Numerical modeling of paintball impact ocular trauma: identification of progressive injury mechanisms.

PURPOSE To create a computer-based numerical simulation model for comparison with empiric paintball-ocular ballistic study findings, allowing identification of the dynamic physical mechanisms (stress, strain, pressure) responsible for intraocular traumatic injury accompanying blunt ocular impact. Virtual experiments with numerical models could exploit mathematical "instrumentation" to facilitate internal observation impossible with physical experiments alone. METHODS Models of human eye structures and orbit were implemented into the finite-volume Eulerian numerical hydrocode CTH. Numerical simulation results were compared with dynamic imaging and postimpact histopathology obtained during previous ballistic impact experiments on fresh porcine eyes impacted with paintballs. Forty numerical simulations and 59 impact experiments were conducted as part of the study. RESULTS Time-lapse correlations showed the CTH models to be dynamically commensurate with orbital penetration and globe deformation measured from ballistic high-speed videos. CTH also predicted the types and levels of damage observed in detailed postimpact pathologic assessments of porcine specimens. High strain in the ciliary body and zonule corresponded with angle recession and lens displacement pathologically. Globe rupture was attained at the highest paintball impact velocities in both the porcine ballistic studies and CTH models, consistent with predicted dynamic intraocular pressures. The simulations also revealed that phenomena such as macular Berlin's edema, midperipheral retinoschisis, and choroidal and retinal detachment might be explained by focal dynamic pressure-wave reflection from the interior surface of the globe. CONCLUSIONS Significant insight was gained regarding the physical mechanisms responsible for injury. CTH predictions corresponded closely with previous ballistic experimental results, adding intraocular detail otherwise unattainable.