Optically inspired biomechanical model of the human eyeball

Abstract

Currently available biomechanical models of the human eyeball focus mainly on the geometries and material properties of its components while little attention has been given to its optics--the eye's primary function. We postulate that in the evolution process, the mechanical structure of the eyeball has been influenced by its optical functions. We develop a numerical finite element analysis-based model in which the eyeball geometry and its material properties are linked to the optical functions of the eye. This is achieved by controlling in the model all essential optical functions while still choosing material properties from a range of clinically available data. In particular, it is assumed that in a certain range of intraocular pressures, the eye is able to maintain focus. This so-called property of optical self-adjustments provides a more constrained set of numerical solutions in which the number of free model parameters significantly decreases, leading to models that are more robust. Further, we investigate two specific cases of a model that satisfies optical self-adjustment: (1) a full model in which the cornea is flexibly attached to sclera at the limbus, and (2) a fixed cornea model in which the cornea is not allowed to move at the limbus. We conclude that for a biomechanical model of the eyeball to mimic the optical function of a real eye, it is crucial that the cornea is allowed to move at the limbal junction, that the materials used for the cornea and sclera are strongly nonlinear, and that their moduli of elasticity remain in a very close relationship.

Material properties of the cornea and sclera: A modelling approach to test experimental analysis

“…A finite element model based on previous models for the human eye (Srodka and Iskander, 2008;Srodka and Pierscionek, 2008) but using biometric parameters obtained from the porcine eyeball was created (Fig. 1).…”

Biomechanical and optical behavior of human corneas before and after photorefractive keratectomy

“…If individual in vivo tests are missing, help in the choice of the material properties can be sought by considering the inevitable link between mechanics and optics. 20,22,27 The aim of the present study was to assess the ability of an improved patient-specific version of a finiteelement code 4,20 in predicting the optical and biomechanical outcomes of RK, in particular the corrected refractive power and the postoperative stress distribution in the treated corneas. The current version of the finite-element code includes a procedure that replicates the typical corneal ablation in PRK 20 and uses improved models of statistically distributed fiber materials.…”

Corneal Biomechanical Changes after Collagen Cross-Linking from Porcine Eye Inflation Experiments

“…In the whole eye model, the limbal junction is allowed to move, which is thought to be crucial to establish a biomechanical model mimicking the optical function of a real eye. 18,[23][24][25] Porcine models are frequently used to assess biomechanical properties that may be extrapolated to human corneas. Despite differences in corneal thickness (the average porcine cornea is 1.6ϫ thicker than the human cornea) and stiffness (the porcine cornea is more elastic than the human cornea), 26,27 it is accepted that the porcine cornea is a suitable model for the human cornea in mechanical properties.…”