Evidence of a New Uveolymphatic Outflow Pathway in Human and Sheep: Implications for Aqueous Humor Drainage and Glaucoma

Abstract

Purpose: : To determine whether a lymphatic circulation exists within the human and sheep ciliary body, and if present, its relationship to aqueous humor outflow.

Methods: : Twelve normal human eyes with no history of ocular disease, atherosclerosis or stroke were obtained from the Eye Bank of Canada. Human eye sections were triple-immunostained with D2-40(Signet), CD34(Abcam) and SMA(Abcam) antibodies for lymphatic vessels, blood vessels and smooth muscle cells respectively. Under general anesthesia, 50 µL fluorescent nanospheres (Invitrogen) were injected intracamerally in 3 sheep, with sacrifice 2 (n=2) and 4 (n=1) hours after the injection. Eyes were cryoprotected, serially sectioned and immunostained for a lymphatic endothelial marker (LYVE-1, Diagnostic Laboratories). Confocal laser microscopy was used to image ciliary body and capture images for 3-D construction (Microbrightfield Inc.).

Results: : In normal human eyes, numerous fine D2-40 positive lymphatic channels were observed in circular, radial and longitudinal portions of the ciliary muscle, stroma, and ciliary processes. D2-40 positive lymphatic channels surrounded many blood vessels in the ciliary body. In the normal sheep, numerous channels containing fluorescent nanospheres in the ciliary body were outlined by LVYE-1 immunoreactive lymphatic endothelial cells.

Conclusions: : A uveolymphatic pathway is described for the first time in the human and sheep ciliary body. The flow of aqueous humor into these channels indicates a new mechanism by which aqueous humor flows out of the eye, and if altered in glaucoma, is a possible novel therapeutic target.

Keywords: aqueous • outflow: ciliary muscle • ciliary body