Abstract

Objective To establish a biomechanical finite element model of myopic laser in situ keratomileusis (LASIK) and to study the relationship between various parameters and the elevation change of posterior corneal surface.Methods Computer numerical simulation study.Sixty-eight subjects (116 eyes) were measured with Orbscan ⅡZ corneal topography system.Selecting 110 eyes randomly from 116 eyes,all special points' coordinates of the 110 corneas were introduced to SAS statistical software to calculate the corneal surface equations through non-linear regression method and to compare the forecast results with the actual values.Constructing the corneal 3D model by ANSYS software,simulating LASIK by mathematical method,setting up biomechanical parameters,restraining boundary conditions,loading capacity,establishing the laser refractive corneal surgery model based on the biomechanical properties.The Z-axis displacement of posterior corneal surface apex was used as an observing index.Results The general equation of the anterior surface:X2/8.78+Y2/8.68+(Z+9.79)2/9.792=1 (Residual=115.50,R2=0.99),posterior surface:X2/8.40+Y2/8.19+(Z+ 11.89)2/11.352=1(Residual=96.63,R2=0.99).The correlation r between the measured Z-axis values and predicted Z-axis values of anterior and posterior corneal surface were both 0.99.The Z-axis displacement of posterior corneal surface apex correlated positively with flap thickness,optical zone diameter,intraocular pressure,negatively with the modulus of elasticity and refractive errors correction in the surgery simulation.The parameter that had the most effect on the hyperopic shift of the posterior surface was the modulus of elasticity.Conclusion The myopia anterior and posterior corneal surfaces are both ellipsoid.The finite element model shows that the modulus of elasticity has the most effect on the hyperopic shift of the posterior surface.The study will be able to provide other relevant basic information. Key words: Keratomileusis,laser in situ; Cornea; Numerical simulation; Finite element analysis

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