Effects of changing the direction of gravity on sector pupil dilations

To study anterior segment aqueous humor kinetics by using sector pupil dilations with different directions of gravity to change the direction of convectional flow in the anterior chamber.

Sector pupil dilations were elicited using focal applications of phenylephrine at the limbus. To vary the direction of gravity (and hence the direction of convectional flow) relative to the eye, subjects' heads were tilted left side down or right side down with gaze horizontal. Pupil elongation and pupil center displacement were measured as functions of time.

Early stages of pupil dilation were dominated by pupil elongation toward the site of drug application. Amplitude of elongation was about the same for all the application points, but center displacement depended on the application point. Later stages of pupil dilation showed an interaction between the site of drug application and the direction of gravity.

The results are interpreted in terms of anterior chamber convectional flow and its interaction with transpupillary aqueous flow and diffusion. Early distribution in the anterior segment of a substance applied to the limbus appears to be determined primarily by local diffusion, whereas later distribution is affected by movement of the drug in convectional and transpupillary flow.