Some Brazilian babies born with birth defects linked to Zika virus also have severe eye problems in addition to brain damage, doctors report.
The doctors found eye damage in more than one-third of babies they studied in December at a hospital in Salvador, Brazil's third largest city. The babies all were born with a rare condition known as microcephaly, which results in head and brain abnormalities.
The findings, detailed yesterday in JAMA Ophthalmology, provide the strongest evidence to date that the mosquito-borne virus is also now linked to potentially threatening vision problems, researchers said.
Lee Jampol, a professor of ophthalmology at Northwestern University's Feinberg School of Medicine, said the lesions found in the babies' retinas could have far-reaching impacts for families trying to care for the infants and the next generation.
"We know these babies are at risk for real problems with their vision," said Jampol, who also co-authored a commentary on the study. "The main message here is that it's likely that Zika is going to spread further, and you're going to have to pay attention to these babies," he said.
Experts have raised the possibility of the virus and an association with other neurologic problems. Yale epidemiologist Albert Ko, who is also researching the potential effects of the virus in Brazilian newborns, said researchers are also seeing some babies with microcephaly who have impaired hearing.
In Brazil, the epicentre of the outbreak in the Americas, Zika has been linked to a surge of microcephaly cases. CDC officials have said the association between the virus and microcephaly has become stronger. So, too, has a link between Zika and Guillain-Barré syndrome, which can lead to paralysis in adults. Several South American countries have identified cases of that rare condition.
The JAMA study involved 29 infants and their mothers who were examined at Roberto Santos General Hospital in Salvador, Brazil. Twenty-three of the mothers said they suspected a Zika infection during pregnancy, most of them in the first trimester. Of the 29 infants born with microcephaly, 10 of them, or more than a third, had "severe ocular abnormalities," the study found.
The most common problem affected their retinas.
"Imagine you have a big TV screen," said Rubens Belfort Jr., a study co-author in an interview. "That's the retina. In these babies born with microcephaly, many areas of the screen will never work because they have dark spots."
Some of the babies are still being cared for in intensive-care units, said Belfort, a physician at the Federal University of São Paulo, Brazil. In one case, the mother was 16, the father was 17 and their baby has microcephaly and severe damage to both retinas.
"The baby will probably be blind, maybe deaf, and have other cognitive issues," Belfort said. "It's a big problem. What is going to happen to the mother? The damage goes much beyond the eye or the child."
Belfort and researchers found the linkage between the virus and eye damage in two earlier studies examining different populations of babies. The researchers have ruled out other possible causes of microcephaly, such as infections with rubella or toxoplasmosis.
The possiblity of causes other than Zika for the microcephaly and eye damage are "very small," Belfort said. "When you start to see the same changes in different populations, it makes it probable."
In Brazil, researchers are planning to follow all the babies as they grow to monitor their vision. They also plan to examine more patients -- babies with microcephaly and babies with normal-sized heads -- in other parts of Brazil's northeast, hardest hit by the virus.