Determining the probability of ocular trauma from survivable primary blast

Ocular injuries make up a significant portion of battlefield injuries. Primary blast refers to the shock-wave generated by the explosive device itself and is characterized by a Friedlander pressure-time history. The connection between primary blast and the occurrence of ocular trauma has largely remained uncertain. Shock-tubes precisely generate shocks described by a Friedlander pressure-time history, where the pressure of a gas rises nearly instantaneously from an ambient to a maximal level, and then returns to the ambient pressure. Porcine eyes were placed within orbit-mimics and treated with primary blast from a shock-tube. All eyes were scanned before and after treatment with shock via B-mode ultrasound and ultrasound biomicroscopy (UBM) then processed for histological evaluation. Ordinal logistic regression was used for the analysis of the resulting data, using the treatment methods and blast parameters as predictors and the injury scores as the levels of the response. Examination of the ex vivo porcine eyes showed that the eyes suffered retinal detachments, chorio-retinal tears, de-lamination of the layers of the scleral tissue, and striations of the nerve fibers of the optic nerve head. The results of the ordinal logistic regression showed that several key blast parameters were linked with the probability of obtaining specific injury grades. Confounding factors such as the mass of the eye and the induced IOP were also implicated in determining the injury grades. The results indicate that the magnitude of primary blast is sufficient to cause severe injuries to multiple tissue types and structures of the eye, and should be considered a serious risk factor independent of secondary blast, especially because current military eyewear is not designed to protect against the high overpressures generated by a primary blast.