Scientists studying the Zika outbreak in Brazil are becoming increasingly concerned the virus may cause eye damage in babies.

Stanford University researchers found abnormal bleeding and lesions in the eyes of three infant boys whose mothers had caught Zika while pregnant.

They want any babies known to be affected by Zika to have eye checks.

The journal of Ophthalmology findings followanother recent study that saw similar eye problems in Zika babies.

The disease is already known to cause a serious baby brain defect called microcephaly.

What is not clear is whether eye problems might be a complication of this rather than the Zika infection itself. Either is possible.

All of the three infants the researchers from Stanford and the University of Sao Paulo examined also had microcephaly.

The eye damage they found in the baby boys was to the light-sensitive layer of tissue at the back of the eye, called the retina.

There was abnormal blood vessel growth, bleeding and torpedo-shaped lesions.

Researcher Dr Darius Moshfeghi said the next step was to determine the root cause – Zika or microcephaly – to better understand which infants would need eye checks.

“To begin with it’s probably sensible just to screen babies with microcephaly,” he said.

“But if it turns out that Zika can cause these eye problems independently, then we would need to screen all infants of infected mothers.”

He said some of the eye abnormalities would resolve or be treatable, but others could cause lasting, irreversible damage to vision.

With no vaccine or treatment, pregnant women have been advised to cover up to protect themselves against the biting mosquitoes that carry Zika.

More than 60 countries and territories now have continuing Zika transmission.