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J. F. Bille, H. Zhang; Finite Element Model of the Human Cornea for Simulation of Intrastromal Laser Refractive Surgery. Invest. Ophthalmol. Vis. Sci. 2008;49(13):668.
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To develop a three-dimensional, non-linear, non-homogeneous finite element model of the human cornea to estimate three-dimensional stresses and finite strains in the cornea.
Finite element modeling method is used to study the biomechanical properties of the cornea. Three-dimensional spherical polar coordinates are used to avoid membrane or shell theories and minimize the number of degrees-of-freedom needed to obtain converged solutions. 144 three-dimensional elements are used in the current model and each element is associated with 8 nodes. The cornea is assumed to be a slightly compressible, non-linear, non-homogenous material. The whole cornea is divided into 9 layers (3 layers for Bowman’s layer and 6 layers for stroma) and Bowman’s layer is assumed to be stiffer than stroma. Intraocular pressure is applied homogeneously to the posterior layer of the cornea during the simulation. A new boundary condition is proposed and applied in the current model that only Bowman’s layer is fully fixed instead of the whole cornea at the limbus.
Intraocular pressure (IOP) is simulated to be increasingly applied to the cornea from 0 kPa (stress-free state) to 4 kPa and the corresponding apical rise is calculated by finite element analysis. The "Apical-rise vs. IOP" curve shows a good agreement with the published experimental data. Three-dimensional stresses and strains at the center of each element are calculated under normal IOP (2 kPa) and abnormal IOP (4 kPa). Three locations (apex, mid-section and near-limbus) in the cornea are chosen for further quantitative evaluation. 3-D stresses and strains within Bowman’s layer and stroma are also evaluated. The boundary conditions at the limbus are varied to study how such clamping conditions affect the stress and strain estimates.
A new three-dimensional, non-linear, heterogeneous finite element model of the human cornea has been established to study the biomechanics of the cornea, which is important for choosing proper surgical parameters and predicting post-operative outcomes.
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