A drug that causes pupillary dilation belongs to which category?

• A. Anticholinergics
• B. Opioids
• C. Parasympathomimetics
• D. Beta-adrenergic Blockers

Answer: (A)

Pupillary dilation happens when the parasympathetic control that normally constricts the pupil is blocked. Anticholinergic drugs block muscarinic receptors, so the parasympathetic signal to the sphincter pupillae is diminished and the pupil relaxes toward the dilated state driven by the sympathetic muscles. That’s why this category best explains dilation.

Opioids, in contrast, commonly cause miosis (pupil constriction) due to increased parasympathetic activity. Parasympathomimetics stimulate the same muscarinic receptors that cause constriction, leading to smaller pupils. Beta-adrenergic blockers don’t primarily produce dilation; they don’t actively drive the sympathetic dilation of the pupil.