There were dozens of photographs taken of Secretary of State Hillary Clinton recording her emotions as she gave congressional testimonies regarding the Sept. 11, 2012, attacks in Libya. But medical experts have taken a closer look at the photographs and have found they reveal something else about her current health — Clinton might have double vision.

Hillary Clinton Wearing Fresnel Prism on Glasses Suggesting Double Vision

Medical experts have said the lines that can been seen on Clinton’s left eyeglass lens is a Fresnel prism, which can help prevent double vision. (Photo: Chip Somodevilla/Getty Images)

According to the New York Daily News, Director of Fromer Eye Centers Dr. Mark Fromer noticed in closeup pictures of Clinton, it appears she is wearing an addition to her glasses called a Fresnel prism.

“If she’s wearing a Fresnel prism, then she has double vision without it,” Fromer told the Daily News.

The Daily News reported another New York City-based eye doctor saying that double vision was the only reason there could be for wearing spectacles with a Fresnel prism.

Hillary Clinton Wearing Fresnel Prism on Glasses Suggesting Double Vision

(Photo: SAUL LOEB/AFP/Getty Images)

Fresnel-Prism.com describes the 3M Press-On Optics as for patients post-cataract surgery who are bed ridden with low vision and also those experiencing other muscle deficiencies. An article in MedScape News explained that the Fresnel prism works by using “a concentric set of prismatic rings with the face of each ring having the prismatic power or curvature of the lens element it replaces.”

Hillary Clinton Wearing Fresnel Prism on Glasses Suggesting Double Vision

US Secretary of State Hillary Clinton testifies before the Senate Foreign Relations Committee on the September 11, 2012 attack on the US mission in Benghazi, Libya, during a hearing on Capitol Hill in Washington, DC, on January 23. (Photo: SAUL LOEB/AFP/Getty Images)

As Fromer put it, the addition to the glasses “helps bring images into focus.”

In December, Clinton fainted and suffered a concussion, after which she didn’t return the office for several weeks. During this time, her health was examined by doctors who found a blood clot in the space between her skull and brain, but it was not predicted to result in neurological damage and she was expected to fully recovery. Clinton left the hospital after treatment for the clot Jan. 2 and returned to work Jan. 7.

The Daily News reported a spokesman saying that Clinton’s recent health conditions are the reason for her wearing the stick-on addition to her glasses, but he did not state their purpose.