A nonlinear finite element model of the eye with experimental validation for the prediction of globe rupture

Over 2.4 million eye injuries occur each year in the US, with over 30,000 patients left blind as a result of the trauma. The majority of these injuries occur in automobile crashes, military operations and sporting activities. This paper presents a nonlinear finite element model of the eye and the results of 22 experiments using human eyes to validate for globe rupture injury prediction. The model of the human eye consists of the cornea, sclera, lens, ciliary body, zonules, aqueous humor and vitreous body. Lagrangian membrane elements are used for the cornea and sclera, Lagrangian bricks for the lens, ciliary, and zonules, and Eulerian brick elements comprise the aqueous and vitreous. Nonlinear, isotropic material properties of the sclera and cornea were gathered from uniaxial tensile strip tests performed up to rupture. Dynamic modeling was performed using LS-Dyna. Experimental validation tests consisted of 22 tests using three scenarios: impacts from foam particles, BB's, and baseballs onto fresh eyes used within 24 hours postmortem. The energies of the projectiles were chosen so as to provide both globe rupture and no rupture tests. Displacements of the eye were recorded using high speed color video at 7100 frames per second. The matched simulations predicted rupture of the eye when rupture was seen in the BB and baseball tests, and closely predicted displacements of the eye for the foam tests. Globe rupture has previously been shown to occur at peak stresses of 9.4 MPa using the material properties included in the model. Because of dynamic effects and improvements in boundary conditions resulting from a more realistic modeling of the fluid in the anterior and posterior chambers, the stresses can be much higher than those previously predicted, with the globe remaining intact. The model is empirically verified to predict globe rupture for stresses in the corneoscleral shell exceeding 23 MPa, and local dynamic pressures exceeding 2.1 MPa. The model can be used as a predictive aid to reduce the burden of eye injury, and can serve as a validated model to predict globe rupture.