Part 4/12:
The human eye houses specialized photoreceptors called intrinsically photosensitive retinal ganglion cells (ipRGCs). Unlike rods and cones, which are responsible for visual perception, ipRGCs are sensitive to blue light and relay information directly to brain regions that control internal clocks and mood regulation.
Interestingly, some of these cells continue to function even in individuals who are blind but retain eye health, allowing them to subconsciously synchronize their internal rhythms to the light-dark cycle. Disruption of this pathway—whether through eye damage or environmental factors—can lead to sleep disturbances and mood disorders, highlighting the vital link between light perception and mental health.