TUESDAY, July 3, 2012 (MedPage Today) — Injuries to the eye caused by fireworks mostly involve the cornea and do not appear to be associated with blast pressures, but rather result from detritus projected into the eye, a simulated experiment found.
The risk of injuries such as globe rupture and damage to the lens or retina was no greater than 0.01 percent in cadaver eyes exposed to controlled blast pressures, according to Stefan M. Duma, PhD, of Virginia Tech-Wake Forest University in Blacksburg, Va., and colleagues.
Rather, the only injuries observed were small abrasions of the cornea with patterns suggesting they were caused by projected explosive remnants, Duma's group reported in a research letter in the July 4 issue of the Journal of the American Medical Association.
Some 2,000 cases of eye injury occur each year from accidents with fireworks, primarily among youth. It has not been determined, however, whether injuries such as bleeding into the sclera or rupture of the globe result from blast overpressures, or whether ocular damage results from projected remnants of the fireworks entering the eye.
To clarify this, the researchers obtained cadaver eyes that were pressurized to normal intraocular pressures of 14.95 mm Hg using Ringer's lactate, and exposed them to 10-g charges of gunpowder at distances of 22 cm, 12 cm, and 7 cm.
One pressure sensor was inserted into the vitreous area of the eye, and four additional sensors surrounding the eye measured total pressure, static pressure, and wave velocity.
The gunpowder charges also were compared with the total and static pressures and wave velocities caused by actual firecracker explosions. For those explosions, three commercial firecrackers were tested without an eye to obtain measurements of total pressure, static pressure, and wave velocity.
Intraocular pressures resulting from the gunpowder charges were then used for calculating risks of injuries such as anterior bleeding and damage to the lens and retina. These calculations were based on risk curves previously developed by Duma and colleagues from animal tests.
Not only did the intraocular pressures increase the closer the eye was to the explosion, but intraocular pressures also showed a linear correlation with total pressures, the researchers explained.
Wave velocities with the gunpowder blasts ranged from 379.2 to 465.4 meters per second, and from 351.5 to 412.4 meters per second with the firecracker explosions.
Duma and colleagues concluded that blast pressures and waves were not responsible for eye injuries caused by fireworks.
"This study provides information about injury mechanisms of fireworks that could aid in public policy decisions regarding fireworks laws and in the design of protective equipment," the researchers wrote.
The study also validates the previously developed calculation models for eye injury, they noted.
Limitations of this work included the use of cadaver eyes, with a resulting lack of data on how intracranial pressures could affect intraocular pressures, and the researchers' inability to directly measure the effects of injury in living tissue.
Last Updated: 7/3/2012