Acetazolamide effect on the inward permeability of the blood-retinal barrier to carboxyfluorescein.

The inward permeability of the blood-retinal barrier to carboxyfluorescein was determined in 12 cynomolgus monkeys. Probenecid (175 mg/kg), an inhibitor of active outward transport of carboxyfluorescein, did not affect the inward permeability, indicating that the inward permeability is independent of the active outward transport system. However, acetazolamide (20 mg/kg), which causes increased outward fluid movement across the retinal pigment epithelium (RPE), significantly reduced the inward permeability. Thus, inward diffusion of carboxyfluorescein interacts with outward fluid flow across the RPE. Since carboxyfluorescein has low lipid solubility and remains extracellular, it is concluded that the pathway of fluid movement and carboxyfluorescein diffusion across the RPE is paracellular.