Which medication is a beta blocker that decreases aqueous humor production?

• A. Timolol 0.5%
• B. Brimonidine 0.1%
• C. Dorzolamide
• D. Latanoprost

Answer: (A)

Beta blockers lower intraocular pressure mainly by reducing aqueous humor production from the ciliary processes. They block beta-adrenergic receptors there, lowering cellular cAMP and the active secretion of aqueous humor. Timolol 0.5% is a nonselective topical beta-adrenergic blocker that achieves this production decrease, making it the classic choice for lowering aqueous formation.

The other drugs use different mechanisms. Brimonidine is an alpha-2 agonist that both reduces production and can increase outflow; dorzolamide is a carbonic anhydrase inhibitor that decreases aqueous formation by inhibiting bicarbonate production; latanoprost is a prostaglandin analog that mainly increases outflow, with only a modest effect on production.