Abstract
Over the last 20 years, researchers have tried to understand the photoreceptor mechanisms which regulate the circadian system. The discovery of the novel photoreceptor, melanopsin-expressing retinal ganglion cells (mRGCs), aroused researchers' interest in the role of the eye in non-image-forming visual functions such as circadian rhythm regulation and pupillary light reflex. The mechanisms by which the mRGC regulates non-visual/visual functions in humans have not been established, but some researchers have reported that these cells differ from rods and cones in many respects. In the present report, I overview prior studies for the mRGC, and discuss the role of the mRGC which contributes to non-visual/visual pathways with aspects of morphology, neurophysiology and biology.
