What is the primary role of intrinsically photosensitive retinal ganglion cells (ipRGCs)?

• A. Color vision
• B. Visual acuity
• C. Circadian rhythm entrainment
• D. Depth perception

Answer: (C)

The main function of intrinsically photosensitive retinal ganglion cells is to regulate the body’s internal clock by signaling ambient light to the brain’s circadian center, the suprachiasmatic nucleus. Their melanopsin-driven signals help entrain sleep-wake cycles and melatonin production in response to day-night light changes, linking lighting conditions to circadian timing. This is distinct from color vision, visual acuity, or depth perception, which rely on the image-forming pathway through rods and cones and the visual cortex. ipRGCs also contribute to pupil reflex, but their primary relevance in everyday design is supporting circadian entrainment through appropriate light exposure.