Question

A girl has her eyes shut and is standing inside a brightly lit room. What happens
to her pupils when she opens her eyes? Why?

Answer 1

Her pupils will constrict (get smaller) — the pupillary light reflex. When she opens her eyes more light hits the retina, retinal ganglion cells send signals via the optic nerve to the pretectal area and bilaterally to the Edinger–Westphal nuclei. Parasympathetic fibers in the oculomotor nerve travel to the ciliary ganglion and then to the sphincter pupillae muscle, causing rapid miosis (direct and consensual constriction). This limits retinal illumination and improves image quality; the opposite (dilation) is produced by the sympathetic system.