Blast-related ocular trauma comprises a specialized subgroup blast injuries which cause penetrating and blunt force injuries to the eye and its structure. The incidence of ocular trauma due to blast forces has increased dramatically with the introduction of new explosives technology into modern warfare. The availability of these volatile materials, coupled with the tactics of contemporary terrorism, has caused a rise in the number of homemade bombs capable of extreme physical harm.
Military classification of improvised explosive devices
The United States Department of Defense classifies IEDs as explosive machines that are constructed exclusively (i.e., without mass production) and result in the direct physical harm of surrounding individuals. The use of these bombs by insurgents has been the number one cause of death and injury among Coalition soldiers since the start of Operation Iraqi Freedom in April 2003. Detonation of the IED occurs remotely or as victim-induced mechanical disturbance. Further classification of IEDs falls under the mechanism of delivery – vehicle-based, boat-borne, animal-borne, suicide bomber – and the resultant effect upon detonation: Explosive: Bombs of this nature incorporate chemicals and substances that result in the formation of a large blast; may incorporate pyrotechnics. Often employs shrapnel to inflict harm by mechanical trauma. Incendiary: utilize highly exothermic chemical processes to initiate the rapid spread of fire and pyrotechnic damage Chemical: Bombs in this class include noxious chemical materials that may cause a patho-physiological response in individuals exposed to the blast area during and post-explosion. Biological: Much like the chemical-type, with the exception that biological bombs use vector-borne pathogens or other biohazardous materials to initiate a patho-physiological response in exposed individuals.
Explosion physics
The discharge of a bomb is characterized by the near-instantaneous sublimation of solids or rapid vaporization of liquids into the gas phase. The amount of explosive materials used, the concentration and identity of secondary materials incorporated into bomb design, and the location and height of bomb placement all determine the magnitude of the explosion. The gas formed displaces the surrounding medium – usually air – and causes a dramatic increase in pressure that forms a characteristic blast wave, often referred to as the leading shock wave. Physically, this wave is characterized as a non-linear, discontinuous wave front that features infinite amplitude and accompanying acoustic pressure wave that may generate a pressure as high as 100MPa in a time as short as one microsecond. This peak pressure, or blast overpressure point, generates a positive pressure during blast wave propagation and results in the dispersal of positive pressure across the blast radius. This positive pressure phase is immediately followed by a period of negative pressure relative to pre-blast conditions; this phase may also account for injuries sustained during a blast.
Impact of explosion upon individuals in the blast radius
The prevalence of mines in Operation Iraqi Freedom and Operation Enduring Freedom has made them the most frequent mechanism of injury behind the traumatic “signature” in modern warfare, blast-induced traumatic brain injury (bTBI). Whereas body armor has lowered the incidence of death due to collapse of gas-filled organs (the most frequent cause of blast-related deaths prior to Operation Desert Storm) healthcare providers must now develop methods for treating bTBI. Despite their frequency on the warfront, the home-produced nature of these mines makes classifying patient presentations difficult for military healthcare providers. The majority of lethal bTBIs reveal axonal shearing as the mechanism of fatality, with the greatest amount of nerve fiber and vascular shearing occurring in the frontal and temporal lobes.