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David Varssano, Roy Asher, Elad Moisseiev, Amit Gefen; Patient Specific Finite Element Cornea Model. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6892.
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Most biomechanical models of the cornea have been simplified geometric models not based on actual patient data. The few that were based on patient specific data are very complex and require highly capable computation hardware. Assuming that the clinician has access to the equipment needed to determine the patient's corneal topography, intraocular pressure (IOP) and modulus of elasticity, a simple patient-specific finite elements (FE) model could be easily developed. It was our interest to acquire a method for obtaining such a model.
Corneas of a healthy subject were sampled (Galilei, Ziemer) and IOP was measured. Then an intraocular pressure regulating medicine (dorzolamide hydrochloride and timolol maleate commercial combination) was introduced onto the right eye once. The sampling was repeated every two hours for the following six hours. Exported data included information about the corneal anterior and posterior height, curvature, pachymetrey and power maps. Matlab (Mathworks, Matlab) was used for analyzing, verifying and extrapolating the data to a full-length patient specific cornea. This was later transferred in the format of a cloud file into computer-aided design software where meshes and surfaces of the anterior and posterior surfaces were created and a solid cornea part was obtained .The part was then imported into a commercial FE analysis package where different IOPs could be set as boundary conditions.
Different IOP values resulted in corresponding stress and deformation maps of the patient specific cornea per each change in amplitude. Figure 1 displays the patient-specific cornea's maximum principal elastic strain output. (a) Anterior surface, (b) Posterior surface following application of 16mmHg IOP with the cornea constrained at the limbus region.
Integrating patient-specific data from equipment present in clinical settings into such FE models allows the ability to analyze information that considers the specific case at hand. Average computers are able to solve simple FE models in a short amount of time. This attributes to the desirability of developing simple methods for acquiring patient-specific models such as the one presented.
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