Abstract
Purpose: The geometries used to conduct numerical simulations of the biomechanics of the human cornea are reconstructed from images of the physiological configuration of the system, which is not in a stress-free state because of the interaction with the surrounding tissues. If the goal of the simulation is a realistic estimation of the mechanical engagement of the system, it is mandatory to obtain a stress-free configuration to which the external actions can be applied.
 Methods: Starting from a unique physiological image, the search of the stress-free configuration must be based on methods of inverse analysis. Inverse analysis assumes the knowledge of one or more geometrical configurations and, chosen a material model, obtains the optimal values of the material parameters that provide the numerical configurations closest to the physiological images. Given the multiplicity of available material models, the solution is not unique.
 Results: Three exemplary material models are used in this study to demonstrate that the obtained, non-unique, stress-free configuration is indeed strongly dependent on both material model and on material parameters.
 Conclusion: The likeliness of recovering the actual stress-free configuration of the human cornea can be improved by using and comparing two or more imaged configurations of the same cornea.
Highlights
Among all the so biological tissues of the human body, the cornea is unique because of the transparency and the accessibility of its location
We describe the approach for the simultaneous identification of the natural configuration and a limited number of material properties of the adopted material models, present the results obtained on the set of patient specific corneas, and discuss the numerical findings in view of possible applications
Having chosen a material model and a set of material parameters, a numerical analysis where the posterior surface of the cornea is pressurized with the physiological intraocular pressure (IOP) will provide, as solution, the displacement field associated to the stresses that balance the IOP by means of the material model
Summary
Among all the so biological tissues of the human body, the cornea is unique because of the transparency and the accessibility of its location. These features make the cornea one of the most deeply studied and better known biological materials, since advanced optical imaging has revealed all the details of the underlying microstructure. Spectacles and contact lenses have been and are largely used, but in the last two decades laser technology has allowed to correct refraction errors permanently by modifying the refractive power of cornea, in consideration of the accessibility of the organ. For non-standard corneas that must undergo refractive surgery, the support of a numerical model of the cornea with patient-specific features may become of great importance to reduce the possibility of mistakes and to help in the selection and design of the optimal treatment
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