A 62-year-old man with primary open-angle glaucoma is started on oral acetazolamide, and his intraocular pressure falls. The drug lowers pressure by:

• A Increasing outflow through the trabecular meshwork
• B Osmotically drawing water out of the vitreous humour
• C Increasing uveoscleral outflow directly
• D Inhibiting carbonic anhydrase in the ciliary processes and reducing aqueous humour formation ✓

Explanation

Aqueous humour is actively secreted by the non-pigmented epithelium of the ciliary processes, a process dependent on carbonic anhydrase for bicarbonate transport. Acetazolamide blocks this enzyme, reducing secretion rate and hence intraocular pressure. It does not act on trabecular or uveoscleral outflow pathways; those are targets of prostaglandin analogues and miotics. Osmotic agents such as mannitol, not acetazolamide, dehydrate the vitreous.

Reference: Katzung Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.