Penetration of hydrogen peroxide from contact lenses or tear-side solutions into the aqueous humor

Contact lenses were soaked in hydrogen peroxide (H2O2) solutions of 1 to 20 mM (34 to 680 ppm) and placed on isolated rabbit corneas to determine whether H2O2 could penetrate across the tissue into the artificial aqueous humor used to perfuse the endothelial surface. Corneas with intact epithelium allowed no H2O2 to cross into the perfusing fluid even with the lenses containing the highest (20 mM) concentration of peroxide. If the epithelium was removed a transient pulse of H2O2 appeared in the perfusing fluid only from lenses with 10 or 20 mM H2O2. The cornea metabolized H2O2 rapidly (the rate varying with the concentration) and thus the small quantities of H2O2 in the contact lenses (less than 400 nmol at 20 mM) are destroyed before diffusing across the entire thickness of the cornea. When the contact lens was replaced by a 0.8 ml saline containing H2O2, and renewed every 15 min, H2O2 crossed the intact cornea to the perfusing fluid when its concentration at the epithelium was between 3 and 4 mM. Should such larger quantities be presented to the epithelium (for example, in eye drops) the concentration, volume, and duration of exposure will determine whether H2O2 enters the anterior chamber. It is concluded that in the clinical situation of typical contact lens use in an eye with intact epithelium neither the corneal endothelium nor other intraocular tissues will be damaged by residual concentrations of H2O2 up to 680 ppm, whether in single or daily events.