A finite element model of the cornea has been constructed on the basis of the mechanical properties of its ultrastructural elements which predicts the outcome of radial keratotomy operations in a satisfactory manner. The objective of this proposal is to refine and critically test the model. These refinements will include the nonlinearity of the stress-strain relationship of the collagen fibrils and will account for the shear stiffness of the ground substance that will allow the transmission of tensile forces from one fibril to its neighbors. The shift in fluid within the tissue that occurs when it is distorted will also be allowed for. These mechanical properties will be measured in isolated tissue and introduced into the model. The model will be verified by measuring the distortion of human corneas by measuring their contours photographically and by interference holography. Distortions will be effected by raising the intraocular pressure, indenting or applanating the cornea under a load and by creating a localized thinning of the stroma by evaporation or pressure. The same tests will be carried out on eyes that have undergone keratoplasty and the results compared with the predictions of the model.
