The Zika virus has been found in fluid around the eyes of some patients, shedding new light on how the virus affects healthy adults, according to a study published today in Journal for the American Medical Association Ophthalmology.

The eyes of six patients infected in South America were swabbed by researchers from the Guangdong Provincial Institute of Public Health in China. When they tested their eye fluids, they found Zika virus RNA.

"Here we have some evidence when the adult is infected, it would appear that highly specialized neural tissue is infected," Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical School, told ABC News. He said the next step would be examining if the virus caused any vision problems.

The virus was known to cause severe eye damage in developing fetuses. Babies born with microcephaly have exhibited symptoms of eye infection, including lesions in the eye. But it was unclear if the development of microcephaly or the Zika virus itself led to the lesions.

Until now, it was also unclear if the virus was present in the eyes of adults.

Schaffner said researchers are still learning the many ways the Zika virus, which usually causes mild symptoms including fever, fatigue and pink eye, can affect adults and how it can remain in different parts of the body.

Despite being discovered in 1947, the Zika virus was not widely studied until the recent outbreak that started in Brazil last year and that has been linked to birth defects.

The virus has been found to cause severe birth defects in developing fetuses, including microcephaly, characterized by a small head, as well as other brain and eye defects.