A number of studies have conducted different methods

to determine corneal biomechanical properties. M.A. Lago et al 48

developed a method to identify patient-specific mechanical properties using

finite element models. They assumed the cornea as a nonlinear elastic material.

For the

in vivo characterization of the elastic constants that describe the

biomechanical behavior of the human cornea.

Biomechanical model simulates the deformation of the

cornea in non-contact tonometry, where an air jet applying in corneal to

measure the IOP )figure18(. The simulation of the cornea deformation was performed using

the Finite Element Method (FEM).

A second-order hyperelastic Ogden model was chosen.

The energy potential function of the N-order Ogden model is defined in the

following equation:

A video sequence of the cornea deformation

obtained

by The Corvis ST device, figure19. Using the images of the deformed cornea from

this sequence, a search algorithm iterates over the elastic constants in order

to simulate a deformation that is as close as possible to the real deformed

cornea.

The estimated parameters in this study proved that

the methodology is able to obtain a biomechanical model that is very similar to

the target one.

The

differences between pixels observed a thin line of non- matching pixels

along the surface of the cornea see figure 20.

This methodology can be applied to any other

biomechanical model chosen to represent the behavior of the cornea, even adding

more complexity like considering anisotropy or viscoelasticity. The only

difference will be the number of parameters that the genetic algorithm has to

manage and the consequent computation time is necessary.

This methodology proved to be suitable in a simple

2D geometrical model of the cornea. A 3D geometry of the cornea which takes

into account the thickness variability from the center to the periphery would

increase the accuracy of the estimated biomechanical model.