Anesthetic effects from low concentrations of proparacaine and benoxinate.

Using double masking procedures, the response to McKay-Marg and Goldmann tonometry of 361 randomly selected patients was determined following the installation of a single dose of either 0.125, 0.25 or 0.5% proparacaine or 0.1, 0.2 or 0.4% benoxinate. Examiners graded the adequacy, patient tolerance and conjunctival hyperemia induced by the drop, while the subjects reported on the sting of the drop, awareness of the tonometer and discomfort after the procedure. The results indicate that 0.25% proparacaine is an effective anesthetic dose on all patients and that 0.2% benoxinate and 0.125% proparacaine would be effective on patients over age 40. The implication of these results is that significantly lower doses of anesthetic can be used which will result in less stinging, reduced hyperemia and shorter duration of action.