P. Ruzicka and S. Konvickova (Czech Republic)
Cornea, mechanical properties, thermal shrinkage, laser thermokeratoplasty, finite element method
Laser thermokeratoplasty (LTK) is the ophthalmologic procedure used for the hyperopia correction. Corneal collagen is heated up and coagulated by application of the laser beam. The induced traction within cornea increases cornea curvature. The aim of the project is to create three-dimensional model of the human cornea, to simulate the LTK procedure using finite element method. Identification of corneal tissue mechanical properties and response to the thermal excitation is necessary to form mathematical model. Thus tensile tests of porcine corneal tissue stripes were conducted. The model of fibre-reinforced material is applied to respect layered structure of the cornea. Incompressible hyperelastic material models are applied, the Mooney-Rivlin model for extrafibrillar proteoglycan substance and the model with the second order reduced polynomial form of strain energy for two families of collagen fibres. The effect of thermal shrinkage of cornea tissue is simulated by FEM as thermal shrinkage of collagen fibres and coefficients of thermal expansion were identified to fit experimental observations. Results of two simulations of LTK are presented, the case of spherical refractive error correction and the case of regular astigmatism correction. The computation results confirm good correspondence of the finite element model with the actual cornea remitted to LTK.
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