Finite element simulation of Goldmann tonometry after refractive surgery.

Abstract

The problem of accuracy of intraocular pressure (IOP) measurement using Goldmann Applanation Tonometry (GAT) after a refractive surgery is still unresolved. In this study a numerical simulation of refractive surgery and GAT is proposed as a method to evaluate accuracy of the correction formula for GAT reading after changes in corneal curvature and thickness. In the finite element analysis the effect of the corneal shell buckling was taken into account. This effect is responsible for the nonlinear relation of Goldmann applanation tonometer measurement and intraocular pressure. Goldmann applanation tonometry was simulated for different ablation depths and values of intraocular pressure levels. The results of the simulation indicate a strong relation between the Goldmann applanation reading and the intraocular pressure level for values greater than nominal (about 16 mmHg). The estimation error of the intraocular pressure after changes in corneal geometry, is lower than 1 mmHg for IOP = 32 mmHg and lower than 3 mmHg for IOP = 48 mmHg. The proposed correction formula of Goldmann applanation tonometry occurred to be useful in the cases after the corneal refractive surgery regardless of the intraocular pressure values and ablation depth.