A team of researchers at Northwestern University has discovered a type of retinal ganglion cell that may cause myopia when it dysfunctions. The study is published in the journal Current Biology.
This image shows an ON Delayed retinal ganglion cell. Image credit: Adam Mani & Gregory W. Schwartz, Northwestern University.
This study is part of the team’s larger body of research to reverse engineer the retina by identifying new retinal cell types in mice.
It was authored by Gregory Schwartz, assistant professor of ophthalmology at Northwestern University Feinberg School of Medicine, and Adam Mani, a postdoctoral fellow in ophthalmology at Feinberg.
“The retina has about 50 types of retinal ganglion cells, which together convey all the information we use to perceive the visual world,” the authors explained.
“Each of these cells provides different visual information — such as color or motion — about any point in space.”
The newly-identified retinal cell, dubbed ON Delayed, is highly sensitive to light. It controls how the eye grows and develops.
“More than a billion people in the world have myopia, whose incidence is rising and is linked to how much time people spend indoors as children,” Dr. Schwartz said.
“This discovery could lead to a new therapeutic target to control myopia.”
If the ON Delayed cell instructs the eye to grow too long, images fail to be focused on the retina, causing nearsighted vision and a lifetime of corrective glasses or contact lenses.
“The eye needs to stop growing at precisely the right time during childhood,” Dr. Schwartz said.
“It has long been long known the retina contains a signal to focus the image in the eye, and this signal is important for properly regulating eye growth during childhood.”
“But for years no one knew what cell carried the signal. We potentially found the key missing link, which is the cell that actually does that task and the neural circuit that enables this important visual function,” he said.
To conduct the study, the researchers used microscopic glass electrodes to record electrical signals from cells in a mouse retina while presenting patterns of light on a digital projector.
The ON Delayed cell was unique among many other cell types tested in its exquisite sensitivity to whether an image was in focus.
Dr. Schwartz described the neural circuit as the diagram that reveals how this cell is wired to other cells in the retina to acquire this unique sensitivity.
“The indoor light spectrum has high red/green contrast, which activates these clusters of photoreceptors in the human eye, creating the equivalent of an artificial contrast image on the retina,” he said.
“It’s likely the human version of the ON Delayed retinal ganglion cell would be overstimulated by such patterns, causing aberrant over-growth of the eye, leading to myopia.”
The researchers now plan to find a gene specific to the ON Delayed retinal ganglion cell. Then they can turn its activity up or down in a genetic mouse model to try to induce or cure myopia.
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Adam Mani & Gregory W. Schwartz. Circuit Mechanisms of a Retinal Ganglion Cell with Stimulus-Dependent Response Latency and Activation Beyond Its Dendrites. Current Biology, published online January 26, 2017; doi: 10.1016/j.cub.2016.12.033
This article is based on a press-release from Northwestern University.
