Bahram Notghi 1 Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218 e-mail: notghi@jhu.edu Rajneesh Bhardwaj Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India Shantanu Bailoor Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218 Kimberly A. Thompson Weapons and Materials Research Directorate, Army Research Laboratory, Aberdeen Proving Ground, MD 21005 Ashley A. Weaver VT-WFU Center for Injury Biomechanics, Wake Forest University School of Medicine, Winston-Salem, NC 27101 Joel D. Stitzel VT-WFU Center for Injury Biomechanics, Wake Forest University School of Medicine, Winston-Salem, NC 27101 Thao D. Nguyen Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218 Biomechanical Evaluations of Ocular Injury Risk for Blast Loading Ocular trauma is one of the most common types of combat injuries resulting from the exposure of military personnel with improvised explosive devices. The injury mechanism associated with the primary blast wave is poorly understood. We employed a three- dimensional computational model, which included the main internal ocular structures of the eye, spatially varying thickness of the cornea-scleral shell, and nonlinear tissue prop- erties, to calculate the intraocular pressure and stress state of the eye wall and internal ocular structure caused by the blast. The intraocular pressure and stress magnitudes were applied to estimate the injury risk using existing models for blunt impact and blast loading. The simulation results demonstrated that blast loading can induce significant stresses in the different components of the eyes that correlate with observed primary blast injuries in animal studies. Different injury models produced widely different injury risk predictions, which highlights the need for experimental studies evaluating mechanical and functional damage to the ocular structures caused by the blast loading. [DOI: 10.1115/1.4037072] 1 Introduction The increasing use of explosive weaponry in military conflicts and terrorist attacks has led to an increase in the incidence of combat-related blast injuries sustained by soldiers and civilians. The ratio of ocular traumatic injuries to all injuries during Operation Desert Storm was nearly six times larger than in World War II [1–4] 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 overpres- sure, 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]. Computational modeling studies and animal studies show that the risk of ocular blast injury correlates with the high-pressure shock front, referred to as the positive phase, and the subsequent lower subatmospheric pressure, referred to as the negative phase of the blast wave [8], as well as reflections of the blast wave from the orbit [9] and facial features surrounding the eye [10]. There is, however, a dearth of clinical data that could verify these findings and establish the mechanism of the injury. Measuring and assess- ing the influence of these factors are difficult because survivable primary blast injuries are likely accompanied by injuries from fragments and blunt force trauma and are thus more difficult to distinguish and enumerate. Moreover, the severity of the blast injuries and the distance of the care facility from the injury site mean that often patients are unable to recount the injury event, and witnesses are unavailable. There has been an ongoing effort to identify the mechanism of injuries in recent years. Hines-Beard et al. [11] tested the effects of blast overpressure on mice, by fir- ing short bursts of pressurized air through paintball gun barrels, which inflicted closed-eye injuries with features similar to those seen in patients with ocular blast trauma. Alphonse et al. [12] per- formed an experiment to investigate the effect of low-pressure blasts from fireworks and gunpowder charges on human cadaver eyes. They reported minor corneal abrasion caused by propelled fragmented and found a low risk of severe ocular damage. Sher- wood et al. [13] studied the tissue damage in enucleated porcine eyes caused by a blast wave generated by a shock tube and reported angle recession, internal scleral delamination, cyclodialy- sis, and peripheral chorioretinal detachments. Bhardwaj et al. [10] demonstrated, through a computational modeling study, the strong influence of facial features on blast pressure loading to the eye and the internal ocular structures on the biomechanical response. Due to the importance of the facial feature and the internal ocular structures on the biomechanical response, and challenges to per- forming the experimental studies in full scale, computational modeling can improve the understanding of the mechanism of the primary injuries. Various computational models have been developed to investi- gate the effects of blunt object impact to the eye. Uchio et al. [14] 1 Corresponding author. Manuscript received December 25, 2016; final manuscript received May 20, 2017; published online June 28, 2017. Assoc. Editor: Barclay Morrison. This work is in part a work of the U.S. Government. ASME disclaims all interest in the U.S. Government’s contributions. Journal of Biomechanical Engineering AUGUST 2017, Vol. 139 / 081010-1 Copyright V C 2017 by ASME Downloaded from http://asmedigitalcollection.asme.org/biomechanical/article-pdf/139/8/081010/5987995/bio_139_08_081010.pdf by guest on 28 November 2021