Which nerves are involved in the pupillary light reflex?

The pupillary light reflex is a physiological response that involves two primary cranial nerves to regulate the amount of light entering the eye.12

• Afferent Pathway: The sensory input is carried by the optic nerve (CN II). Light detected by the retina is transmitted through the optic nerve to the midbrain, specifically the pretectal nucleus.123
• Efferent Pathway: The motor response is mediated by the oculomotor nerve (CN III). Parasympathetic fibers originating in the Edinger-Westphal nucleus travel via the oculomotor nerve to the ciliary ganglion, ultimately stimulating the sphincter muscle of the iris to constrict the pupil.1

Because the pretectal nuclei project to the Edinger-Westphal nuclei on both sides of the brain, the reflex is bilateral; illuminating one eye causes both pupils to constrict.12