The mechanical properties of the rabbit and human cornea.

The extensibility of rabbit and human corneas was measured by raising the pressure within the intact globe of the eye and measuring the displacements of two very small mercury drops on the corneal surface. The human cornea showed a negligible extensibility under low stresses. The rabbit tissue, however, underwent a 9% strain under low pressures with a curvilinear relationship between stress and strain. At higher pressures the relationship was linear, and the tissue showed some creep. The low pressure stress-strain relationship of the rabbit could not be explained on the basis that the collagen fibrils were being straightened out from an initial set in a sinusoidal wave. When the stroma was isolated from Descemet's membrane, it showed a negligible low pressure extensibility in rabbit and man. On the other hand, isolated Descemet's membrane was very extensible in both species. The difference between them in the behavior of the intact cornea seems to lie in the relative initial strain in the stroma and Descemet's membrane.