When used in combination with prostaglandin analogs (PGAs), carbonic anhydrase inhibitors provide an additional decrease in intraocular pressure (IOP) of how many mmHg?

• A. 4-5
• B. 2-3
• C. 3-4
• D. 5-6

Answer: (C)

Using a carbonic anhydrase inhibitor alongside a prostaglandin analog adds a modest extra drop in intraocular pressure, typically about 3–4 mmHg. This happens because they work through different mechanisms: prostaglandin analogs mainly increase outflow through the uveoscleral pathway, while carbonic anhydrase inhibitors reduce aqueous humor production by inhibiting the enzyme in the ciliary body. Since the effects target separate parts of the IOP regulation system, they sum together rather than interfere, giving that additive reduction. The exact amount can vary with baseline IOP and individual response, but 3–4 mmHg is the commonly observed add-on effect.