Measurement of aqueous humor flow by fluorophotometry in the presence of a dilated pupil.

PURPOSE To determine by means of fluorophotometry whether pharmacologic dilation of the pupil can interfere with the measurement of aqueous flow. METHODS Ten normal human volunteers underwent dilation with tropicamide, phenylephrine, and a combination of the two drugs. Before and after dilation, the rate of aqueous flow was measured by the rate of disappearance of fluorescein from the cornea and the anterior chamber. RESULTS Dilation of the pupil with tropicamide alone had no effect on the rate of clearance of fluorescein. Dilation with phenylephrine increased the rate of clearance of fluorescein by 40% and caused a small increase in the variability among subjects. Dilation with a combination of tropicamide and phenylephrine caused clearance of fluorescein at more than double the normal rate and a marked increase in variability among subjects. CONCLUSIONS When the pupil is dilated sufficiently to permit mixing of aqueous humor in the posterior and anterior chambers, fluorescein can leave the system by a posterior route, and its rate of clearance may not be an accurate measure of the net rate of aqueous humor flow through the anterior chamber.