Ocular pharmacokinetics and convectional flow: evidence from spatio-temporal analysis of mydriasis.

Pupil shape and placement were studied during pharmacologic dilation, using a photographic technique. Dilation onset was highly asymmetric; typically, the inferior or inferior-nasal side of the pupil moved maximally, while the opposite side barely moved. Pupil shape tended to elongate at a large angle to the direction of maximum shift. Late in dilation, pupils returned to more circular shape and pupil centers returned to near their original position. Results when a subject's head was inverted during and immediately after drug administration were essentially unchanged. However, results when a subject's head was rolled on one side (and kept there) after administration were markedly different; the dilation pattern shifted roughly in accord with head tilt. It is proposed that anterior chamber convectional flow is responsible for the asymmetry. Supportive evidence was obtained from experiments in which cooled or heated gel-packs were applied to the lids. Analysis indicates that convectional flow makes a very substantial contribution to anterior segment pharmacokinetics and is also likely to be of general importance in anterior segment transport.