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

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

Answer: (A)

Direct stimulation of muscarinic receptors in the eye can lower intraocular pressure by increasing drainage of the aqueous humor. Pilocarpine is a direct muscarinic agonist; when applied as eye drops, it activates M3 receptors on the ciliary muscle, causing contraction that opens the trabecular meshwork and enhances aqueous outflow. This mechanism directly reduces the pressure inside the eye, making pilocarpine the classic agent described as a direct agonist for glaucoma management.

Epinephrine is a direct adrenergic agonist, and while it can influence IOP through different pathways, it does not act on ocular muscarinic receptors and is not the typical direct cholinergic agent used for this purpose. Aminopentamide is a muscarinic antagonist, which would inhibit cholinergic effects rather than promote them. Oxymorphone is an opioid analgesic with no role in lowering IOP.