Mydriasis with different preparations of topically administered lidocaine hydrochloride

To quantify the mydriatic effect and side effects of topical lidocaine hydrochloride with different pH values and concentrations in healthy volunteers.

Umeå University Hospital Eye Clinic, Umeå, Sweden.

In this intraindividual comparison double-masked randomized study, healthy volunteers were given topical lidocaine 8%, lidocaine 8% pH 6.0, or a placebo 3 times at 90-second intervals. Thereafter, a drop of tropicamide 0.5% or placebo was given (tropicamide setting). Another group of healthy volunteers was given topical lidocaine 4%, 8%, or 16% 3 or 6 times at 90-second intervals (dose-response setting). Before and 15, 30, 60, and 180 minutes after eyedrop instillation, the near point was determined and Scheimpflug photography was performed.

The tropicamide setting comprised 26 volunteers (mean age 23.5 years) and the dose-response setting, 10 volunteers (mean age 24.5 years). The direct mydriatic effect of lidocaine was larger at pH 6.0 (mean peak effect 0.61+/-0.06 [SEM] versus 0.42+/-0.04 mm) (P< .05), and the augmentation of tropicamide mydriasis was larger at pH 6.0. Lidocaine 8% had a better direct mydriatic effect than lidocaine 4% and lidocaine 16% (mean peak effect 0.60+/-0.09 mm versus 0.19+/-0.08 mm and 0.28+/-0.10 mm, respectively) (P< .01). Lidocaine 16% given 6 times caused corneal side effects.

Lidocaine 8% with pH 6.0 had a maximum direct mydriatic effect and gave maximum augmentation of tropicamide mydriasis without causing unwanted corneal side effects and thus should be preferable for topical anesthesia in cataract surgery.