In this basic science presentation, Dr. Do discusses the key role of intrinsically photosensitive retinal ganglion cells (ipRGCs) in processing light signals and explains the tri-stable states of the melanopsin pigment, which are essential for circadian clock function and nonimage vision. Image vision enables object recognition, while nonimage vision senses overall light intensity to regulate circadian rhythms, sleep, pupil response, and hormonal activity. Rods and cones express visual pigments that trigger downstream signaling in response to light, producing an electrical signal that is transmitted to retinal ganglion cells through the optic nerve.

ipRGCs process light signals either through rods and cones or independently of them, transmitting signals that influence pupil dilation, circadian rhythm, melatonin production, photophobia, and pain responses. Ablation of ipRGCs removes most light-responsive functions. Humans and primates have the highest visual acuity and contrast resolution due to the fovea, which is unique to these species. Located in the center of the macula, the fovea has a high density of cones that degenerate in age-related macular degeneration (AMD). This degeneration suggests that replacing foveal cones could be a potential approach for cell therapies targeting AMD.