USE OF FLUOROMETRY IN ASSESSING THE EFFICACY OF A CATION-SENSITIVE GEL AS AN OPHTHALMIC VEHICLE - COMPARISON WITH SCINTIGRAPHY

Gelrite, a heteropolysaccharide that forms a gel in the presence of cations, was tested in humans for its efficacy as an ophthalmic vehicle by a noninvasive fluorometric technique. Fluorescein was used as the tracer, and its concentration in the anterior chamber was used as the principal measure of bioavailability. The gel afforded a twofold increase in penetration of fluorescein compared with an isotonic buffer solution; this increase is slightly more than can be obtained with simple viscous vehicles. The increase in penetration caused by Gelrite was confirmed by measurements of the contact time of fluorescein in the tear film with the cornea. Earlier experiments with scintigraphy suggested a considerably greater contact time of fluorescein with the cornea when Gelrite was used. However, this increased contact time may be because the technique also measures radioactive tracer that had dried out on the lid margins. Accordingly, significant quantities of fluorescein could be eluted from the lids after the penetration experiments were completed.