Effect of proparacaine on tropicamide-induced mydriasis

The use of a topical anesthetic before the instillation of a mydriatic is recommended in order to enhance both the rate and magnitude of pupillary dilation. However, there is a paucity of data supporting the prior use of topical anesthetics with tropicamide, the most commonly used mydriatic agent in optometric practice. Therefore, we conducted a study to determine the clinical effect of proparacaine on tropicamide-induced pupillary dilation.

We investigated the effects of prior instillation of 0.5% proparacaine (Ophthetic) on pupillary dilation with 0.5% tropicamide (Mydriacyl) using a double-blind, placebo-controlled protocol on two groups of young adult subjects. Thirty subjects, aged between 18 and 30 years, were divided into 2 groups of 15, based on whether they had light- or dark-colored irides. The pupils of both eyes of each subject were dilated with tropicamide, but only one eye, chosen at random, received proparacaine (experimental condition), whereas the other was administered a saline placebo (control condition). Pupil diameter was measured using a ruler and magnifying loupe.

Subjects with light-colored irides had a greater average pupil dilation than subjects with dark-colored irides. There was a small, statistically significant difference in pupil diameter between the control and experimental conditions, but only for subjects with light-colored irides. The rate of pupillary dilation to peak pupil diameter and the rate of decrease in pupil diameter after peak pupil diameter was reached did not differ between experimental conditions or subject groups.

Although prior instillation of topical proparacaine produced a statistically significant difference in pupil diameter for subjects with light-colored irides, the result was not clinically significant. Therefore, we do not recommend the use of a topical anesthetic before tropicamide-induced mydriasis for young adult patients.