April 2019

NEWS

Blast-induced ocular trauma
Damage sometimes takes weeks to present


by Liz Hillman EyeWorld Senior Staff Writer

A pig eye, its sclera blue from dye, sits in a 3D-printed model eye socket. This configuration is placed into a “blast tube” ready to get hit with a “pure blast”—no fragments, no heat, just a shock wave of pressure.
Taken from the tube after the blast, Tonia Rex, PhD, examines the eye. On the surface, everything looks fine; all of its structures are intact. Nothing seems to be out of place, at least at first glance. And that’s exactly the point Dr. Rex wants to make.
Residents and other attendees of the 33rd Triservice Ocular Trauma Workshop could see how an eye exposed to the blast might look fine. But Dr. Rex’s research has found that while an eye exposed to a blast may look normal immediately afterward, vision loss can occur in the weeks after the incident.
“If the eye looks grossly fine, and the anterior chamber looks fine, it’s not thought about,” she said. “That’s the problem because a blast wave does not have to cause damage—and typically does not to the anterior structures. Yet you can have vision loss from damage to visual pathways from the back, the optic nerve, the retina, and also from visual pathways in the brain.”
Dr. Rex has been researching blast-induced ocular injury since 2010 through grants from the U.S. Department of Defense Vision Research Program. Her initial goal was to create a model of blast-induced ocular injury to understand what happens to the eye and its structures in a blast to develop appropriate therapies. She and her team have discovered that different injury characteristic results are based on the blast’s energy. If there is a blunt force component, for example, retinal detachments are more common. However, if even a lower pressure blast is repeated, such as in large IEDs due to reverberations of blast waves and impact from physical objects, a different type of damage can occur.
“We’re not getting retinal detachments, but instead the amount of damage to the optic nerve goes up dramatically. There is something about the physics of that mechanical injury that the optic nerve is particularly susceptible to, so we’re getting a lot of axon degeneration in the optic nerve,” Dr. Rex said, adding that axon degeneration can happen weeks after the initial event.1
“We completed a time course that suggests secondary degeneration doesn’t even get going until almost 2 weeks out,” she said.
This delay could allow time for vision-saving treatments to be initiated, but physicians must realize that even if the eye looks healthy, damage could present weeks later.
“These individuals will look fine initially. Later they develop the pathology that can be seen by a clinician. For example, with this indirect, traumatic optic neuropathy, oftentimes the optic disc looks fine on presentation. The pallor that’s indicative of optic nerve degeneration won’t develop until weeks later,” Dr. Rex said.
She recommends that if someone has been exposed to a blast, had a traumatic brain injury, or been in potential trauma environments and are reporting problems with their vision that they be referred to an ophthalmologist for follow-up.
In terms of treatment for the cell death that can occur as a result of blast exposure, Dr. Rex’s research has shown a link between oxidative stress and neuroinflammatory pathways. In a series of experiments published in Cell Death & Disease, she and coinvestigators treated mice with high levels of antioxidants, then exposed them to injury, looking for indicators of oxidative stress, markers of neuroinflammation, and secondary degeneration.2 They found that by reducing oxidative stress with antioxidant pretreatments, neuro-oxidative pathways were blocked, preserving axons and visual function.
Preliminary research suggests taking antioxidants even after exposure may be effective in at least blunting the effects, Dr. Rex said. She doesn’t see any harm in recommending antioxidants to patients exposed to a blast.
“Vitamin C is great because you can’t take too much. It’s water soluble so if you have too much in your system, it will leave your system. Reasonable levels of vitamin E should be safe, too.”
In terms of anterior damage that isn’t immediately apparent if there is not fragment or heat damage to the cornea, Dr. Rex said they have observed disruption to the tear film, which is usually temporary and recovers with drop use.

About the doctor
Tonia Rex, PhD
Associate professor
Associate director for research
Vanderbilt Eye Institute
Vanderbilt University Medical Center
Nashville, Tennessee

References

1. Vest V, et al. Rapid repeat exposure to subthreshold trauma causes synergistic axonal damage and functional deficits in the visual pathway in a mouse model. J Neurotrauma. 2019. Epub ahead of print.
2. Bernardo-Colon A, et al. Antioxidants prevent inflammation and preserve the optic projection and visual function in experimental neurotrauma. Cell Death Dis. 2018;9:1097.

Financial interests
Rex
: None

Contact information
Rex
: tonia.rex@Vanderbilt.Edu

Blast-induced ocular trauma Damage sometimes takes weeks to present Blast-induced ocular trauma Damage sometimes takes weeks to present
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