Construction Of Cornea Sclera Constitutive Equation And SMILE Operation Finite Element Analysis

Myopia is currently the eye disease with the highest prevalence rate,the degree of myopia among adolescents in our country is increasing,and the age of the disease is gradually decreasing.Due to the irreversibility of myopia,there are no effective drugs or treatments to cure myopia,so the correction of myopia in adolescents can only be corrected by refractive surgery.Femtosecond Laser Small Incision Lens Removal(SMILE)is the most advanced and most clinically applied procedure in current refractive surgery,and it is the most potential method of myopia correction.However,the domestic equipment for SMILE surgery is imported from abroad,and it is impossible to obtain the parameter rules set by SMILE surgery and the changes of the postoperative cornea.Through the finite element simulation technology,the SMILE surgery can be simulated and simulated,the parameters that affect the effect of the SMILE surgery can be studied,the rules of the operation can be summarized,and the accuracy of the operation can be improved.In the finite element simulation of SMILE surgery,the determination of the corneoscleral constitutive model is the basis and focus of the simulation,which has a decisive influence on the accuracy of the simulation results.This paper studied the properties of the corneal and scleral material of the eyeball.The biaxial stretching experiment was used to stretch the human corneal lens and the porcine cornea.The experimental results showed that the greater the strain of the cornea,the more obvious the anisotropy.In the smaller deformation range of the cornea,it can be considered that the cornea was an isotropic material.At the same time,it was found that the material properties of the porcine cornea were very different from the material properties of the human corneal lens,and the material properties of the porcine cornea can be equated with the properties of the human cornea.The porcine eyeball was divided into cornea,anterior sclera,equatorial sclera,and posterior sclera specimens for uniaxial tensile measurement,and the stress-strain curve of the cornea was fitted to calculate the elastic modulus.The stress-strain curve and its own material properties were expressed using the Ogden secondary constitutive model to express the properties of the cornea,and the stress-strain data was processed to obtain the parameters of the Ogden constitutive model for each region of the cornea and sclera.A finite element simulation platform for SMILE surgical healing was constructed based on ABAQUS finite element simulation software.Through the analysis of the structure and organization of the eyeball,the geometric model of the eyeball was optimized and established;the geometric model was meshed with Hypermesh software,and the method of adjusting the element nodes and removing the internal elements of the mesh model was adopted to simulate the corneal lens extraction process.According to the internal and external forces of the eyeball,the boundary conditions were set to simulate the effect of the cornea on the intraocular pressure and the fixation effect of the extraocular muscles on the eyeball.Load was applied to the outer surface of the corneal cutting part to simulate the negative pressure when the cornea is healed.The actual eyeball parameter information obtained was imported into the finite element simulation platform for simulation,and the displacement of the central area of the outer surface of the cornea was used as the standard to measure the simulation result.The simulation result was good when the displacement was equal to the thickness of the cornea.According to the two standards of the fit of the inner and outer surfaces of the corneal cutting part and the size of the diopter area on the outer surface of the cornea,it was judged that the simulation results were consistent with the actual surgical results.Further analysis of the simulation results showed that the ratio of intraocularpressure to simulated negative pressure was about 1.776.Selectd the simulation parameters of the other six eyeballs into the finite element simulation platform for simulation,setted the negative pressure according to the previously determined rule,and compared the simulation results with the simulation results when the displacement of the central area of the outer surface of the cornea is equal to the thickness of the corneal lens,and it was found that the displacement difference of the central area of the cornea was very small,and the area error of the outer surface of the cornea meets the expected surgical error was less than 2%,which proved that there was a proportional relationship between the intraocular pressure and the corneal negative pressure.At the same time,the constructed finite element simulation platform for SMILE surgery was proved effective.