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
Giant retinal ganglion cells an S-Off, (L + M)-On opponency. Their spatial modulation transfer function is low-pass, with an upper limit of about 0.6 cycles per degree. Dacey "et al". propose that the giants subserve the subconscious, 'non-image-forming' functions of circadian photoentrainment and pupillary diameter, and via the rod and cone inputs, may help mediate conscious perception of irradiance. Giant retinal ganglion cells Giant retinal ganglion cells are photosensitive ganglion cells with large dendritic trees discovered in the human and macaque retina by Dacey "et al". (2005). Giant retinal ganglion cells contain a photo-pigment, melanopsin, allowing them to respond directly to light. They also