Modeling Of The Stress-Free Configuration Of Corneal Structure By Computational Methods. A Comparative Study.

To evaluate the preliminary stress distribution in the mediating phase physiological structure of the cornea basing on inverse iterative methods.

Study performed in the National Network of Cooperative Research in Ophthalmology (RETICS), Universidad Politécnica de Cartagena, Spain.

Two Finite Element Method models were developed based on healthy physiological (G0) and incipient keratoconus (G1) geometries, according to the RETICS classification. The models were considered with 3D elements type Solid 186 with 4 elements of thickness and 4 corneal regions. A model of anisotropic hyper-elastic material without loss of viscosity was considered. Displacement and pre-stress methods were used to obtain inverse geometry and deformation maps. Intraocular pressures (IOP) measured in clinical practice were applied.

The stress distributions for physiological IOPs for corneas G0 (18 Pa) and G1 (16 Pa) were very similar for the two implemented methods. The average maximum values obtained in the central zone for groups G0 and G1 were 19.571 Pa and 19.602 Pa respectively. The average elastic module tangent in the central zone for the stress and strain values was the same for both methods (0.366 Pa).

The displacement and pre-stress methods are equivalent and achieve the same stress distribution in the measurement phase for the corneas analysed. From a computational point of view, the displacement method involves fewer iterations and is therefore more efficient (+12%), and allows to obtain the shape-free geometry directly. Knowledge of free geometry and stress distribution in the measurement phase is an important factor in improving the accuracy of in silico biomechanical models. These computational simulations could aid the development of patient-specific models and in the improvement of the efficiency of surgical procedures in ophthalmology.