Firecracker eye exposure: experimental study and simulation.

Understanding the mechanisms of traumatic ocular injury is helpful to make accurate diagnoses before the symptoms emerge and to develop specific eye protection. The comprehension of the dynamics of primary blast injury mechanisms is a challenging issue. The question is whether the pressure wave propagation and reflection alone could cause ocular damage. To date, there are dissenting opinions and no conclusive evidence thereupon. A previous numerical investigation of blast trauma highlighted the dynamic effect of pressure propagation and its amplification by the geometry of the bony orbit, inducing a resonance cavity effect and a standing wave hazardous for eye tissues. The objective of the current work is to find experimental evidence of the numerically identified phenomenon. Therefore, tests aimed at evaluating the response of porcine eyes to blast overpressure generated by firecrackers explosion were performed. The orbital cavity effect was considered mounting the enucleated eyes inside a dummy orbit. The experimental measurements obtained during the explosion tests presented in this paper corroborate the numerical evidence of a high-frequency pressure amplification, enhancing the loading on the ocular tissues, attributable to the orbital bony walls surrounding the eye.

Primary blast injury to the eye and orbit: finite element modeling.

PURPOSE: Primary blast injury (PBI) mostly affects air-filled organs, although it is sporadically reported in fluid-filled organs, including the eye. The purpose of the present paper is to explain orbit blast injury mechanisms through finite element modeling (FEM). METHODS: FEM meshes of the eye, orbit, and skull were generated. Pressure, strain, and strain rates were calculated at the cornea, vitreous base, equator, macula, and orbit apex for pressures known to cause tympanic rupture, lung damage, and 50% chance of mortality. RESULTS: Pressures within the orbit ranged between +0.25 and -1.4 MegaPascal (MPa) for tympanic rupture, +3 and -1 MPa for lung damage, and +20 and -6 MPa for 50% mortality. Higher trinitrotoluene (TNT) quantity and closer explosion caused significantly higher pressures, and the impact angle significantly influenced pressure at all locations. Pressure waves reflected and amplified to create steady waves resonating within the orbit. Strain reached 20% along multiple axes, and strain rates exceeded 30,000 s(-1) at all locations even for the smallest amount of TNT. CONCLUSIONS: The orbit's pyramidlike shape with bony walls and the mechanical impedance mismatch between fluidlike content and anterior air-tissue interface determine pressure wave reflection and amplification. The resulting steady wave resonates within the orbit and can explain both macular holes and optic nerve damage after ocular PBI.