Identification of the mouse uveoscleral outflow pathway using fluorescent dextran.

PURPOSE: This study was undertaken to assess directly whether there is uveoscleral outflow in the mouse eye by monitoring the movement of intracamerally injected fluorescent dextran. METHODS: After anesthesia, NIH Swiss mice received intracameral injection of 1.5 microL of 0.2 pg/microL 70-kDa dextran conjugated to tetramethyl-rhodamine and to lysine. After survival times of 10, 20, 60, and 120 minutes, the experiments were terminated by transcardial perfusion with 2% paraformaldehyde. The eyes were enucleated and embedded in paraffin, and sections were prepared. These sections were then analyzed by fluorescence microscopy. RESULTS: Fluorescent tracer in the eyes of animals that survived for 10 minutes was prominent in the iris root and ciliary processes and was of moderate intensity in the adjacent sclera. Moderate intensity fluorescence also was observed in the trabecular meshwork and adjacent cornea. At 20 minutes, intense fluorescence was observed in the ciliary processes and the ciliary muscle. This fluorescence in the ciliary muscle extended from the posterior edge of the ciliary muscle's tail into the anterior choroid. At 60 minutes, the fluorescence in the choroid extended to the equator and adjacent sclera. The intensity of the fluorescence within the ciliary processes of these eyes was substantially reduced when compared with the 20-minute-survival eyes. At 120 minutes, label was observed only within trabecular meshwork and Schlemm's canal. CONCLUSIONS: These results indicate that at least a portion of aqueous outflow in the mouse eye is through the uveoscleral outflow pathway.