Limbal microvasculature of the rat eye

To define the microvascular anatomy of anterior segment blood supply and aqueous drainage in the rat eye.

External limbal blood vessels were studied by direct inspection of normal, living rat eyes and eyes injected intracamerally with fluorescein dye. Intraocular connections of these vessels were then documented with scanning electron microscopy of methylmethacrylate microvascular luminal castings.

The rat limbus possesses a circumferential vascular ring consisting of a single artery and a venous plexus. The limbal artery communicates with radial anterior ciliary arteries and with perforating arterioles arising from the long posterior ciliary arteries. The venous plexus is connected to a circumferential Schlemm's canal by numerous transcleral, aqueous-containing collector channels and drains into multiple radial veins located within the episclera.

These findings illustrate anatomic similarities between rats and primates, both in anterior segment blood supply and aqueous humor drainage. The rat limbal artery provides collateral perfusion of the anterior segment from anterior and long posterior ciliary systems. The direct communications between identifiable external aqueous-containing veins, a circumferential episcleral venous plexus, and an internal Schlemm's canal provides the anatomic basis for producing chronically elevated intraocular pressure in rats using retrograde injection of mild sclerosing agents into the aqueous humor outflow pathways, and for administering drugs and other agents to the entire trabecular meshwork and Schlemm's canal.