Non-Visual Photoreception

The light sensitive portion of the eye, the retina, signals the brain about the pattern, intensity, and wavelength of light striking the retina. However, this information is used for more than just seeing. A special class of retinal neurons called melanopsin retinal ganglion cells (mRGCs) mediate behaviors that depend on light, but not on vision. These behaviors include constriction of our pupils and photoentrainment, the synchronization of our brain’s internal clock (i.e. circadian pacemaker) with the external environment. Melanopsin, for which these cells are named, is a light sensing protein that makes mRGCs intrinsically photosensitive. In other words, mRGCs can respond to light without the help of the rod and cone photoreceptors responsible for vision. Given mRGCs’ ability to see without additional input from other retinal neurons, it is surprising that mRGCs are, in fact, extensively connected to the rest of the retina. They receive a constant barrage of information derived from rods and cones about the light striking the retina. The goals of my research include determining the role of these inputs role in computing light levels. Specifically, we measure the contribution of rod and cone derived input on the estimate of mean light levels (i.e. irradiance) in visual environments with differing degrees of contrast (i.e. variance around the mean light level).

(James Demas)