Melanopsin Looks on the Bright Side of Life
Better known as the light sensor that sets the body's biological clock, melanopsin also plays an important role in vision: Via its messengers—so-called melanopsin-expressing retinal ganglion cells, or mRGCs—it forwards information about the brightness of incoming light directly to conventional visual centers in the brain, Satchin Panda and his collaborators reported in PLoS Biology.
"Millions of people worldwide suffer varying degrees of blindness because of rod and cone degeneration or dysfunction, but many of them can still perceive differences in brightness," says Panda, an assistant professor in the Regulatory Biology Laboratory. "Melanopsin-expressing RGCs typically survive even complete rod and cone loss and could explain the light responses under these conditions," he adds.
Melanopsin, a photopigment that measures the intensity of incoming light, is fundamentally different from the classical rod and cone opsins, which help us see. For one, it is much less sensitive to light and has far less spatial resolution— characteristics that fit perfectly with this light sensor's primary function of signaling changes in ambient light levels to the brain throughout the day.
"The density of mRGCs in the retina is too low for any meaningful resolution but if we could express melanopsin in a greater number of cells, we might be able to increase resolution to a point that allows blind people to safely navigate their environment," he says.