Researchers from the University of British Columbia and the University of Toronto have discovered a previously unknown drainage route in mice called the posterior ocular lymphatic outflow, or POLO pathway. This hidden cleanup system carries fluid and waste from the back of the eye into the lymphatic network.
Scientists have uncovered a cleanup system at the back of the eye, revealing a pathway that allows fluid and waste to escape into the body’s lymphatic system. The finding challenges assumptions about how the eye functions and could eventually provide therapeutic targets for major causes of permanent vision loss, including glaucoma and age-related macular degeneration.
Mapping the POLO Pathway Behind the Retina
A research team from the University of British Columbia (UBC) and the University of Toronto identified the unrecognized drainage route, designated the posterior ocular lymphatic outflow or POLO pathway. The system appears to channel fluid and metabolic waste away from the back of the eye and into lymphatic vessels, helping maintain fluid balance and support immune defenses.
To trace how fluid exits the back of the eye, the researchers used a combination of imaging techniques in mice. These methods included magnetic resonance imaging, near-infrared fluorescence imaging, and microscopic examination. By placing fluorescent tracer molecules into a narrow space at the back of the eye, the team followed the fluid’s movement as it traveled into tiny lymphatic vessels located within the choroid—a thin, blood vessel-rich layer beneath the retina where lymphatic vessels had not previously been established. Within minutes, the tracers reached nearby lymph nodes, demonstrating a functional connection to the body’s lymphatic system.
Newly Discovered Pathway Drains Fluid from the Eye
For over 100 years, scientists generally believed that the eye lacked the lymphatic drainage systems found in nearly every other organ. This idea began to change in 2009, when Dr. Gupta and Dr. Yeni Yücel identified a lymphatic-related drainage route in the front of the eye. The discovery of the POLO pathway now extends that to the rear of the organ.
Major retinal disorders such as glaucoma and age-related macular degeneration—a condition affecting approximately 2.5 million Canadians—are associated with the accumulation of fluid, cellular waste, tissue stress, and inflammation. Until now, researchers have struggled to explain exactly how this sensitive region removes unwanted substances.
The findings were published in the scientific journal Translational Vision Science & Technology. Support for the research was provided by the Canadian Institutes of Health Research, the Glaucoma Research Society of Canada, the Henry Farrugia Ophthalmology Research Fund, the Canadian Space Agency, the Dorothy Pitts Chair, the Stephen M. Drance Chair, the Thor and Nicky Eaton Research Fund, and the Canada Foundation for Innovation Leaders Opportunity Fund.
