Doctors in Toronto are setting up a network to track cases of a mysterious eye disease that has shut down one of the city's busiest cataract surgery centres.

Toxic anterior segment syndrome, or TASS, causes an inflammation in the eye's interior. The disease has appeared at clinics across North America in the last two years.

TASS often resolves quickly with anti-inflammatory treatment, but in severe cases can lead to torn or detached retinas, a form of glaucoma and vision loss.

Scarborough Hospital in Toronto's east end cancelled all cataract surgeries last week. About 30 patients developed TASS following their operations, said the hospital's president, Dr. Hugh Scott. The cases have not been severe, he said.

"Not knowing why it came, not knowing why it leaves, it's truly a mysterious syndrome," Scott told CBC News on Wednesday.

In TASS, the eye reacts to something foreign such as bacteria or a chemical, and the cases may be dismissed as an infection, said Dr. David Wong, a University of Toronto ophthalmologist and a retinal surgeon.

Bacteria and viruses do not cause the disease, which occurs when toxins enter the anterior segment of the eye. The segment is located between the lens and the cornea — the area targeted in cataract surgeries.

Cleaning protocol on scrutiny

Surgical materials come in sterilized, but instruments have to be washed. Suspicion often falls on detergents used to clean the instruments, since chemicals in the packaging may be enough to trigger TASS, Wong said.

"That's an indication that something has happened in the protocol of cleaning,"  agreed Dr. Henry Edelhauser, an Atlanta-based eye expert who is part of a task force that investigated an earlier outbreak. "That's usually what we have found in the past."

Antibiotics or preservatives may also be to blame.

TASS has affected about 137 eye centres across North America in the past 18 months. It is often difficult to determine the source. 

The Scarborough Hospital is bringing in an independent research firm to investigate the TASS outbreak.

The cataract surgery centre will likely reopen in about a week, Scott said. Surgeons at the hospital perform about 5,000 operations each year.