Corneal Stress Distribution Using the Procedure of Goldmann Applanation Tonometry, as Tested on a Human Cornea Model.

Abstract

Objective: To assess the effect of corneal thinning and changes in intraocular pressure (IOP) on the distribution of corneal stress induced by Goldmann applanation tonometry (GAT).

Methods: A 2D model of a human cornea was created using a computer-aided design and finite element analysis software, employing previously reported corneal biomechanical properties. The GAT procedure was simulated, and the magnitude and distribution of stress in the corneal stroma were obtained for several corneal thicknesses, stiffnesses, and IOP.

Results: A significant increase in stress was found in the outer and inner layers of the central cornea and in the inner layers of the surrounding central region. The maximal stress value was observed in the central outer layers when the stiffness was doubled, as in our theoretical baseline cornea (125.16 kPa). Minimal stress was observed in the central inner layers for a central corneal thickness of 300 µm (28.17 kPa). The thickness and stiffness of the cornea significantly influenced the magnitude of the stress, whereas the stress distribution in the cornea did not show significant changes. The change in IOP did not induce significant changes in either stress magnitude or stress distribution.

Conclusions: The changes and distribution of corneal stress when a GAT procedure is performed support the idea that variations in corneal thickness and stiffness induce changes in corneal biomechanics that may be relevant for IOP readings. These findings are relevant for assessing IOP in corneas that have undergone surgical procedures or have diseases that alter their layers.