A research team at the University of Toronto has uncovered the existence of a distinct lymphatic system in the ciliary body that might provide new ways to treat glaucoma, according to a study in the November issue of Experimental Eye Research.

Using electron microscopy and three-dimensional reconstruction, the researchers suggest that aqueous fluid and other waste materials created by ocular tissues exit the eye, in part, through these lymphatic channels. Previous glaucoma research indicated the eye lacked lymphatic circulation and that aqueous humor chiefly exited the eye through the trabecular meshwork. In the rest of the body, lymphatic circulation is responsible for pumping fluid and waste out of tissues. The lymphatic circulation, distinct from blood circulation, carries extra water, proteins and antigens through lymphatic vessels to lymph nodes and then to the blood stream.

The discovery of a lymphatic circulation in the eye challenges the idea that the eye is an immune-privileged site due to the lack of lymphatics, and it has major implications for understanding eye inflammation and eye tumor spread, among other eye disorders. It is now evident that “this uveolymphatic circulation plays a role in the clearance of fluid from the eye, making it highly relevant to glaucoma,” says author Neeru Gupta, M.D., Ph.D. “This discovery is exciting because it means that we can focus on innovative treatment strategies for patients with glaucoma by specifically targeting this new circulation system to lower eye pressure.”

“This is a very interesting finding and clearly has great potential to improve understanding of ocular fluid dynamics, metastatic tumor spread and inflammatory eye disease,” says Michael Sullivan-Mee, O.D., of the VA Medical Center in Albuquerque, N.M., commenting on the study. “If the lymphatic pathway can be exploited to improve IOP control, it must first be determined what role the lymphatics already play in uveoscleral outflow.”

Currently, the specifics of uveoscleral outflow are not well understood, “and it is possible that lymphatics already participate in that outflow,” Dr. Sullivan-Mee says. “Of course, if it is found that uveoscleral outflow already relies heavily on lymphatic drainage, then that pathway is already being exploited for outflow by the prostaglandin class of medications.”  

Yücel YH, Johnston MG, Ly T, et al. Identification of lymphatics in the ciliary body of the human eye: a novel “uveolymphatic” outflow pathway. Exp Eye Res. 2009 Nov;89(5):810-9.