What is the primary mechanism by which topical beta-blockers lower intraocular pressure?

• A. They increase uveoscleral outflow
• B. They decrease aqueous humor production by stimulating alpha receptors
• C. They decrease aqueous humor production by blocking beta-adrenergic receptors in the ciliary body
• D. They increase production of aqueous humor

Answer: (C)

Topical beta-blockers lower intraocular pressure mainly by reducing aqueous humor production from the ciliary body. They block beta-adrenergic receptors in the ciliary epithelium, which decreases cyclic AMP and suppresses the secretion of aqueous humor. With less fluid being formed, the pressure inside the eye drops.

This is different from drugs that increase outflow (such as prostaglandin analogs, which widen the uveoscleral pathway) or from mechanisms that rely on stimulating alpha receptors or increasing aqueous humor production. The key idea is production from the ciliary processes is diminished by beta-blockade.