Comparison of the tolerability and efficacy of unit-dose, preservative-free topical ocular anaesthetics.

Several topical ocular local anaesthetics are available in preservative-free unit-dose applicators. There is little comparative data as to the efficacy and tolerability of these drugs. The purpose of this study was to compare the tolerability, and the depth and duration of corneal anaesthesia following instillation of one drop of 0.4% oxybuprocaine (benoxinate), 0.5% amethocaine, or 0.5% proxymetacaine. The tolerability of each anaesthetic was assessed using a linear ten point arbitrary comfort scale. A group of 14 healthy male subjects, with a wide variation in iris pigment levels, participated in the study (mean age 26.6 years, range 18-40 years). Corneal sensitivity was measured using a slit-lamp mounted Cochet-Bonnet aesthesiometer prior to instillation, and at 1, 2, 5, 10, 15, 20 and 30 min after instillation, 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 45 min. No significant difference in anaesthesia was found between the drugs at each time point. Tolerability profiles indicated that proxymetacaine was significantly better tolerated than either amethocaine (p < 0.01) or oxybuprocaine (benoxinate) (p < 0.001). There was considerable inter-subject variability in the duration of anaesthesia, and practitioners should be alert to this when allowing patients to leave the practice following the production of corneal anaesthesia. There seems little to choose clinically between the three active agents as regards clinical effectiveness. Proxymetacaine was significantly better tolerated than either amethocaine or oxybuprocaine.