October 23, 2011 (Orlando, Florida) — Specular microscopy is a useful screening test for detecting occult ocular injury in veterans exposed to combat blast, and might prove useful as a baseline screening test before the deployment of military personnel, according to research presented here at the American Academy of Ophthalmology 2011 Annual Meeting.
"Many combat veterans with blast exposure have returned to civilian life without an eye examination, and may have occult closed-globe injuries," lead author Glenn Cockerham, MD, from the Veteran's Administration Health Care System and Stanford University, Palo Alto, California, told Medscape Medical News. "Cell density below 2000 cells/mm2, as measured by specular microscopy, should alert clinicians to the possibility of such injuries in these veterans and prompt a thorough ocular examination."
More than 200,000 American veterans are known to have been exposed in Iraq and Afghanistan to combat blasts powerful enough to cause traumatic brain injury, Dr. Cockerham said during a poster presentation. He and his group previously reported on the incidence of closed-globe injury in returning veterans (N Engl J Med. 2011;364:2172-2173).
"Ocular and adnexal tissues are exposed to powerful concussive accelerative and decelerative forces during blast exposure, as well as fragmentation from the bomb casing and other metal components. Since 2005, personnel engaged in combat have been required to wear protective polycarbonate eyewear to guard against fragmentation injuries," he said.
Corneal endothelial cells maintain corneal clarity and dehydration through active mechanisms, and are not felt to replicate in adult life. Noncontact specular microscopy is a safe and noninvasive way to visualize the corneal endothelium to evaluate endothelial cell density and morphology, he explained.
"Significant changes in these measures may be predictors of blast-induced ocular damage," he said.
In their study, Dr. Cockerham and his team performed specular microscopy on 61 subjects (58 men and 3 women) with blast-induced traumatic brain injury to evaluate the link between endothelial cell density and closed-globe intraocular injury. The median age of the subjects was 27 years (range, 18 to 42 years), and the median time since injury was 3 months (range, 2 weeks to 3 years). Twenty-six age and sex-matched noninjured subjects comprised the control group.
They found that 44% of the injured subjects had closed-globe ocular injury in at least 1 zone. Endothelial cell density below 2000 cells/mm2 was present in 40% of injured subjects. In comparison, none of the noninjured control group had endothelial cell density below that level (P < .001).
A cell density below 2000 cells/mm2 was a marker for closed-globe injury in all cases (P = .3). "This indicates that specular microscopy may be helpful in identifying veterans at high risk for intraocular injury. These patients should undergo a thorough eye evaluation, including gonioscopy and retinal examination with scleral depression," he said.
The researchers also found that endothelial cell-density values were significantly lower in blast subjects who reported wearing protective eyewear during the blast than in those who did not (P =.5).
"Our interpretation is that polycarbonate spectacles are protective against fragmentation and low-velocity projectiles, but not against blast waves," Dr. Cockerham said. "This may be because some of the acoustic frequencies are not affected by polycarbonate and penetrate into the eye, causing disruption of tissue interfaces, or because the semiflexible spectacle frames impact the cornea during a blast event. We have even found permanent facial scarring from polycarbonate spectacle frames in some of our subjects."
The researchers also found that endothelial cell density remained stable between the initial and 1-year follow-up visits. "This suggests that blast exposure may not lead to continuing decline in cell density, as is reported after surgical trauma," Dr. Cockerham said.
However, he added, "annual decline in normal endothelium is less than 1%, and our small sample size and follow-up of 1 year are not sufficient to detect small changes. Longer follow-up is required."
Because all subjects with cell density below 2000 cells/mm2 had intraocular injuries, using current specular microscopes in blast survivors might be useful as a screening test for such injuries, Dr. Cockerham concluded.
Dr. Cockerham has disclosed no relevant financial relationships..
American Academy of Ophthalmology (AAO) 2011 Annual Meeting: Abstract 088. Presented October 23, 2011.
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