Probing anterior segment kinetics with focally applied mydriatics

The purpose of this study was to examine the effects of convectional flow and anterior segment configuration on drug kinetics. Mydriatics were applied focally at the limbus in order to produce sector dilation of the pupil. Subjects were tested with either tropicamide or phenylephrine, applied at the superior, temporal, inferior, or nasal limbus (or as a conventional drop). Changes in pupil form were analyzed by means of photography, digitization, and circular Fourier series representation. Both tropicamide and phenylephrine were found to produce sector dilation; however, phenylephrine was approximately twice as effective. Applications at the superior limbus were significantly less effective than applications at the inferior limbus. The results are interpreted in terms of anterior segment convectional flow, which is believed to play a substantial role in pharmacokinetics of the anterior segment.