The effect of intraocular pressure on human and rabbit scleral permeability

PURPOSE. The purpose of this study was to evaluate the effects of intraocul ar pressure on the permeability of human and rabbit sclera to water, dexame thasone, and carboxyfluorescein. METHODS. Scleral sections excised from moist-chamber-stored human globes or eyes obtained from euthanatized New Zealand White rabbits were mounted in a perfusion chamber that can create a transscleral pressure that simulates an intraocular pressure. A small depot of drug (100 mu l) was added to the episcleral surface while perfusing an irrigating solution slowly across the choroidal side. The perfusate was collected and scleral permeability calcu lated. Experiments were performed at 0, 15, 30, and 60 mm Hg for each compo und in human and rabbit tissue. RESULTS. Analysis of variance showed a significant effect of intraocular pr essure on both human and rabbit scleral permeability. Human scleral permeab ility was decreased by as much as a factor of two for water (P = 0.0004), d examethasone (P < 0.0001), and carboxyfluorescein (P = 0.0064) at elevated intraocular pressures. Rabbit scleral permeability was similarly affected b y elevated intraocular pressure for water (P = 0.0039), dexamethasone (P = 0.0001), and carboxyfluorescein (P = 0.0016). CONCLUSIONS. This study shows that simulated intraocular pressure ranging f rom 15 to 60 mm Hg can decrease scleral permeability to small molecules by one half when compared with the sclera with no pressure applied.