Which pupil change is associated with sympathetic activation?

• A. Pupil dilation
• B. Pupil constriction
• C. No change
• D. Blepharospasm

Answer: (A)

Pupil dilation is the change you see when the sympathetic system is active. The eye has two iris muscles: the dilator pupillae (radial) and the sphincter pupillae (circular). When the sympathetic nerves fire, norepinephrine targets the dilator pupillae, causing it to contract and the pupil to enlarge (mydriasis). This helps you take in more light and improves vision during arousal or in darker settings. Pupil constriction, by contrast, comes from the parasympathetic system acting on the sphincter pupillae. Blepharospasm is an eyelid spasm and doesn’t change pupil size, and no change isn’t consistent with the autonomic control of the iris.