DOD-Funded Researcher Studies TBI-Related Photophobia

Featured speaker Andrew Hartwick, O.D., Ph.D. (Ohio State University College of Optometry)

On March 18, AEVR hosted a deployment-related vision trauma research Congressional Briefing entitled Understanding Light Sensitivity in Patients with Traumatic Brain Injury (TBI) featuring clinician-scientist Andrew Hartwick, O.D., Ph.D. (Ohio State University College of Optometry). Funded through a Hypothesis Development Award (see box below) from the Department of Defense’s (DOD) Peer Reviewed Vision Research Program (VRP), his research addresses a major DOD-identified gap: the lack of understanding of the physiological causes of photophobia, or light sensitivity. Photophobia is a symptom frequently reported by troops who have suffered a TBI resulting from exposure to the blast from an Improvised Explosive Device (IED). Other visual symptoms of TBI include loss of focus, oculomotor deficits, and visual field deficits. TBI is the most prevalent warfighter injury, with 300,000 soldiers experiencing it between years 2000-2014. It is also a common cause of injury in the civilian population, resulting from falls, automobile accidents, and sports-related injuries.

Dr. Hartwick’s research focuses on intrinsically photosensitive retinal ganglion cells, or ipRGCs, which are cells in the eye that are particularly sensitive to blue light. They express the photo-pigment melanopsin and play a key role in a number of non-visual functions, including the regulation of the body’s circadian rhythms. He theorized that exposure to a TBI caused these cells to “overreact” to light, thereby signaling to the brain that ambient light levels are brighter than they actually are. In a previous, done in collaboration with Satchin Panda, Ph.D. (Salk Institute) and other researchers, evidence from experiments on young mouse pups supported a role for ipRGCs in photophobia. The young mice “froze” and stopped moving when exposed to light but, after being injected with a compound that inhibits melanopsin function, this light aversion behavior was no longer present.

Dr. Hartwick’s current DOD-funded research focuses on individuals who have been diagnosed with “mild” TBI, meaning that they were not in a coma after the injury, and who had also experienced chronic photophobia for a minimum of 6 months. A central problem for clinicians is lack of an objective tool to measure the extent of photophobia that patients experience; they are simply asked if exposure to light causes them any discomfort. With his team, Dr. Hartwick initiated the Head Injury-associated Photosensitivity and Pupillary function (HIPP) study to evaluate whether exposure to a TBI caused an alteration in the ipRGC contribution to light-evoked pupil constriction. A total of 40 subjects were enrolled in the study, including 28 TBI patients with photophobia and 12 control subjects. The researchers exposed subjects to alternating flashes of blue and red light and measured the change in pupil size during the light pulses and the rate at which the pupil re-dilated during the intervening dark periods. As ipRGCs continue to respond for many seconds after light offset, this latter measurement provided an objective measurement of the signal relayed by these cells to the brain center responsible for regulating the pupillary light reflex.

The data suggest that ipRGCs were not hypersensitive to bright light in the subjects with TBI-associated photophobia, as originally theorized, but there was evidence for a change in the ability of ipRGCs to adapt to repeated light exposure in these subjects. These results support the premise that ipRGC function can be altered after TBI, and this dysfunction can be detected using a short pupil test that is adaptable for clinical use. With a better understanding of the physiological processes in the eye that are causing the photophobia, the next step is the development of a therapeutic intervention that could “re-set” the ipRGCs to return to a normal response to light. In particular, many of the subjects experienced some level of relief from their photophobia through the use of relatively inexpensive orange-tinted glasses. Future research will further investigate whether this benefit is specific to certain tints, and examine the effect of long-term wear of these glasses on ipRGC function.

The Briefing was co-sponsored by Research to Prevent Blindness (RPB), Blinded Veterans Association (BVA), and the Association for Research in Vision and Ophthalmology (ARVO).

Congressman Gene Green (D-TX), co-chair of the Congressional Vision Caucus, gave an introduction to the briefing. He serves on the House Energy and Commerce Committee.	Dr. Hartwick with Glenn Minney, Blinded Veterans Association’s Legislative Director, who lost his vision due to exposure to an IED while serving in Iraq
Dr. Hartwick with Alicia Kerry Mica from the American Optometric Association

Under the auspices of NAEVR, Dr. Hartwick also made Ohio delegation office visits:

Dr. Hartwick with John Crown from the office of Senator Sherrod Brown (D-OH), who serves on the Senate Veterans Affairs Committee. Mr. Crown, who served two tours of duty in Iraq, related how his superior officers emphasized the importance of troops wearing their protective eye gear when heading onto patrol. Senator Brown’s office has requested FY2016 VRP funding at $15 million, per NAEVR’s request.

Dr. Hartwick with Tyler Brace from the office of Senator Rob Portman (R-OH)