanical parameters, and calculated SSI; d. Result output module, used to display the detection results of corneal stress changes.

2. The post-operative corneal stress change detection system according to claim 1, characterized in that: The data processing module comprises: a. Finite element (FE) numerical model to simulate the effects of intraocular pressure and Corvis-ST air jet on the cornea; b. Numerical estimation unit, used to perform numerical estimation based on the prediction results of the FE model by the least square method; c. Algorithm validation unit, used to evaluate the correlation of the algorithm with intraocular pressure, central corneal thickness (CCT) and age through a clinical database.

3. The post-refractive surgery corneal stress change detection system according to claim 1, characterized in that: The data input module further comprises: a. Patient basic information input interface, including but not limited to the patient's age, gender and surgical method; b. Biomechanical parameter input interface, used to input preoperative and postoperative corneal biomechanical parameters.

4. The post-refractive surgery corneal stress change detection system according to claim 1, characterized in that: The data storage module adopts a database management system for organizing and indexing stored data.

5. The system for detecting corneal stress changes after refractive surgery according to claim 1, characterized in that: The result output module includes: a. Graphical user interface (GUI) for displaying visualization results of corneal stress changes; b. Report generator, used to generate detailed reports containing test results.

6. The working method of the post-refractive surgery corneal stress change detection system according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: a. Receive the patient's basic information and pre- and post-operative corneal biomechanical parameters through the data input module; b. Analyze the input corneal biomechanical parameters and calculate SSI using the data processing module; c. storing the patient's basic information, preoperative and postoperative corneal biomechanical parameters and the calculated SSI in the data storage module; d. Display the detection results of corneal stress changes through the result output module.

7. The working method of the post-refractive surgery corneal stress change detection system according to claim 6, characterized in that: In step b, the analysis process of the data processing module includes: a. Use FE numerical model to simulate the effect of intraocular pressure and Corvis-ST jet on cornea; b. Perform numerical estimation based on the prediction results of the FE model using the numerical estimation unit; c. The correlation between the algorithm and intraocular pressure, CCT and age was evaluated through the algorithm verification unit.

8. The working method of the post-refractive surgery corneal stress change detection system according to claim 6, characterized in that: In step b, the calculation steps of SSI are: The finite element FE numerical model simulates intraocular pressure and Corvis-ST jet. Based on the prediction of the corneal deformation response of Corvis-ST, the central corneal thickness CCT, biomechanically corrected intraocular pressure BIOP and the corneal hardness parameter SP-HC at maximum concave are used as input and output parameters for numerical simulation. The least squares method is used for numerical estimation, and then the algorithm is verified by the correlation between the algorithm evaluated by two large clinical databases and intraocular pressure, CCT and age. Finally, an index SSI reflecting the hardness of the corneal material is obtained.

9. The working method of the post-refractive surgery corneal stress change detection system according to claim 8, characterized in that: In step b, the SSI is calculated as follows: the Corvis-ST aimed air pulse can produce a constant maximum pressure pump, ensuring that the dynamic deformation response of the cornea is comparable among different individuals; The Scheimpflug ultra-high-speed imaging system can capture 4430 frames of images per second. Within 31ms of the start of the air pulse, the high-speed camera can capture 140 frames of horizontal cross-sectional images of the cornea, which can completely and clearly describe the entire process of the cornea's dynamic deformation response, including the cornea's initial convex state to the air pulse flattening the cornea into the concave phase and reaching the maximum depression state, and finally returning to the original shape. Corvis-ST measures the cornea's dynamic deformation response in the pre-deformation phase, inward movement convex phase, inward movement concave phase, oscillation phase, outward movement concave phase, outward movement convex phase, and posterior corneal flexion phase.

10. A computer-readable storage medium, characterized in that: The medium has a computer program stored thereon, the program being configured to execute the steps of the method according to claim 6.

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