Finite element modeling of corneal biomechanical behavior

To optimize the construction details of corneal numerical models while maintaining efficiency and reliability of predictions.

Nonlinear finite element analysis of corneal models was carried out to assess the importance of considering the cornea's hyperelastic, hysteretic and anisotropic behavior, multi-layer construction, weak inter-lamellar adhesion, non-uniform thickness, elliptical topography, and connection to the sclera. The effect of each of these parameters was determined by removing it from the numerical models and assessing the effect on the results. This exercise was carried out under two load cases--a uniform posterior pressure subjecting the cornea to predominantly membrane tension stresses, and a concentrated anterior pressure as applied by the Ocular Response Analyzer (Reichert Ophthalmic Instruments), which creates mainly bending stresses.

Corneal models subjected to mainly bending stresses were particularly sensitive to simplifications in modeling corneal nonuniform thickness, weak interlamellar adhesion, and multi-layer construction. On the other hand, models under mainly membrane tension were more sensitive to simplifications in elliptical profile and connection to the sclera. Considering hyper-elasticity was important in both cases. Hysteresis was also important, but only in applications involving load reversal.

Although simplifications may be necessary to reduce the cost of numerical model construction and analysis, the selection of which simplifications to adopt should be done with care. They should only be considered when their effect on results is acceptably small, and their inclusion does not make the model significantly different from real-life conditions.