What is the mechanism of action of carbonic anhydrase inhibitors in glaucoma therapy?

• A. Inhibits aqueous humor production.
• B. Increases aqueous humor outflow.
• C. Blocks beta receptors.
• D. Alters osmotic gradient.

Answer: (A)

Carbonic anhydrase inhibitors reduce intraocular pressure by dampening the production of aqueous humor. They block carbonic anhydrase in the ciliary body, which normally converts CO2 and water into bicarbonate and protons. Bicarbonate is transported into the fluid that becomes aqueous humor, driving fluid secretion. When this enzyme is inhibited, bicarbonate formation drops, the active transport of ions and water into the anterior chamber decreases, and less aqueous humor is produced. The net effect is lower intraocular pressure. These agents (topical dorzolamide, brinzolamide; systemic acetazolamide) mainly reduce production rather than increase outflow, and they can have systemic or local side effects.