A New York ophthalmologist told FoxNews.com that special glasses former Secretary of State Hillary Clinton was seen wearing last year are used to treat double vision, which is sometimes caused by severe head trauma.

Dr. Marc Werner explained the purpose of the Fresnel prism eyeglasses, like the ones Clinton wore, amid questions about the potential presidential candidate's health. The subject was raised after Karl Rove commented on her time in and out of the hospital in December 2012.

"In order to see one object, your eyes need to be pointed in the same direction. If your eyes are misaligned, one way to optically align them is to put a prism ... on your glasses," Werner said.

In late 2012, Clinton was suffering from a stomach virus when she fell at her home, struck her head and endured a concussion, according to her representatives. Doctors later discovered a blood clot behind her right ear. Werner says severe head trauma could have caused double vision and Clinton's need for Fresnel prism glasses.

"Any issue which raises intracranial pressure can damage one of the nerves which moves the eye around, and if it damages one of the nerves, your eyes will be misaligned -- maybe temporarily, maybe more permanently," Werner said.

Fox News analyst and former George W. Bush administration adviser Karl Rove recently defended comments he reportedly made saying Clinton's hospitalization would be an issue should she run for president in 2016.

"This was a serious deal. She basically was out of action," Rove said Tuesday. "She spends over a month fighting this. ...And they're not particularly forthcoming."

Clinton's representatives, and husband, have defended her, saying she's "100 percent." Bill Clinton said earlier this week there's "nothing to" the health questions -- though at the same time, he revealed her recovery took about six months, which is much longer than the State Department had indicated.

When asked what he might look for given the chance to see Clinton's medical records, Dr. Werner said he would want to examine imaging studies.

"I would like to know what the results of any imaging studies were and the cause of why someone needed Fresnel," Werner said. "There are lots of different causes, anything from Myasthenia to Multiple Sclerosis to maybe a blood clot, these are all possible causes, but all we know is that she was using a Fresnel prism and therefore had double vision."