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Scott Lovald, Andrew Rau, Steven Nissman, Nicoli Ames, John McNulty, Jorge Ochoa, Michael Baldwinson; Finite Element Analysis of Penetrating Injury to the Human Eye. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2399.
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© ARVO (1962-2015); The Authors (2016-present)
Penetrating injuries to the eye are among the most frequent causes of permanent visual impairment. The purpose of this study was to determine the strain at which rupture occurs in the cornea due to a penetrating object.
For the experiment, probes of varying diameters (1.0, 1.5, and 2.0 mm) were pressed into the apex of the cornea in 36 human cadaveric globes until perforation of the specimen. To match the experiment, an axisymmetric finite element model of the idealized human globe was created in Abaqus 6.14 (Figure 1). The cornea and sclera were modeled as isotropic nonlinear hyperelastic materials. To evaluate model sensitivity, three separate models for the sclera were constructed (minimum, medium, and maximum stiffness) within the range of experimentally-observed material behavior. In addition, two separate internal pressure conditions were implemented: 1) a sealed fluid cavity with an initial pressure, and 2) a constant pressure applied directly to the cavity surfaces. The model was 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 30.5±5.5 N (1.0 mm probe) to 40.5±8.3 N (1.5 mm probe) to 58.2±14.5 N (2.0 mm probe) as the probe size increased (p<0.002). The force-displacement responses of the finite element models of all three probe sizes bounded and tracked the experimental data. The peak strain at failure in the cornea was located on its posterior surface. This strain was in the range of 29% to 33% for all models analyzed. Figure 2 shows strain contours for the 1 mm probe.
The current study has developed a validated finite element model of the human eye for analysis of penetrating injury to the cornea. The results have determined an objective failure strain of corneal tissue, which is consistent between sensitivity studies of varying material models, pressure conditions, and penetrating objects sizes. These results provide critical, quantitative information for understanding the risk of penetrating eye injuries.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Finite element model set-up for globe indentation. Material sections are indicated in the middle image. The figure on the right shows the indenter probe displaced into the cornea.
The maximum principal strain in the cornea is shown for each 1.0 mm probe analysis at the step corresponding to the average experimental failure force.
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