True or False: All drug classes have additive IOP lowering effect to each other.

• A. True
• B. False
• C. Not sure
• D. Sometimes

Answer: (A)

The main idea is that combining drugs from different classes often yields an additive decrease in intraocular pressure because they work through distinct mechanisms in the eye. One class typically reduces the production of aqueous humor, while another class increases its outflow, so the total effect is greater than using a single agent. This is why multi-drug regimens that pair different mechanisms are common in glaucoma care: you can achieve more IOP lowering by engaging multiple pathways. Of course, when two drugs share the same mechanism, the additional benefit may be smaller due to a ceiling effect, but overall, selecting agents from different classes tends to produce additive (and sometimes synergistic) reductions in IOP.