Melanopsin

Melanopsin is an Opsin with a Peak Wavelength of 480nm. Unlike Photopsins (Cones) and Rhodopsins (Rods), Melanopsins are not part of any “image-forming” visual system. They are located inside special Retinal Ganglion Cells (nerve cells) in the retina and their primary functions are believed to be regulating the sleep-wake cycle (Circadian rhythm) through release of Melatonin, and regulating the size of the pupil.

Melanopsin was only discovered only in 1999, when mice engineered without Cone and Rod cells – and therefore blind – were still able to maintain their Circadian Rhythm.