Which agent increases trabecular meshwork outflow?

• A. Brimonidine
• B. Dorzolamide
• C. Pilocarpine
• D. Timolol

Answer: (C)

Muscarinic stimulation of the ciliary muscle increases drainage through the conventional outflow pathway. Pilocarpine, a direct muscarinic agonist, causes ciliary muscle contraction. This pulls on the scleral spur and widens the spaces in the trabecular meshwork and Schlemm’s canal, reducing resistance and boosting outflow of aqueous humor, which lowers intraocular pressure.

Other agents mainly reduce production of aqueous humor or have only modest effects on outflow through the trabecular pathway, rather than directly opening the trabecular meshwork. Brimonidine lowers IOP largely by decreasing production and modestly increasing uveoscleral outflow; dorzolamide and timolol reduce production as well.