Effect of cornea material stiffness on measured intraocular pressure

Intraocular pressure (IOP) in the human eye as measured by a Goldmann applanation tonometer (GAT) is known to be affected by individual differences in central corneal thickness (CCT). However, data from clinical studies also show considerable scatter in the correlation between measured IOP and CCT. One possible implication of the large observed scatter is that the true IOP (IOPT) also depends significantly on individual variations in the material stiffness properties of the cornea. This hypothesis is explored and evaluated herein using computational simulation of applanation tonometry. A simplified 2D finite element model of the eye, which employs a calibrated nonlinear transversely isotropic material model for the cornea, is developed, and a series of GAT simulations is carried out to study the effect of geometry and material properties of the cornea on the IOP readings obtained via GAT. The results of this parametric study provide a simple correction equation, which quantifies the effect on measured IOP of variations in CCT and corneal material stiffness. In addition, several previously proposed IOP correction equations are compared with the one proposed here.