Study On The Biomechanical Properties Of Human Cornea Based On The Uniaxial Tensile Test

Refractive error has become one of the most common diseases in the Department of Ophthalmology.In recent years,with the rapid development of modern corneal refractive surgery,a large number of laser treatment techniques for myopia have emerged.Small incision lenticule extraction（SMILE）corneal refractive surgery,as a new surgical method,has become the focus of attention in recent years.Although this new technique has provided satisfactory refractive outcomes,predictability,and stability in most published reports,the complications after surgery still have not been solved.The principle of SMILE corneal refractive surgery is to change the refractive power of the cornea by extracting a part of the cornea.The refractive surgery changes the integrity of the cornea,resulting in changes in the biomechanical properties of the cornea.To predict the deformation and internal force of cornea after the SMILE corneal refractive surgery,one of the important research topics of corneal biomechanics is the determination of constitutive parameters.The cornea stromal lenticules used in this paper were from the SMILE corneal refractive surgery.The biomechanical behavior of human corneal stroma under uniaxial tension was investigated by the experimental analysis and finite element simulation.The corneal specimens were collected from 34 patients（11 male and 23 female）,aged from 17 to 39 years old.In order to determine corneal anisotropy,pairs of lenticules were extracted from two eyes of the same human and used to produce specimens in different anatomical directions.Uniaxial tensile tests were conducted to determine corneal stress-strain relationship and tensile strength.The differences between corneal stress-strain relationship and tensile strength in the horizontal and vertical direction were compared.The hyperplastic constitutive theory of cornea is reviewed.Based on the microstructure of cornea,the Gasser-Ogden-Holzapfel（GOH）model was used to describe biomechanical behavior of the cornea.The theoretical stress-strain relationship of the GOH model in the uniaxial tensile test was deduced.The constitutive parameters C₁₀,k₁ and k₂ were evaluated through least squares curve-fitting of experimental data.Based on the geometric parameters of the cornea and the ablation function of the refractive surgery,the three-dimensional finite element model of the cornea and corneal lenticule were established.The Holzapfel constitutive model in ABAQUS software was used to verify the accuracy of the material parameters obtained by the simulation of the uniaxial tensile test.The influence of different fitting methods on the material parameters of GOH model were compared by simulating inflation experiments of cornea and corneal lenticule,and the material parameters of the numerical model were determined.The three-dimensional finite element model of the cornea after SMILE was established.The material parameters obtained by the uniaxial tensile test were used in the numerical simulation,and the change of the corneal posterior surface displacement difference was analyzed.