A finite element approach to predicting scleral response to mechanical stress.

The technique of finite element analysis was applied to ocular geometry to predict the effects of mechanical loads, such as those imposed by glaucoma shunt implants, on the stress distribution and organization of the collagen fiber matrix that comprises the sclera. Axisymmetric and 2D shell models of the sclera were constructed to simulate the application of a pressure region on the exterior surface of the sclera. Both models predict redistribution of stress from the center of the pressure region to its outer edge where the magnitude of principal stresses exceeds that of any other location in the models. The models are supported by morphological changes in tissue samples from human and rabbit eyes that have been subjected to stresses similar to those depicted in the models. Analysis of scleral collagen using polarized light shows the tissue is highly organized and responsive: Collagen aligns itself along the principal stresses within the sclera. Furthermore, amount of choroidal hemorrhaging commonly associated with glaucoma shunts correlates with redistribution of mechanical stress, suggesting that pressure imposed by plate rather than reduction of intraocular pressure is responsible for hemorrhage.