Which statement best describes the mechanism of action of cholinergic agonists in glaucoma treatment?

• A. Increases aqueous humor production.
• B. Decreases outflow through the sclera.
• C. Increases trabecular outflow (however not really used for chronic therapy).
• D. Inhibits ciliary muscle contraction.

Answer: (C)

Cholinergic agonists lower intraocular pressure by increasing trabecular outflow through contraction of the ciliary muscle. When these drugs stimulate muscarinic receptors in the ciliary muscle, the muscle contracts, pulling on the trabecular meshwork and opening the channels in Schlemm’s canal. This reduces resistance to aqueous humor drainage along the conventional outflow pathway, lowering IOP. They do not raise aqueous production, nor do they act by reducing scleral (uveoscleral) outflow, and they produce contraction rather than inhibit it. Because of side effects like pupil constriction, blurry vision, and tolerance with long-term use, these agents are less favored for chronic therapy and are more often used in acute settings or specific short-term indications.