Pivenfrine is a sympathomimetic agent. Pivenfrine is an analog of phenylephrine hydrochloride (PE) ten times more potent as a mydriatic. It is a product of the esterification of a molecule of pivalic acid (PA) to the p-hydroxyl group of PE. It is, therefore, more lipophilic than PE is, and penetrates the cornea more readily. Pivenfrine is called a prodrug of PE because it is enzymatically hydrolyzed to the active, parent compound (PE), and to PA, before reaching its desired active site in the eye. The pivenfrine-treated corneas without epithelium significantly increased in thickness, whereas no change in thickness was observed in corneas with epithelium intact.