"Biomechanics of Primary Blast Injury to the Human Eye"

Vicky Nguyen, Ph.D.
Whiting School of Engineering
Johns Hopkins University

Primary blast injury is caused by the impact and propagation of the blast wave through the body producing damage to the internal organs and tissues. The incidence and severity of primary blast injuries have increased because of the increasing use and effectiveness of explosive weapons in military operations and terrorist attacks. In Operation Iraqi Freedom and Operation Enduring Freedom, blast from munitions and IDEs were responsible for 80% of ocular injuries [1,2].  Studies have shown that the majority of blast injuries to the eye are caused by high-velocity fragments and by blunt force trauma from being hit by large propelled objects or from being thrown by the blast wave [1,2]. Current protective eye equipment, which includes spectacles and goggles, made from transparent ballistic materials, are designed to protect mainly against high velocity projectiles.  The blast wave is also thought to contribute significantly to blast injuries to the eye. However, the mechanisms and risk factors of primary blast injuries to the eye remain poorly understood. Also poorly understood is the effectiveness the current eye armor in mitigating primary blast injuries.  This is because primary blast injuries to the eye rarely occur in isolation and are difficult to separate from injuries caused by blunt force trauma and penetrating fragments.  Moreover, experiments in animal models are limited because the dynamics of the blast wave are strongly influenced by facial structures, which are inherently different in animal models than in humans
In this presentation, she will describe their efforts to develop a computational approach to investigate the biomechanics of primary blast injury to the eye. They have developed a fluid-structure interaction method that solves for the development of the blast wave, deformation of the soft tissues of the eye, and the energy transfer between the fluid and solid mediums.  They applied the model to evaluate the blast pressure loading to the face of a representative 21 year-old male from different blast angles and locations. Results showed that the blast wave focused on the eye, generating the highest pressure loading on the face, because of reflections from surrounding facial features. The blast loading on the eye was asymmetrical, which caused large shear stresses on the sclera where it attaches to the extra-orbital tissues. Blast wave propagation through the eye resulted in the highest tensile stresses at the macula and optic nerve head.   They next evaluated the effectiveness of spectacles and goggles in mitigating the pressure loading on the eye. Their results corroborated free field blast experimental measurements showing that the goggles were more effective than spectacles in reducing the peak blast pressure loading on the eye. However, the goggles trapped the blast wave in a small region in the front of the eye and produced a sustained higher pressure loading after the passing of the blast wave.  These findings identify vulnerable locations in the eye to direct experimental studies of blast injuries and guide the design of new eye amor.   
1.Weichel ED, Colyer MH, Ludlow SE, Bower KS, Eiseman AS. Ophthalmology 2008;115:2235-2245.
2.Mader TH, Carroll RD, Clifton SS, George RK, Ritchey P, Neville P. Ophthalmology 2006;113:97-104.
3.Ritenour AE, Toney WB. Primary blast injury: Update on diagnosis and treatment. Crit. Care. Med. 2008. 36:S311-S317.