Modeling and Biomechanical Analysis of Keratoconus

Keratoconus is a non-inflammatory ocular disorder in which the cornea bulges in the shape of a cone. Therefore, this progressive disease will cause visual impairment. The precise aetiology of keratoconus is not well understood. Investigating the pathogenesis of keratoconus from a biomechanical point of view will determine which biomechanical factor plays the dominant role in keratoconus formation. In this study, using the finite element method, a three-dimensional model of the human cornea with anatomical dimensions was created, and hyperelastic isotropic properties were assigned to it. Then, the inner surfaces of the model were subjected to physiological intraocular pressure. This model was regarded as a healthy cornea and as a reference model. Then, two symmetric and asymmetric states of keratoconus were simulated. For this purpose, a circular region was created in the center of the cornea (for the symmetric state) or in one of its quarters (for the asymmetric state), and then, in this circular region (i.e., locally), the following operations were performed with three different intensities to simulate three different stages of symmetric/asymmetric keratoconus: 1) reducing the thickness, 2) weakening the mechanical properties, and 3) reducing the thickness and weakening the mechanical properties, simultaneously. By analyzing the displacements, it was found that the local weakening of the mechanical properties makes the cornea significantly steep in the area affected by the disease and causes keratoconus formation. Therefore, in keratoconus formation, the weakening of mechanical properties plays a primary role, and the reduction of thickness plays a secondary and auxiliary role.