Newswise — COLUMBUS, Ohio – By exploiting a recently discovered cell in the retina, researchers are developing a new glaucoma test that would catch the blindness-causing disease earlier and more accurately than current tests that rely on human input. Scientists hypothesize that this rare cell, which reacts very slowly to changes in light, may help clinicians more accurately identify which patients are candidates for early interventions that can help slow the disease’s progression.
“Tests for glaucoma, particularly those that rely on quick exposure to bright light and subjective human observation or feedback, may actually be missing the early signs of glaucoma,” said Andrew Hartwick, OD, PhD, assistant professor at the College of Optometry at The Ohio State University who is leading the research to find a more sensitive screening tool.
Glaucoma, the second leading cause of blindness in the world, disrupts the flow of communication between the eye and the brain when pressure from extra fluid in the eye slowly destroys the optic nerve and retinal ganglion cells (RGCs). These cells line the inner-most layer of the retina and serve to transmit information about light and images to the brain. The loss of ganglion cells is so gradual that according to the Glaucoma Research Foundation, it’s estimated that of the 2.2 million Americans who have glaucoma, only about half know it.
“By the time someone has detectable symptoms of glaucoma, irreversible damage has likely already occurred,” noted Hartwick, who is also an assistant professor of neuroscience at Ohio State's College of Medicine. “We know there’s probably a lot happening on a microscopic level in the early stages of the disease that we just can’t detect yet.”
A rare group of retinal ganglion cells, called intrinsically photoreceptive RGCs (ipRCGs), were only discovered during the last decade. IpRCGs represent less than one percent of ganglion cells in the retina but play a critical role in communicating the presence of light to the brain in ways that affect the sleep cycle and pupil size.
Previous research conducted by Hartwick and other researchers have shown that the ipRCGs’ response time is very slow, indicating that these cells are unable to distinguish between flickering and continuous light. Two common glaucoma tests used by doctors are the automated visual field test that determines a patient’s ability to see flashes of light or the “swinging flashlight” test to observe how quickly the pupil reacts to light; however, these tests won’t pick up any deficits in the slower-reacting ipRCGs.
“The primary problem with the visual field test is that it relies on people to accurately report what they are seeing, and that doesn’t always happen. Secondarily, the test uses flashes of light that stimulate other cells in the retina but doesn’t tap into the slow ipRCGs, where you might be able to sensitively detect a change in response because there are so few of them,” said Hartwick.
Realizing that he might be able to leverage the ipRCGs’ sluggish properties to develop a new glaucoma test, Hartwick applied for and won KL2 funding from the Ohio State’s federally-funded Center for Clinical and Translational Science (CCTS) to test his hypothesis and to create an objective pupil test that could measure ipRCG function.
“We’ve shown that we can isolate the ipRCG response from other photoreceptors in healthy patients and that we can quantify those responses objectively with technology that’s already used in many optometrists’ and ophthalmologists’ offices,” said Hartwick, who recently shared some of his early findings at the American Academy of Optometry annual meeting.
Through the CCTS funding, Hartwick’s research is also being mentored by Karla Zadnik, OD PhD, the Glenn A. Fry Professor in Optometry and Physiological Optics and Associate Dean at Ohio State’s College of Optometry. Zadnik noted that she’s hopeful the research could lead to a clinical test that is used in conjunction with the tonometry test, another common in-office test that measures the pressure of the fluid inside the eye.
“Tonometry is an excellent tool, but when you consider that only ten percent of people who have high eye pressure actually go on to get glaucoma, a considerable number of people might have to take unnecessary medications to prevent something they ultimately won’t get. It would be great to have additional information to help identify the highest risk patients,” said Zadnik.
Hartwick’s next steps are to continue refining the measurement technology and then to start testing it in patients with glaucoma.
According to the Glaucoma Research Foundation, it is estimated that there may be more than 60 million cases of glaucoma worldwide. Risk factors include being over the age of 60, a family history of glaucoma, diabetes, and severe nearsightedness. African Americans are 15 times more likely to be visually impaired from glaucoma than Caucasians, and glaucoma accounts for nineteen percent of all blindness among African Americans.
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About The Ohio State University Center for Clinical and Translational ScienceDedicated to turning the scientific discoveries of today into the life-changing health innovations of tomorrow, The Ohio State University Center for Clinical and Translational Science (CCTS) is a collaboration of experts including scientists and clinicians from six Ohio State Health Science Colleges, Ohio State’s Wexner Medical Center and College of Medicine, and Nationwide Children’s Hospital. Funded by a multi-year Clinical and Translational Science Award (CTSA) from the National Institutes of Health, OSU CCTS provides financial, organizational and educational support to biomedical researchers as well as opportunities for community members to participate in credible and valuable research. The CCTS is led by Rebecca Jackson, M.D., Director of the CCTS and associate dean of research at Ohio State. For more information, visit http://ccts.osu.edu.
About the Clinical and Translational Science Awards Launched in 2006 by the NIH, and currently residing in the National Center for the Advancement of Translational Sciences (NCATS), the Clinical and Translational Science Awards (CTSA) program created academic homes for clinical and translational science at research institutions across the country. The CTSA’s primary goal is to accelerate discoveries towards better human health by speeding up the time it takes for basic science to turn into useable therapeutics and to train the next generation of clinicians and translational researchers.
The Ohio State University Center for Clinical and Translational Science (CCTS) is funded by the National Institutes of Health (NIH) Clinical and Translational Science Award (CTSA) program (grants 8UL1TR000090-05, 8KL2TR000112-05, and 8TL1TR000091-05) The CTSA program is led by the NIH’s National Center for Advancing Translational Sciences (NCATS). The content of this release is solely the responsibility of the CCTS and does not necessarily represent the official views of the NIH.
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