The thick glasses Hillary Clinton has been wearing in public since returning from a concussion and blood clot last month are the result of lingering effects of her health problems, a Clinton aide confirms.
"She'll be wearing these glasses instead of her contacts for a period of time because of lingering issues stemming from her concussion," said spokesman Philippe Reines. "With them on she sees just fine."
During more than five hours of testimony before Congress Clinton could be seen wearing glasses that appeared to have a thick left lens with lines across it.
Reines did not specify what type of lens the secretary was wearing, but medical experts say a fresnel prism is common in cases like these. Fresnel prisms usually come in the form of a piece of thin, transparent plastic that can be adhered to existing lenses. The special grooves in these prisms change the way light enters the eye, making them useful in treating double vision.
PHOTOS: Hillary Clinton Through the Years
Dr. James Liu, director of the Center for Skull Base and Pituitary Surgery at the Neurological Institute of New Jersey, said that concussion and head injury can lead to blurred or double vision in some cases, and that this symptom can linger for a while during recovery.
"It is possible that blurred or double vision can last up to weeks and even months," he said. "This really depends on the severity of the head injury. In cases of concussions, these symptoms are usually temporary and eventually resolve with time."
The glasses did not seem to affect Clinton's demeanor during her testimony where she became emotional when talking about the deaths of Ambassador Chris Stevens and the three other Americans killed in the terror attack on the U.S. consulate in Benghazi, Libya. The secretary confidently answered questioned posed by senators and House representatives, and even sparred with some over her handling of the Benghazi crisis.
New York Magazine published an article showing a slideshow of Clinton adjusting her glasses during her testimony, with pithy comments about what her expressions meant.
Reines said that the secretary "got a kick out of the" article using her special glasses to see the slide show "crystal clear."