This study identifies melanopsin as the visual pigment in retinal ganglion cells (RGCs) that project to the suprachiasmatic nucleus (SCN), the brain's primary circadian pacemaker. Melanopsin is found in a subset of RGCs and is responsible for intrinsic photosensitivity, enabling these cells to detect light and regulate circadian rhythms and non-image-forming visual functions such as the pupillary light reflex. Unlike rods and cones, which are not required for photoentrainment, melanopsin-positive RGCs directly respond to light and project to the SCN and other brain regions involved in circadian regulation and light reflexes. The study used molecular techniques to clone and characterize melanopsin, and immunohistochemistry to identify its distribution in RGCs. The results show that melanopsin is expressed in the cell bodies, dendrites, and proximal axons of RGCs, with a higher density in the superior and temporal quadrants of the retina. These RGCs project to the SCN and other brain regions, and their intrinsic photosensitivity is confirmed by their melanopsin expression. The findings suggest that melanopsin is the photopigment responsible for the light sensitivity of RGCs that regulate circadian rhythms and non-image-forming visual functions. The study also highlights the role of melanopsin-positive RGCs in various brain regions, including the intergeniculate leaflet (IGL), ventral lateral geniculate (VLG), and pretectum, which are involved in circadian photoentrainment and the pupillary light reflex. The results support the idea that melanopsin-containing RGCs are generally involved in non-image-forming visual functions.This study identifies melanopsin as the visual pigment in retinal ganglion cells (RGCs) that project to the suprachiasmatic nucleus (SCN), the brain's primary circadian pacemaker. Melanopsin is found in a subset of RGCs and is responsible for intrinsic photosensitivity, enabling these cells to detect light and regulate circadian rhythms and non-image-forming visual functions such as the pupillary light reflex. Unlike rods and cones, which are not required for photoentrainment, melanopsin-positive RGCs directly respond to light and project to the SCN and other brain regions involved in circadian regulation and light reflexes. The study used molecular techniques to clone and characterize melanopsin, and immunohistochemistry to identify its distribution in RGCs. The results show that melanopsin is expressed in the cell bodies, dendrites, and proximal axons of RGCs, with a higher density in the superior and temporal quadrants of the retina. These RGCs project to the SCN and other brain regions, and their intrinsic photosensitivity is confirmed by their melanopsin expression. The findings suggest that melanopsin is the photopigment responsible for the light sensitivity of RGCs that regulate circadian rhythms and non-image-forming visual functions. The study also highlights the role of melanopsin-positive RGCs in various brain regions, including the intergeniculate leaflet (IGL), ventral lateral geniculate (VLG), and pretectum, which are involved in circadian photoentrainment and the pupillary light reflex. The results support the idea that melanopsin-containing RGCs are generally involved in non-image-forming visual functions.