Diphenhydramine as a topical ocular anesthetic.

OBJECTIVE

To determine whether 5% diphenhydramine solution has an anesthetic effect when administered topically to rabbit corneas.

DESIGN

Experimental study.

PARTICIPANTS

Twenty white New Zealand rabbits.

METHODS

Twenty rabbits at the University of Arkansas for Medical Sciences received 1 drop of 5% diphenhydramine solution in the left eye and 1 drop of balanced salt solution in the right eye. Corneal sensation was then measured with a Cochet-Bonnet esthesiometer at 30-, 60-, and 90-minute intervals. Rabbits were observed for conjunctival reaction. Follow-up fluorescein and Rose Bengal slit-lamp examinations were then performed to assess toxicity.

RESULTS

Diphenhydramine solution at a 5% concentration demonstrated a significant anesthetic effect 30, 60, and 90 minutes after instillation (p < 0.0001, p = 0.0001, p = 0.0164, respectively). Mild conjunctival injection occurred in all diphenhydramine-treated eyes. No toxic effects on the corneal epithelium were observed.

CONCLUSIONS

When applied topically to rabbit corneas, 5% diphenhydramine solution has a significant anesthetizing effect compared with salt solution (control eyes). Topical diphenhydramine may be a safe alternative in patients requiring topical anesthesia who have multiple allergies to topical anesthetics. Additional studies are needed to determine a dose-response curve and to further evaluate corneal toxicity prior to use in humans.