Eyeworld

EW NEWS & OPINION 24 May 2017 Research highlight by Liz Hillman EyeWorld Staff Writer From here, Dr. Schwartz and his colleagues started making hypoth- eses, drawing upon related pub- lished research. Previous studies, Dr. Schwartz said, have established that overall spatial contrast and overall degree of focus in a visual scene controls eye growth. "That happens even when the optic nerve is cut, so it's not a signal from the brain; it's a signal in the eye that controls growth based on focus," Dr. Schwartz said. Other studies have established a correlation between time spent in indoors (indoor lighting) and myopia in children. And even more research has shown red/green con- trast, more common in indoor light situations, can lead to myopia in animal models as well. 2 "What my lab is trying to do here is put a 'how' in all of this. All of these have been brilliant ideas but all correlational. We know that some focus signal in the retina controls eye growth, we know that light has something to do with eye growth, but none of these studies could pinpoint a cell at all. [OND RGC] is potentially the missing link that gives us a cell that gives us the potential target down the line," Dr. Schwartz said. to make us think about whether it encodes a global feature of a scene rather than a local feature." Experimentally the researchers have identified 43 RGC types, be- lieving there are about 50 RGC types in the mouse retina, by presenting various spatial-temporal patterns of light ex vivo onto a projector on the retina and recording how each cell responds individually. Differentiat- ing these cells can be a challenge: some distinctions are obvious while others are more subtle, Dr. Schwartz said. "This one wasn't subtle at all," he added of OND RGC. "It has a delayed response by a lot." "One of our simplest stimuli to type cells is you flash a light from darkness on them," he continued. "Most cells in our conditions have a latency in their spiking from the onset of the light of about 100 milli- seconds; this one is about 500. It's a half a second, which is a long time. That and the lack of center surround antagonism, led us to think maybe this is not a cell that participates in active, conscious vision. When every other cell has already fired 400 mil- liseconds ago, why would you have one that waits so long?" fore. We just landed on this one that had this very strange and delayed response." Described in the Current Biolo- gy-published study as ON delayed (OND) retinal ganglion cell (RGC), this cell deviates from typical cen- ter-surround organization as seen in most RGCs and has an "unusually long latency to light stimulation," Dr. Schwartz and lead author of the study Adam Mani, postdoctoral fellow, Northwestern University Feinberg School of Medicine, wrote. 1 "Center-surround antagonism or lateral inhibition—there are multiple terms for it—it basical- ly means the ability to see spatial contrast.…They localize things in space, and one of the very interest- ing things about the cell we found is that it doesn't do that. Most cells, almost every retinal ganglion cell does that, and this one doesn't," Dr. Schwartz said, adding that intrinsi- cally photosensitive RGCs also don't exhibit center surround antagonism. "Center surround antagonism helps retinal ganglion cells encode infor- mation about a small area of space. They look at some small part of the world and that's how you have high resolution in your world, so the fact that this cell didn't have it, started Cell could be possible target for medical therapy, especially for genetic conditions A newly discovered retinal ganglion cell has been described as possibly involved in driving myo- pia, potentially linked to the amount of time a child spends indoors. The discovery could be the target of new therapies especially for genetic forms of myopia. Researchers at Northwestern University, Chicago, have been trying to "reverse engineer the ret- ina," as Greg Schwartz, PhD, lead investigator of the latest study and assistant professor of ophthalmolo- gy, Northwestern University Fein- berg School of Medicine, put it. "We're trying to understand the functions of…all the retinal gan- glion cells and their connectivity to be able to build a diagram of the retina so that in the future people can make more advanced artificial retinal prostheses," he explained. "We're studying all sorts of differ- ent retinal ganglion cells that do all sorts of different things that haven't been reported in the literature be- Researchers discover retinal cell they think could be related to myopia

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