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

Abstract

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 þ0.25 and À1.4 MegaPascal (MPa) for tympanic rupture, þ3 and À1 MPa for lung damage, and þ20 and À6 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 À1 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. (Invest Ophthalmol Vis Sci. 2012;53:8057-8066) DOI:10.1167/iovs.12-10591 P rimary blast injury (PBI) refers to biological damage caused by the peak incident overpressure (PIO) wave generated by an explosion. Initially described exclusively in hollow, air-filled organs, 1,2 the spectrum of PBI progressively enlarged to encompass fluid-filled organs, including the central nervous system 3,4 and the eye. 3-6Macular holes, choroidal rupture, and optic nerve damage occur relatively frequently after blunt trauma, 7 and although the pathogenic mechanism remains unclear, vitreous traction, 8 globe deformation, differential eye layer stiffness, 9 shockwave propagation, and multiaxial strain 10 likely participate.Finite element modeling (FEM) is a numerical analysis method largely used to simulate multiphysics problems. Previous applications to ophthalmology [11][12][13] and, specifically, to blunt eye trauma 10 have been reported. The purpose of the present paper is to create a computational model of ocular PBI, simulate the propagation of blast waves through the orbit, and explain its pathogenesis. The study was prompted by the observation of macular holes, multiple choroidal ruptures, subretinal bleeding, and optic atrophy after blast exposure, in the absence of any contact with splinters and/or flying objects (Fig. 1). MATERIALS AND METHODS Finite Element ModelingThe eye model has been previously described, 10,14 while orbit and retrobulbar fat tissue were reconstructed based on patient computed tomography scan and magnetic resonance imaging ( Fig. 2; see the Appendix for further technical details on FEM). C...

Assessment of the Effectiveness of Combat Eyewear Protection Against Blast Overpressure

“…These results suggest that a blast wave can potentially cause eye injury in humans as well. Indeed, recent finite element (FE) studies have investigated the potential causes of primaryblast-induced eye injury, suggesting different mechanisms of injury without providing, difficult-to-obtain, supporting experimental evidence [9,10].…”

Biomechanical Evaluations of Ocular Injury Risk for Blast Loading

“…The ratio of ocular traumatic injuries to all injuries during Operation Desert Storm was nearly six times larger than in World War II [1][2][3][4] and made ocular trauma the fourth most common injury related to military deployment [5]. Blast injuries can be separated into four categories: primary from the blast overpressure, secondary from propelled fragments, tertiary from blunt impact, and quaternary from burns and other effects [6]. While secondary, tertiary, and quaternary injury mechanisms can be identified within the military's casualty care system, mechanisms unique to primary blast injuries are still poorly understood [7].…”

“…Stitzel and coworker [19,20] developed a model to study the effect of blast loading on the human eye, which used the pressure on the eye obtained as a function of the mass of trinitrotoluene (TNT) charge and its distance from the subject. Rossi et al [6] investigated the dynamic response of the eye to blast overpressure and predicted damage to the macula and optic nerve head caused by the development of standing wave inside the globe. Esposito et al [21] investigated the effects of the peak overpressure and blast duration on stresses at the macula.…”

Effects of repetitive low-level blast exposure on visual system and ocular structures

“…The primary blast shock wave can propagate through the different media of the eye globe and related orbital anatomical structures causing contusion to organs and tissue in the region [3][4]. Such ocular damage resulting from primary blast was initially described by Duke-Elder, and included subconjunctival hemorrhages, traumatic cataract, traumatic uveitis, secondary glaucoma, retinal edema, choroidal rupture, and macular lesions [5].…”

“…Finally, computational models using finite element modeling have been characterized to simulate the propagation of blast waves through the orbit and attempt to explain the damage induced by the primary blast per se without the secondary or tertiary injury cofounder [3][4].…”