Mydriatic effects using low concentrations of phenylephrine hydrochloride.

The dose response relationship of different concentrations of phenylephrine with and without prior application of topical anesthetic was measured to determine the minimum concentration which produced maximum mydriasis. As little as 0.125% phenylephrine caused mydriasis in some subjects and maximum mydriasis was achieved with 2%. Concentrations greater than 2% produced very little additional mydriasis. A therapeutically effective dose could be as low as 1% with prior installation of a topical anesthetic.