Abstract
A finite element method was used to study the biomechanical behavior of the cornea and its response to refractive surgery when stiffness inhomogeneities varying with depth are considered.
Side-by-side comparisons of different constitutive laws that have been commonly used to model refractive surgery were also performed. To facilitate the comparison, the material property constants were identified from the same experimental data, which were obtained from mechanical tests on corneal strips and membrane inflation experiments. We then validated the resulting model by comparing computed refractive power changes with clinical results.
The model developed provides a much more predictable refractive outcome when the stiffness inhomogeneities of the cornea and nonlinearities of the deformations are included in the finite element simulations. Thus, it can be stated that the inhomogeneous model is a more accurate representation of the corneal material properties in order to model the biomechanical effects of refractive surgery. The simulations also revealed that the para-central and peripheral parts of the cornea deformed less in response to pressure loading compared to the central cornea and the limbus. Furthermore, the deformations in response to pressure loading predicted by the non-homogeneous and nonlinear model, showed that the para-central region is mechanically enhanced in the meridional direction. This result is in agreement with the experimentally documented regional differences reported in the literature by other investigators.