Concentration-dependent effects of lidocaine on corneal epithelial wound healing

Local anesthetic toxicity is a recognized clinical problem that has limited the use of topical corneal anesthetics for pain relief after corneal abrasion. Studies have shown clinically administered concentrations (0.5-2%) of local anesthetics impair corneal reepithelialization. Unfortunately, instillation of local anesthetic drops into an eye does not provide a measurable, steady-state concentration of drug. Thus, it has not been possible to evaluate whether there is an analgesic concentration of local anesthetic that does not impair corneal wound healing. Using the new in vitro rabbit cornea wound healing model, the effect of steady-state lidocaine concentrations on epithelial wound healing was examined. At lidocaine concentrations below 100 micrograms/ml, wound healing was not impaired. Higher concentrations (250-1000 micrograms/ml) resulted in dose-dependent impairment of epithelial wound healing. Combined with electrophysiologic evidence that corneal nerve injury discharge can be abolished by lidocaine concentrations less than 100 micrograms/ml, this research suggests that topical lidocaine in low concentration may be a safe topical corneal analgesic.