Primary Blast Injury to the Eye and Orbit: Finite Element Modeling

Primary Blast Injury (PBI) mostly affects air-filled organs although sporadically reported in fluid-filled organs including the eye. Purpose of present paper is to explain orbit blast injury mechanisms through Finite Element Modelling (FEM). Design: FEM mesh of eye, orbit and skull was 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% mortality chances. Results: Pressures within the orbit ranged between +0.25 and -1.4 MegaPascal (MPa) for TR, +3 and -1 MPa for LD and +20 and -6 MPa for 50M. Higher trinitrotoluene (TNT) quantity and closer explosion caused significantly higher pressures and 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 sec -1 at all locations even for the least amount of TNT. Conclusion: Orbit pyramid-like shape with bony walls and the mechanical impedance mismatch between fluid-like 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.