The effects of carbonic anhydrase inhibitors on aqueous humor chemistry and dynamics

The effects of topical application of the carbonic anhydrase inhibitor trifluormethazolamide (TFM) on intraocular pressure (IOP), ascorbate and CO2 concentrations in aqueous humor, and aqueous humor flow were studied in rabbits. These effects were compared with those produced by systemic treatment with methazolamide. The decrease in IOP observed after TFM was accompanied by changes in the composition of the aqueous humor. Posterior aqueous ascorbate concentration showed a marked increase (up to 1.7-fold), whereas the anterior aqueous ascorbate did not change significantly. Similar changes were found in rabbits after systemic treatment with methazolamide. A small but statistically significant decrease in the CO2 content of both posterior and anterior aqueous was observed after topical TFM application. Methazolamide yielded a more profound lowering in the CO2 content of the aqueous humor, a reflection of the significant decrease in plasma CO2 content. For topical TFM or systemic methazolamide doses yielding complete inhibition of carbonic anhydrase in the eye, a 55-59% reduction of aqueous flow was calculated from the ascorbate data using the Kinsey and Palm equation. However, a 31-42% reduction in aqueous flow was obtained from the same data using an equation based only on posterior chamber data. The reasons for using only posterior aqueous ascorbate data for calculating the changes in aqueous humor flow are discussed.