Numerical Analysis Of Corneal Deformation And Internal Force Before And After Two Kinds Of Corneal Refractive Surgery

Myopic has become one of the most common diseases in Ophthalmology,and its incidence is increasing year by year.Refractive surgery is an important way of treat myopia,which is done by ablation of the thickness of the cornea on the cornea to correct vision.Cornea,as a composite soft material,the refractive surgery change the original integrity of the cornea.Different refractive surgery results in a greater difference in biomechanical performance of the cornea.Now,the study of corneal biomechanics focuses on the collection and analysis of corneal dynamic parameters,and no quantitative analysis of the deformation and internal forces of the cornea.This work is based on the development of refractive surgery and the research on biomechanics,To investigate the deformation and internal force of cornea after small incision lenticule extraction(SMILE),explore the corrected diopter and preoperative corneal thickness effects on postoperative corneal biomechanical characteristics,compared with the mechanical behavior of laser in situ keratomileusis(LASIK).and analyzed the effect of the geometrical state of the small incision on the biomechanical behavior of SMILE.The Gasser-Holzapfel-Ogden hyperelastic constitutive describe the mechanical behavior of the corneal material.Preoperative and postoperative corneal finite element models were established.Using To calculate the difference of the displacement of the central point of the corneal posterior surface after two operations,and analyzing different corrective diopter and preoperative corneal thickness effects on postoperative corneal deformation and internal force.Before and after SMILE surgery,the difference of the central point displacement of the posterior corneal surface increased linearly with the corrected diopter,and LASIK surgery showed a large nonlinear increment.The effect of preoperative corneal thickness on the posterior surface of the cornea was lower when the corrective diopter was small,and the effect was increaseing obvious when the corrected diopter was higher.Compared with LASIK surgery,corneal deformation and Mises stress were smaller after SMILE surgery.Using linear elasticity model and hyperelastic model described the mechanical behavior of corneal material.And analyzed the effects of the two models on the posterior deformation and internal force distribution of the cornea under normal intraocular pressure.The results showed that the effects of the two models on the posterior corneal surgery were same.The stress distribution at the central point of the posterior cornea was stable under different corrected diopter.Small incision radians will cause stress concentration in different positions of the cornea.SMILE corneal deformation and internal force changes by corrective diopter,preoperative corneal thickness effect is smaller compare with LASIK,in this paper,the finite element analysis results provide numerical basis for the assessment of the biomechanical analysis of two kinds of surgical and surgical results.