DOES TOPICAL HYDROGEN-PEROXIDE PENETRATE THE CORNEA

Purpose. To determine under what conditions hydrogen peroxide (H2O2) c an penetrate the cornea and cause increased concentrations of H2O2 in the aqueous humor. Methods. Rabbit corneas were exposed in vitro and i n vivo to H2O2 concentrations up to 60 mmol/l either in a 600 mul volu me or as consecutive drops. H2O2 was measured over time either in the endothelial superfusate or in tapped samples of aqueous humor, and in the fluid applied to the ocular surface. The stability of exogenous H2 O2 added directly to aqueous humor was also determined. Results. Exoge nous H2O2 in aqueous humor decays with a half-life of 20 minutes, chie fly as a result of catalase activity. When applied to the entire ocula r surface, 600 mul of 60 mmol/l H2O2 caused no change in the concentra tion in aqueous humor, but when applied to the corneal surface alone, penetration occurred at 18 mmol/l and above. When applied as eight 40- mul drops to the ocular surface the threshold for H2O2 penetration was above 36 mmol/l. Conclusions. H2O2 is rapidly eliminated on the ocula r surface, chiefly by enzyme activity of the conjunctiva and cornea. T hreshold for penetration of H2O2 into the aqueous humor depends on vol ume, concentration, duration, and ocular surface exposed. In a healthy eye, exogenously derived H2O2 is eliminated by enzyme activity of the aqueous humor and tissues surrounding the anterior chamber.