A comparative study of the efficacy and tolerability of topical corneal anaesthetics

Abstract

There are several topical anaesthetics available to the optometrist as a preservative-free unit dose formulation. There is little comparative data as to the efficacy and tolerability of these drugs. The aim of this study was to compare the depth and duration of corneal anaesthesia following instillation of one drop of 0.4% benoxinate, 0.5% amethocaine and 0.5% proxymetacaine. The tolerability of each anaesthetic was assessed using a linear 10-point arbitrary comfort scale. Fourteen male subjects participated in the study (mean age 26.6 + 5.0 years). Corneal sensitivity was measured using a slit-lamp mounted Cochet-Bonnet aesthesiometer prior to installation, and at 1, 3, 5, 10, 15, 20, and 30 min after, and continued if necessary until corneal sensitivity had returned to pre-instillation levels. For each anaesthetic complete anaesthesia occurred within 1 min of instillation and a return to baseline sensitivity levels occurred by 30 min. No significant difference in anaesthesia was found between drugs at each time point. In contrast tolerability profiles indicated that proxymetacaine was significantly better tolerated than either amethocaine (P < 0.01) or benoxinate (P < 0.001). This together with an excellent safety record makes proxymetacaine an ideal choice for optometric procedures requiring short-acting corneal anaesthesia.