Rhodopsin vision in the dark. Several closely related opsins differ only in a few amino acids and in the wavelengths of light that they absorb most strongly. Humans have eight other opsins besides rhodopsin, as well as cryptochrome (light-sensitive, but not an opsin). The photopsins are found in the cone cells of the retina and are the basis of color vision. They have absorption maxima for yellowish-green (photopsin I), green (photopsin II), and bluish-violet (photopsin III) light. The remaining opsin, melanopsin, is found in photosensitive ganglion cells and absorbs blue light most strongly. In rhodopsin, the aldehyde group of retinal is
Intrinsically photosensitive retinal ganglion cells Intrinsically photosensitive retinal ganglion cells Intrinsically photosensitive retinal ganglion cells (ipRGCs), also called photosensitive retinal ganglion cells (pRGC), or melanopsin-containing retinal ganglion cells (mRGCs), are a type of neuron in the retina of the mammalian eye. The presence of ipRGCs were first noted in 1923 when rodless, coneless mice still responded to a light stimulus through pupil constriction, suggesting that rods and cones are not the only light sensitive neurons in the retina. It wasn't until the 1980s that advancements in research on these cells began. Recent research has shown that these retinal ganglion cells, unlike other retinal ganglion cells,