Acetazolamide has been shown experimentally to facilitate the transport of water across the retinal pigment epithelium (RPE) from the subretinal space to the choroid.1 Cox et al2 found that carbonic anhydrase inhibitors were effective in promoting the absorption of intraretinal fluid in some cases of cystoid macular edema (CME), and they proposed that these drugs would be most effective in disorders in which the leakage came from the RPE rather than from the retinal vasculature. However, Fishman et al3 found them to be most effective against parafoveal retinal vascular edema in retinitis pigmentosa.
There may be a simple explanation for these differing observations. Water is transported across the RPE in conjunction with a net movement of ions (particularly sodium chloride and bicarbonate), and the mammalian RPE membrane contains several active and facilitated transport systems that regulate traffic of those ions.4 These drugs are presumed to work
Marmor MF. Hypothesis Concerning Carbonic Anhydrase Treatment of Cystoid Macular Edema: Example With Epiretinal Membrane. Arch Ophthalmol. 1990;108(11):1524-1525. doi:10.1001/archopht.1990.01070130026013