THE INFLUENCE OF INTRAOCULAR PRESSURE ON THE TRANSSCLERAL DIFFUSION OF FITC–DEXTRAN 150

Abstract

Abstract: : Purpose: To evaluate the effects of intraocular pressure on the permeability of human sclera to FITC–Dextran 150, a compound with a molecular weight of 150 kD. Methods:The scleral permeability to FITC–Dextran (FD–150) was determined at transscleral pressures from 0 to 60 mm Hg. For each pressure 6 experiments were performed. Scleral sections excised from moist–chamber stored human globes were mounted in a two–compartment perfusion chamber. A small depot of drug (500 µl of 10^–4 M in BSS) was added to the episcleral surface. BSS was perfused to the choroidal side for up to 24 hours. Experiments were performed at transscleral pressures of 0, 15, 30, 60 mm Hg. Temperature was maintained at 37°C. Fractions of choroidal perfusate were collected and fluorescence was measured with a spectrofluorometer. From this data, scleral permeability K_trans (cm/sec) was calculated. Results:Human scleral permeability to FD–150 was significantly lower at 15 mm Hg compared to 0 mm Hg (P<0.05). No significant differences were observed between 15 and 60 mm Hg (P>0.05). Conclusions:Human sclera is permeable to compounds with a molecular weight of up to 150 kD. Permeability to FITC–Dextran was significantly decreased elevating pressure from 0 to 15 mm Hg, while no additional decrease was observed raising pressure from 15 to 60 mm Hg. These experiments suggest that transscleral delivery of high molecular weight compounds to the intraocular tissues is relatively unaffected by the pressure gradient provided by physiological intraocular pressures.

Keywords: sclera • intraocular pressure • retina