Which nerves control pupil size?

Which nerves control pupil size?

• A. Oculomotor
• B. Optic
• C. Facial
• D. Trigeminal

Answer: (A)

Pupil size is controlled by autonomic nerves that regulate the iris muscles. The constriction of the pupil is produced by the parasympathetic fibers that travel with the oculomotor nerve. These fibers originate in the Edinger–Westphal nucleus, synapse in the ciliary ganglion, and then reach the sphincter pupillae through the short ciliary nerves to narrow the pupil in bright light or when focusing on near objects. The dilation of the pupil, while not driven by this same nerve, involves the sympathetic pathway from the brainstem to the dilator pupillae. The optic nerve is the sensory pathway for vision and participates in the pupillary light reflex by conveying light information to the brain, but it does not directly control pupil size. The facial and trigeminal nerves do not innervate the iris muscles involved in constriction or dilation.

Pupil size is controlled by autonomic nerves that regulate the iris muscles. The constriction of the pupil is produced by the parasympathetic fibers that travel with the oculomotor nerve. These fibers originate in the Edinger–Westphal nucleus, synapse in the ciliary ganglion, and then reach the sphincter pupillae through the short ciliary nerves to narrow the pupil in bright light or when focusing on near objects. The dilation of the pupil, while not driven by this same nerve, involves the sympathetic pathway from the brainstem to the dilator pupillae.

The optic nerve is the sensory pathway for vision and participates in the pupillary light reflex by conveying light information to the brain, but it does not directly control pupil size. The facial and trigeminal nerves do not innervate the iris muscles involved in constriction or dilation.