Thickness influence of the multylayer corneal shell on the value of intraocular pressure

A research of changes in the stress-strain state of the corneoscleral shell of the human eye under loading by a flat base stamp is made. In this paper a three-dimentional finite-element model of contact problem under loading of multilayer corneal shell with flat base stamp is presented. This mathematical model is made in software package ANSYS. Cornea is modeled as a transversely isotropic spherical shell of variable thickness composed of four layers: epithelium, Bowman's membrane, stroma of the cornea, and Descement's membrane. Moreover, all layers have individual elastic properties, which are significantly different in tangential direction and in thickness direction. Detailed description of the contact interaction of the corneal shell and flat stamp is presented. Since the thickness of the corneal shell changes in the center, the attached flat stamp deforms the corneal shell in different ways. The paper describes the numerical calculation of the diameter of the contact zone between the shell and the stamp, on the basis of which it is judged in clinical practice about the value of intraocular pressure. Values of correction coefficients of intraocular pressure are obtained depending on the thickness of the corneal shell in its center.