What is the mechanism of action of alpha-adrenergic agonists in lowering intraocular pressure?

• A. Increases aqueous humor production.
• B. Decreases outflow through scleral channels.
• C. Inhibits aqueous humor production and increases outflow.
• D. Blocks pupil dilation.

Answer: (C)

Alpha-adrenergic agonists lower intraocular pressure by both reducing the production of aqueous humor and increasing its drainage. They act on alpha-2 receptors in the ciliary body; activating these receptors suppresses aqueous production by lowering cAMP levels, which decreases secretion. At the same time, these agents can enhance outflow, particularly via the uveoscleral pathway, contributing to the overall IOP reduction. This dual action—inhibiting production and increasing outflow—fits best with the described mechanism. The other ideas don’t match how these drugs work: increasing production would raise IOP, reducing outflow would worsen it, and pupil dilation is not the mechanism by which these agents lower IOP.