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Julien Bullet, Morgane Bauer, Vincent Borderie, Stéphane Roux, Laurent Laroche; A Mechanical Modelling Approach To Porcine Eye Cornea. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1513.
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Overall corneal biomechanical parameters commonly used today have limited reproducibility and clinical reliability. The present work aims at proposing a different methodology of measurement for corneal mechanical properties based on a precise finite element model. It is limited to porcine enucleated eyes
A freshly enucleated pig eye is mounted on a support with anterior chamber perfusion, in order to control intraocular pressure. To check endothelial viability, central corneal thickness is measured and remains stable during experiment. 3D geometrical characterization of cornea is achieved at rest and under different load conditions (IOP variation) through a rotating slit illumination combined with a Scheimpflug camera system (Oculus Pentacam).From detailed anterior and posterior surface maps and central corneal thickness at rest reference state, a mechanical model of the cornea using the finite element method (Abacus code) is built. Regular elastic mechanical laws are used to deduce final displacement field with increasing IOP load. Comparing this calculated displacement with measured corneal 3D map, boundary conditions as well a biomechanical corneal characteristics such as Poisson coefficient and Young modulus are estimated (least square optimization with Matlab software). To minimize the number of unknowns to be identified, only few Fourier series decomposition terms of boundary conditions are computed.
Figure 1 shows the deformed geometry of a cornea after a slight increase in intra-ocular pressure, and Figure 2 is a comparison between predicted and measured model after optimization of boundary conditions.
Results presented in Figure 2 show that the difference between measured and calculated geometry is in the tens of micrometer range, or about 2% of the dynamics. However, cornea is here considered as purely elastic with simple mechanical laws. Viscosity can be excluded from model as only dynamically balanced states are simulated.This first simple mechanical model of cornea demonstrates that the chaining of experiment, data acquisition, and modeling works. Other more sophisticated models including other load conditions, viscosity or other imaging techniques are to be developed.
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