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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).

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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
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




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.

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. 

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