Drugs causing mydriasis are best described as which class?

• A. Anti-ACH drugs (anticholinergic)
• B. Diazepam
• C. Dopamine agonists
• D. Beta blockers

Answer: (A)

Mydriasis from drugs occurs when parasympathetic control of the pupil is blocked. The iris constrictor muscle (sphincter) is activated by muscarinic acetylcholine receptors; when an anticholinergic drug blocks these receptors, constriction is inhibited and the dilator muscle, driven by sympathetic input, predominates, causing dilation. That makes anticholinergic medications the classic class associated with mydriasis. Diazepam is a benzodiazepine acting on GABA-A receptors and is not a typical cause of dilation. Dopamine agonists affect dopaminergic pathways and aren’t known for a mydriatic effect as a class. Beta blockers don’t produce dilation; they mainly serve to reduce aqueous production with little impact on pupil size.