The effect of intraocular pressure on human and rabbit scleral permeability.

PURPOSE The purpose of this study was to evaluate the effects of intraocular pressure on the permeability of human and rabbit sclera to water, dexamethasone, 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 microl) was added to the episcleral surface while perfusing an irrigating solution slowly across the choroidal side. The perfusate was collected and scleral permeability calculated. Experiments were performed at 0, 15, 30, and 60 mm Hg for each compound in human and rabbit tissue. RESULTS Analysis of variance showed a significant effect of intraocular pressure on both human and rabbit scleral permeability. Human scleral permeability was decreased by as much as a factor of two for water (P = 0.0004), dexamethasone (P<0.0001), and carboxyfluorescein (P = 0.0064) at elevated intraocular pressures. Rabbit scleral permeability was similarly affected by 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 from 15 to 60 mm Hg can decrease scleral permeability to small molecules by one half when compared with the sclera with no pressure applied.