The first presidential debate of 2016 is being held Monday, September 26th, and everything about the presidential candidates' professional and personal lives will continue to be scrutinized, including their health. During a recent speech in Philadelphia, Hillary Clinton, whose health has been under a particularly harsh spotlight, exhibited abnormal eye movements. Some health experts suggest they could be a sign of an underlying health issue, though no proof of a disorder has been uncovered.

In footage from Clinton’s speech, her eyes do not appear to move in the same direction at the same time. According to John R. Coppedge, a general surgeon from Texas who recently wrote an article for The Hill on the subject, this behavior is indicative of a problem with the left sixth cranial nerve. Coppedge has never personally examined Clinton.

Although there are a number of possible causes for such an impairment, Coppedge suggests that Clinton’s strange eye movement is likely the result of an intermittent lateral rectus palsy which was caused by damage to or pressure on her sixth cranial nerve.

The lateral rectus muscle rotates the eye away from the nose, and when it is weak, the eye can cross inward toward the nose. According to the American Association for Pediatric Ophthalmology and Strabismus, lateral rectus palsy can have a number of causes, ranging from stroke and tumors, to migraine headaches and birth defects.

The condition could be caused by a number of Clinton's already publicly known health issues. For example, in late 2012 she suffered a concussion after falling and hitting her head. During her examination, doctors found a transverse sinus thrombosis, or blood clot in the large vein that wraps around her brain. Both these events could put pressure on her sixth cranial nerve and be the cause of her erratic eye movement. However, this is speculation, and may have nothing to do with her eye movement issues.

It is worth noting that Coppedge does not have expertise in ophthalmology, a branch of medicine dedicated to eye care. In addition, according to the AAPOS, many times the cause of lateral rectus palsy is never determined despite extensive investigation, so it may be that we will never truly know the reason behind what appears to be strange eye behavior, but which may actually be normal and healthy.

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