Many of the world’s leading causes of irreversible blindness, such as glaucoma and age-related macular degeneration, have a common problem: fluid, waste, and inflammatory debris build up at the back of the eye.
But for decades, scientists lacked a clear understanding of how the eye removes this waste.
A new study from the University of British Columbia and the University of Toronto has identified what appears to be a missing piece of the puzzle: a previously unknown waste elimination system deep in the back of the eye. A hidden circulatory pathway called the posterior ocular lymph outflow tract (POLO pathway) provides a pathway for fluids and waste products to leave the eye and enter the body’s lymphatic system.
The retina is one of the most metabolically active parts of the body, constantly producing byproducts that must be removed. The discovery helps explain how the eye flushes out this waste and promises to change the way we think about and treat various eye conditions. ”
Dr. Neil Gupta, Professor and Head of UBC Department of Ophthalmology and Visual Sciences
Foundation for future treatments
Diseases such as glaucoma, macular degeneration, and retinal disease are all associated with fluid accumulation, metabolic waste accumulation, and tissue stress and inflammation. Age-related macular degeneration alone affects approximately 2.5 million Canadians.
The discovery of the POLO pathway suggests the existence of a natural system responsible for the removal of this substance, opening new opportunities to exploit this system in the treatment of disease.
This provides an entirely new framework for understanding these diseases and potential targets for treatment. The question now is how this purification system can be enhanced or utilized to treat or prevent disease. ”
Dr. Neil Gupta, Professor and Head of UBC Department of Ophthalmology and Visual Sciences
hidden in plain sight
For more than a century, it was thought that the eye did not have a lymphatic system. The lymphatic system is present in nearly every other organ and helps regulate body fluids, remove waste products, and support immune function.
Dr. Gupta and Dr. Yeni Yucel, professor and director of ophthalmic pathology at the University of Toronto, began challenging that idea in 2009 when they discovered a lymph-related drainage pathway in the front of the eye called the “uveal lymph” pathway. However, the secrets behind the eye, which are the root cause of many diseases that lead to blindness, remain largely unknown.
“The retina is responsible for vision, and many of the most serious vision-loss diseases occur here,” Dr. Yucel said. “It’s important to understand how this part of the eye maintains a balanced environment and flow of substances.”
To uncover the POLO pathway, the team used advanced imaging in mice that combines MRI, near-infrared fluorescence, and microscopic analysis. They introduced fluorescent tracer molecules into the thin space at the back of the eye and tracked their movements in real time.
This allowed them to identify small lymph vessels within the choroid, a thin layer beneath the retina. The fluid drained from the back of the eye into the surrounding orbital tissue and within minutes reached nearby lymph nodes that connect the eye to the broader lymphatic system.
“The choroid was thought to be devoid of lymphatic vessels, so the research team used multiple techniques to demonstrate the presence and function of lymphatic vessels,” added Dr. Yucel, a pathologist and scientist at St. Michael’s Hospital. “We were surprised to see a direct route for fluid to leave the eye and connect to the lymphatic system. This suggests that there is an active clearance pathway deep within the eye that may play an important role in removing fluid, proteins, and inflammatory substances that accumulate during disease.”
Further research is needed to understand how the human lymphatic pathway functions and how it can be targeted for therapy.
But researchers say it could one day lead to improved drug delivery to the back of the eye, new treatments that increase fluid clearance, and deeper insights into how pressure, inflammation and fluid dynamics contribute to vision loss.
“This is a fundamental discovery that shows that the eye is not as closed a system as previously thought,” Dr. Gupta said. “It gives us new maps, new mechanics, and a new set of questions to explore.”
This research today Translational Vision Science & Technology.
sauce:
University of British Columbia
Reference magazines:
Sauntarajan, B. Others. (2026). Identification and mapping of the posterior ocular lymphatic outflow (POLO) pathway through the choroidal lymphatics. Translational Vision Science & Technology. DOI: 10.1167/tvst.15.7.23. https://tvst.arvojournals.org/article.aspx?articleid=2818359
