USE OF FLUORESCEIN-LABELED DEXTRANS IN INVESTIGATION OF AQUEOUS-HUMOR OUTFLOW IN RABBIT

The anterior chamber of the rabbit eye was perfused with solutions containing fluorescein-labeled dextrans (FD) of various MW from 3000-150,000. Using an adapted Zeiss slit-lamp, specially modified for rapid sequence flash photography, the outflow channels for the aqueous humor in the limbal region were demonstrated in living, anesthetized animals. Semi-permanent preparations showing the postmortem distribution of FD in the tissues were made by fixation in a mixture of neutral formaldehyde and 70% ethanol. The fixed material was dehydrated in the normal way and either cleared in bulk in methyl salicylate or embedded in paraffin for sectioning. Cleared whole-mount preparations showed FD precipitated in the angular aqueous plexus and the efferent veins together with some perivascular distribution. Paraffin sections showed that FD had penetrated into the tissues of the iridocorneal angle and the suprachoroidal space. Further experiments were carried out using closed cycle perfusion of the anterior chamber with a mixture of FD (MW 3000, 40,000 or 150,000) and blue dextran (MW 2,000,000). Rate constants calculated for the loss of these substances from the anterior chamber showed that the rates for the FD were 20-25% greater than the rate for blue dextran. An appreciable fraction of aqueous humor in the rabbit eye may leave via a uveoscleral route.