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Tuesday / June 18.
HomeminewsRare Cell in Retina May Indicate Glaucoma

Rare Cell in Retina May Indicate Glaucoma

Researchers are developing a new test that would catch glaucoma earlier and more accurately than current tests which rely on human input.

Scientists hypothesise that a recently discovered, rare cell in the retina, 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 United States Glaucoma Research Foundation, it’s estimated that only half of those with glaucoma, know it.

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…

“By the time someone has detectable symptoms of glaucoma, irreversible damage has likely already occurred,” said Prof. Hartwick. “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 Prof. Hartwick and other researchers has shown that the ipRCGs’ response time is very slow, indicating 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 Professor Hartwick.

“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.”

Professor 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 per cent 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 Professor Zadnik.

Professor Hartwick’s next steps are to continue refining the measurement technology and then to start testing it in patients with glaucoma.