The effect of acetazolamide on the retinal circulation.

The effect of the carbonic anhydrase inhibitor, acetazolamide, on the retinal circulation was studied in 10 healthy volunteers. Acetazolamide was administered intravenously at a dose of 500 mg. Retinal blood flow was determined from red cell velocity using laser Doppler velocimetry and vessel diameter measurement using computerised digital image analysis of monochromatic fundus photographs. There was a significant increase in retinal blood flow at 30 minutes and 60 minutes after acetazolamide injection (p = 0.002). Retinal vessels showed vasodilatation reaching significant levels 60 minutes after the injection (p < 0.03). An increase in red cell velocity was observed at 30 and 60 minutes (p < 0.002). A significant reduction in intraocular pressure occurred at 30 and 60 minutes after the injection (p < 0.001). The mechanisms responsible for the increase in retinal blood flow acted via significant increases in perfusion pressure (p < 0.05), red cell velocity (p < 0.002) and retinal vessel dilatation (p < 0.03). An increase in tissue PCO2 and a reduction in pH are thought to be responsible for the vascular dilatation. The increase in retinal blood flow with acetazolamide may serve to limit optic disc and retinal ischaemia in acute glaucoma and central retinal artery occlusion respectively.