Permeability of human cornea and sclera to sulfonamide carbonic anhydrase inhibitors

Corneal penetration of sulfonamide carbonic anhydrase inhibitors for topical treatment of glaucoma has been tested in human eye bank and rabbit tissue. Paired corneas, with the epithelia intact or removed, and excised sclera were perfused in vitro. Corneal permeability (Kp) to methazolamide and ethoxzolamide was similar in both species, but for benzolamide and bromacetazolamide the Kp was greater in humans. Human corneas without epithelium had Kp the same as scleral Kp. Topical methazolamide (6 mmol/L) was studied in vivo in rabbits and in ten humans before cataract surgery. The mean (+/- SE) concentration in the rabbit aqueous was 3.2 +/- 1.4 mumol/L at eight minutes and 1.2 +/- 0.16 mumol/L at one hour. In humans, less than 0.2 mumol/L was detected at eight minutes; at one hour none was detected in three cases, and 0.4 +/- 0.08 mumol/L was detected in four cases. Lower permeability in humans than rabbits may result from a fourfold greater blinking rate, a twofold greater tear turnover, and a twofold lower corneal/conjunctival area.