Scientists at the University of British Columbia and the University of Toronto have identified a previously unknown drainage system at the back of the eye. Called the posterior ocular lymphatic outflow, or POLO pathway, it appears to move fluid and metabolic waste from the retina and choroid into the body's lymphatic network. The findings, published from work in mice, challenge a belief held for more than a century that the eye has no lymphatic connections of this kind.
The research team traced fluorescent tracers injected into the space behind the retina using MRI, near-infrared imaging, and microscopy. They found tiny lymphatic vessels in the choroid, the blood-vessel-rich layer beneath the retina. This follows the same researchers' 2009 discovery of a lymphatic-related drainage route in the front of the eye, but the back of the eye had remained largely unexplored until now.
Because fluid buildup and waste accumulation are linked to glaucoma, age-related macular degeneration, and other causes of permanent vision loss, the finding gives scientists a new framework for investigating these diseases. The next step, according to the researchers, is to determine whether the pathway can be strengthened or exploited to protect vision.