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W. J. Dupps, Jr., A. Sinha Roy; The Effect of Varied Corneal Stiffness on the Corneal Biomechanical Response to LASIK in a Whole-Eye Finite Element Model. Invest. Ophthalmol. Vis. Sci. 2008;49(13):670. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the sensitivity of LASIK-mediated corneal refractive power changes to elasticity variations in a whole-eye finite element model.
Using geometry derived from magnetic resonance images of a human eye, a finite element based whole-eye model was constructed. The cornea was modeled as a nonlinear hyperelastic, incompressible material. The whole-eye model was parameterized to study the effect of variations in corneal elasticity on the corneal optical response to intraocular pressure (IOP) changes and LASIK for myopia with attempted corrections of 2, 4 or 6 diopters. Two different sets of experimentally derived corneal hyperelastic parameters were used, while scleral and other extracorneal material properties were held constant.
In the whole-eye model, simulated myopic LASIK caused central flattening and peripheral steepening in low-stiffness and high-stiffness corneas. In contrast to an otherwise comparable cornea-only model incapable of limbal motion, a whole-eye model with low corneal stiffness demonstrated greater stresses and displacements in the paracentral cornea than in the limbus and central cornea and predicted undercorrection of myopia. With high corneal stiffness, maximum displacements shifted away from the paracentral cornea toward the limbus, favoring additional mechanically mediated central flattening and refractive overcorrection (hyperopia). These divergent trends were accentuated by increases in IOP after LASIK.
In a whole-eye model without a fixed-limbus boundary condition, corneal biomechanical and optical behaviors depend upon the cornea’s elasticity and its relationship to extracorneal structures. The simulation suggests that patient-to-patient variations in the corneo-scleral stiffness relationship, whether arising from disease, surgery or photochemical modification of elasticity, can affect steady-state corneal shape, refractive outcomes after LASIK, and the refractive response to pressure perturbations.
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