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In some Ebola survivors, the virus leaves a unique scar at the back of the eye that can be seen long after they are cured of the disease, according to a new study.

Researchers analyzed information from 82 Ebola survivors in Sierra Leone and 105 people who lived in the area but never had Ebola. All participants took a vision test and had the back of their eyes examined with an ophthalmoscope. Among Ebola survivors, more than a year had passed, on average, between the time they were cured of the disease and the time of the eye exam.

When asked to read letters on an eye chart, the Ebola survivors tended to perform just as well as those who'd never had the disease, meaning their infection didn't seem affect their vision.

But about 15 percent of Ebola survivors had a unique scar on their retina — the light-sensitive tissue at the back of the eye. The people who had never contracted Ebola did not have this particular type of scar, the study found.

This scar, "often resembling a diamond or wedge shape, appears unique," the researchers said. The scar was next to the eye's optic disc, the spot where nerve fibers exit the eye to connect to the brain. This suggests that the Ebola virus enters the eye by traveling along the optic nerve, the researchers said.

Previous studies have found that up to 60 percent of Ebola survivors experience eye symptoms, including eye inflammation and temporary vision loss, but little is known about the patients' long-term vision outcomes, the researchers said.

About 7 percent of the Ebola survivors in the new study had white cataracts, or cloudy areas in the lens of the eye that can affect vision. In contrast, no white cataracts were found in the participants who'd never had Ebola, the researchers said.

However, it's not clear whether Ebola survivors could safely have surgery to remove cataracts, because there is concern that the virus can linger in the eye and might pose a risk to doctors preforming the surgery.

But in the new study, the researchers tested the eye fluid of two Ebola survivors with cataracts, and the fluid tested negative for the virus. This finding suggests that Ebola does not necessarily remain in eye fluid in survivors with cataracts, and that in some patients, cataract surgery could be performed safely, the researchers said.

The study is published in the July issue of the journal Emerging Infectious Diseases.