Which drug is a direct muscarinic agonist used to lower intraocular pressure in glaucoma?

• A. Epinephrine
• B. Pilocarpine
• C. Aminopentamide
• D. Fentanyl

Answer: (B)

Direct muscarinic agonists lower intraocular pressure by activating muscarinic receptors in the eye to increase aqueous humor outflow. Pilocarpine does exactly this: it stimulates M receptors on the sphincter pupillae and ciliary muscle, causing pupil constriction (miosis) and contraction of the ciliary muscle. The muscle changes open the drainage angle and enhance outflow through the trabecular meshwork, reducing resistance and lowering intraocular pressure. Other listed drugs don’t act as direct muscarinic agonists in the eye—epinephrine works mainly through adrenergic receptors, whereas aminopentamide is an anticholinergic and fentanyl is an opioid—so they don’t produce the same direct muscarinic effects needed to reduce intraocular pressure.