The Eyes: Windows to Our Health

It’s said that the eyes are windows to the soul. But to Professors Yeni Yucel and Neeru Gupta and their research team, the eyes are windows to our health.

In 2009, Yucel and his team found that contrary to popular belief, the human eye has a lymphatic system. This system is responsible for clearing fluid and waste out of tissues. The inability to clear fluid from the eye causes a buildup of pressure, and pressure is the main cause of glaucoma.

“Since then, our contribution has been to look at the implications of this completely new system for eye health, vision, and disease,” said Yucel, a professor of Opthalmology and Laboratory Medicine and Pathobiology, and a pathologist at St. Michael’s Hospital.

Most recently, in a paper published in early June, the team of researchers found that in vivo photoacoustic imaging – a technique that allows for very high-resolution imaging of a live model – can be used to measure fluid movement from inside the eye to the neck’s lymph nodes. This novel work proved that fluid from the eye drains at least in part to the larger lymphatic system, tying the eye to the larger fluid flow in the body.

Another study in late 2017 revealed a previously unknown pathway through which cerebrospinal fluid – the water around the brain – enters the optic nerve. This has added to the body of knowledge around the glymphatic system – the waste clearance pathway of the central nervous system – and has contributed a new perspective to glaucoma research.

Glaucoma is one of the world’s leading causes of irreversible blindness. Often undetected in its onset, once a patient receives the diagnosis, progressive vision loss is inevitable, although it can be slowed with treatments to lower pressure in the eye. 

“We really don’t know what causes glaucoma,” says Gupta, also a professor of Opthalmology and Laboratory Medicine and Pathobiology, a clinician-scientist at St. Michael's and co-primary investigator of these studies. “We know there’s a problem with the drainage system of the eye and fluids not getting out. These discoveries open up a brand new window – now we can look at whether the problem in glaucoma is a lack of waste clearing, or an issue with this glymphatic system.”

The team's discoveries will also help test the efficacy of new medications for diseases such as glaucoma, and look at other targets to treat the eye.

“Everything we do has the patient at the centre,” says Gupta, director of the Glaucoma Unit at St. Michael’s, and a member of the Board of Directors of the World Glaucoma Association. 

“There would be no excitement in any of this research if we didn’t feel it was deeply connected to the patients who sit in our exam rooms every day.”