Finite element analysis and experimental evaluation of penetrating injury through the cornea

Penetration injuries of the eye are among the most frequent causes of permanent visual impairment resulting from trauma. The purpose of this study was to determine the peak strain at which rupture occurs in the cornea due to a penetrating object. Probes of varying diameters (1.0, 1.5, and 2.0mm) were pressed into the apex of the cornea of 36 human cadaveric eye specimens until perforation or rupture of the specimen at the cornea, limbus, or sclera occurred. An axisymmetric finite element model of the human globe was created to replicate the experimental set-up. The models were used to map the force-displacement response of the experiments and quantitatively determine a peak strain at which the eye ruptures. For the experiments, the average force at failure increased from the smallest to largest probe (p<0.002). The average forces at failure are as follows: 30.5±5.5N (1.0mm probe); 40.5±8.3N (1.5mm probe); 58.2±14.5N (2.0mm probe). The force-displacement responses of the finite element models of all three probe sizes bounded and tracked the experimental data. In all cases, the peak strain at failure in the cornea was located on the posterior surface of the cornea, directly adjacent to the corneal apex. This strain was in the range of 29% to 33% for all models analyzed. In addition to determining an objective failure strain of corneal tissue, the model developed in this study can provide quantitative information for understanding the risk of penetrating eye injuries.