An American doctor has been found to have Ebola in his eye - several months after he was treated for the condition.

And in a bizarre medical twist, the virus also changed his eye colour from blue to green.

Ian Crozier was diagnosed with the virus in September 2014 while working in Sierra Leone with the World Health Organization.

He was sent back to the US where he received treatment at Emory University Hospital's special Ebola unit in Atlanta, Georgia.

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Dr Crozier left the hospital in October when Ebola was no longer detected in his blood, according to the New England Journal of Medicine.

But two months later he developed an inflammation and very high blood pressure in his left eye, causing swelling and serious vision problems.

He returned to the same hospital where he had originally been treated, and an ophthalmologist, Dr Steven Yeh, removed some of the fluid and tested it for Ebola.

It did in fact contain the virus, but it was not present in his tears or the tissue around his eye.

Doctors believed he did not pose a risk of infecting other people, but Dr Yeh said the case shows that survivors of the deadly virus should be monitored for possible eye infection.

It has already known that the Ebola virus can persist in semen for several months after a patient is declared healthy.

The infection caused an inflammation of the inside of his eye, and it is not known how long this condition can last.

Besides the problems with his vision, Dr Crozier's iris changed colour, going from blue to green 10 days after the symptoms were first detected.

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After undergoing treatment with a variety of medicines, Dr Crozier began to recover his vision - although it is still not fully recovered - and his eye colour returned to normal.

Experts say cases of eye inflammation and problems with vision have been reported among survivors of Ebola in previous outbreaks, as well as among people with a virus known as Marburg, which is similar to Ebola

But such cases are rare, the medical journal said.

In the current outbreak, some cases of people with eye trouble have been reported among survivors of Ebola.

Dr John Fankhausser, chief of medicine at ELWA Hospital in Monrovia, Liberia, said chronic pain, headaches and eye trouble were the problems most often cited by 100-odd survivors who attended a meeting at that hospital.

Around 40 per cent suffered pain and inflammation in the eyes, he told The New York Times.

But the proportion of survivors who suffer these problems is still not known, the medical journal said.

The worst ever outbreak of Ebola began in southern Guinea in December 2013 before spreading to Liberia and Sierra Leone.

The death toll now exceeds 11,000, the World Health Organization reported this week, and the virus has infected more than 26,000 people since December 2013 in West Africa.

Now, the WHO has declared Liberia Ebola-free, 42 days - or twice the incubation period of the virus - after the last case.

- Daily Mail