Researchers found a drainage route behind the mouse eye that scientists long believed did not exist

Researchers at the University of British Columbia and the University of Toronto report a previously unknown drainage route at the back of the eye, which they call the posterior ocular lymphatic outflow pathway, or POLO. The experiments were conducted in mice.

The study appeared in Translational Vision Science and Technology, volume 15, issue 7, 2026. Its listed authors include Babishaa Sauntharrajan, Neeru Gupta, Xun Zhou, Ekim Gümeler, Greg Stanisz, Wilfred W. Lam, Margaret Koletar and Yeni H. Yücel, according to the ScienceDaily record, which gives the paper’s reference as article 23 and the DOI 10.1167/tvst.15.7.23.

A belief that lasted more than a century

The drainage route in the mouse eye is notable because, per the UBC release, the eye was thought for more than a century to lack a lymphatic system. Scientists long believed such a route did not exist in the eye at all. According to a ScienceDaily summary of the work, the route appears to carry fluid and waste from the rear of the retina into the body’s lymphatic network.

The finding matters because of what it contradicts. As ScienceDaily puts it, “For over 100 years, scientists generally believed” that the eye lacks the lymphatic drainage found in nearly every other organ. Dr. Neeru Gupta, professor and head of the department of ophthalmology and visual sciences at the University of British Columbia, calls the result “a foundational discovery that shows the eye is not as closed a system” as previously thought, in the university’s announcement of the study.

Gupta and Dr. Yeni Yücel, professor and director of ophthalmic pathology at the University of Toronto and a pathologist-scientist at St. Michael’s Hospital, had been pressing on that assumption for years. In 2009 they reported a drainage route at the front of the eye and named it the uveolymphatic pathway, according to the same release. A paper indexed in PubMed under the heading Discovery of lymphatics in the human eye and implications belongs to that literature on lymphatics in the eye.

The back of the eye, where many blinding diseases begin, had remained largely unstudied until the POLO work, the UBC announcement says.

How the team traced the route

The team placed fluorescent tracer molecules into a narrow space at the back of the mouse eye and followed their movement using magnetic resonance imaging, near-infrared fluorescence imaging and microscopic examination. Because lymphatic vessels in the choroid, the blood vessel-rich layer beneath the retina, were not thought to exist, the researchers used several techniques to confirm both that the vessels were present and that they worked, per the UBC release.

The results, as summarized by ScienceDaily, were direct. Tiny lymphatic vessels turned up in the choroid, a region where such vessels had not previously been established. Fluid moved from the back of the eye into the surrounding orbital tissues, and the tracers reached nearby lymph nodes within minutes, linking the eye to the wider lymphatic system.

Yücel said in the announcement that the team had not expected to find so direct a route for fluid to leave the eye and join the lymphatic system. Gupta described the stakes in terms of workload, noting that “The retina is one of the most metabolically active parts of the body,” and adding that the discovery “helps explain how the eye flushes this waste.”

Earlier work on the front of the eye gives a sense of how lymphatic anatomy can vary within a single organ. A 2020 study in JCI Insight led by Young-Kwon Hong’s group examined mice, rats and human donor cornea rims and found that lymphatics on the eye’s surface were denser on the nasal side and drained a tracer faster there. That research concerns the outer, front surface, not the choroid, and it is a separate line of work from the POLO paper.

What the finding could mean for disease, and what it cannot yet

The researchers tie the discovery to conditions in which fluid, waste and inflammation build up. Glaucoma, age-related macular degeneration and other retinal disorders all involve some combination of those problems, according to the ScienceDaily account. Age-related macular degeneration alone “affects approximately 2.5 million Canadians,” it states. Possible applications raised by the team include therapies that boost fluid clearance and better delivery of drugs to deep structures of the eye.

Those applications are framed as future possibilities, and the limits are plain. The work was done in mice, so it has not been shown in people. Whether the pathway changes in disease, and whether it can be modified safely, are listed as unknown. Gupta herself put it as a question, asking how the cleanup system might be enhanced or exploited to treat or even prevent disease. She also described the paper as offering “a new map, a new mechanism and a new set of questions to explore.”

Funding for the study came from 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, according to ScienceDaily. The open question that the authors leave on the table is whether a human eye has the same route, and the published paper is where any test of that would first have to be reported.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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