Assessment of Corneal Biomechanical Behavior Under Posterior and Anterior Pressure

PURPOSE: To determine the biomechanical response of the rabbit cornea to inflation under posterior and anterior pressure. METHODS: Twelve Japanese white rabbits were included in the study. A randomly selected eye from each animal was subjected to posterior pressure in an inflation test rig, and the other eye was subjected to anterior pressure after manually reversing its curvature. Specimens were loaded by cycles of pressure up to 40 mmHg, and the experimentally obtained pressure-deformation data were used to derive the stress–strain behavior of each eye using an inverse modeling procedure. RESULTS: The differences between the two groups in corneal thickness, diameter, and intraocular pressure (IOP) were not statistically significant ( P =.935, .879 and .368, respectively). Corneas tested under posterior pressure displayed significantly higher stiffness (as measured by the tangent modulus) than those inflated by anterior pressure ( P< .001). CONCLUSIONS: Cornea is a nonlinear viscoelastic tissue that presents different mechanical properties when tested under posterior and anterior pressure. The determination of the behavior under both forms of pressure could contribute to the construction of accurate finite element simulations of corneal behavior and the correction of tonometric IOP measurements. The difference in mechanical behavior between anteriorly and posteriorly loaded corneas in the study, although significant, could have been partly affected by the changes in microstructure possibly caused by changing corneal form to enable anterior loading.