To the Editor.
—I found the article by Kondo and Araie1 regarding fluorouracil concentrations after subconjuctival injection of interest, but I believe that their experimental design poses some problems with extrapolation of the results to the clinical situation.In their model, the drug was injected in a superotemporal location, permitting gravity to assist in the movement of both the subconjunctival and tear-borne fluorouracil inferiorly. Clinically, however, the filter site is most often located superiorly and the injection site inferiorly; thus, the drug must diffuse against the combined forces of gravity and aqueous outflow through the fistula. Even if there is no subconjunctival scarring, the injected drug is unlikely to diffuse and "rapidly reach the conjunctiva and sclera on the side 180° away from the injection site" in the clinical situation at the rate demonstrated in the Kondo and Araie's model.The reported even distribution (1.6 to 2.4 μg/g) of
Ball SF. Concentration Change and Activity of Fluorouracil in the External Segment of the Eye After Subconjunctival Injection. Arch Ophthalmol. 1989;107(9):1276-1277. doi:10.1001/archopht.1989.01070020346003