pupillary light reflex
Quick Summary
The pupillary light reflex is the involuntary constriction of the pupil in response to bright light. This reflex helps regulate the amount of light entering the eye, protecting the retina from damage and improving visual clarity.12
When light shines on one eye, both pupils constrict. This bilateral response occurs because nerve fibers from the optic nerve partially cross over in the brain, allowing signals from one eye to affect both sides. The constriction is controlled by the iris muscles, which are innervated by the parasympathetic nervous system. Conversely, pupils dilate in dim light to allow more light to enter.132
The pupillary light reflex is a crucial part of neurological and eye examinations, as abnormalities can indicate underlying issues within the visual system.2
Ask Britannica AI about this topic
Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.
