Importance of preparation and mounting in determining the dynamic mechanical response of the porcine eye to blunt impact

The ex vivo porcine eye is routinely used as a proxy for the human eye in trauma experiments. The eye is generally potted in 10% gelatin mold to simulate the mechanical response of orbital cavity contents. Then, the gelatin is cast in a rigid container intended to replicate the orbital bones surrounding the eye. The purpose of this study was to determine the accuracy of this model in recapitulating the in vivo human eye response in ocular trauma/impact research. The mechanical properties of the porcine eye were characterized in dynamic impact and quasi-static loading to determine whether the potting method influenced the overall response of the eye model. Three different eye setups included a bare, 3.6% gelatin mounting, and 10% mounting were involved in dynamic impact and quasi-static loading. Four gelatin concentrations of 3.6%, 5.2%, 6.8%, and 10% were also mechanically tested using dynamic shear rheology and quasi-static uniaxial compression. The porcine eye demonstrated differences on stiffness between dynamic impact and quasi-static loading. Eyes loaded dynamically were significantly stiffer than those loaded quasi-statically, regardless of the potting procedure. Eyes potted in 3.6% gelatin was less stiff than those mounted in 10% gelatin at low displacements but became increasingly stiff as displacement increased during dynamic loading. The bare eyes were far stiffer at low displacements and gradually became less stiff. The mechanisms of ocular deformation in the quasi-static and dynamic loading cases were considerably different among the three potting techniques. The mechanical testing of the gelatin showed the significant incremental trend of stiffness as the concentration increased. These results were used to estimate the optimal concentration which would mimic the in vivo human orbital fat and connective tissue properties.