A type of retina cell plays a more critical role in vision than previously known, a team led by Johns Hopkins University researchers has discovered.
Working with mice, the scientists found that the ipRGCs an atypical type of photoreceptor in the retina help detect contrast between light and dark, a crucial element in the formation of visual images. The key to the discovery is the fact that the cells express melanopsin, a type of photopigment that undergoes a chemical change when it absorbs light.
"We are quite excited that melanopsin signaling contributes to vision even in the presence of functional rods and cones," postdoctoral fellow Tiffany M. Schmidt said. Schmidt is lead author of a recently published study in the journal Neuron. The senior author is Samer Hattar, associate professor of biology in the university's Krieger School of Arts and Sciences. Their findings have implications for future studies of blindness or impaired vision.
Rods and cones are the most well-known photoreceptors in the retina, activating in different light environments. Rods, of which there are about 120 million in the human eye, are highly sensitive to light and turn on in dim or low-light environments. Meanwhile the 6 million to 7 million cones in the eye are less sensitive to light; they drive vision in brighter light conditions and are essential for color detection.
Rods and cones were thought to be the only light-sensing photoreceptors in the retina until about a decade ago when scientists discovered a third type of retinal photoreceptor the ipRGC, or intrinsically photosensitive retinal ganglion cell that contains melanopsin. Those cells were thought to be needed exclusively for detecting light for non-image-dependent functions, for example, to control synchronization of our internal biological clocks to daytime and the constriction of our pupils in response to light.
"Rods and cones were thought to mediate v
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Johns Hopkins University