By John R. Coppedge, MD, FACS is a general surgeon from Texas, originally posted on The Hill

In 2014 Conan O'Brien did a spoof of Hillary Clinton's interview with Diane Sawyer about her lack of lingering health issues following her 2012 concussion. In an obviously photoshopped version Clinton's eyes are made to oscillate crazily.

It was a very funny piece. Now, it may not seem so funny.

Hillary Clinton exhibited abnormal eye movements during her recent speech in Philadelphia and they were not photoshopped.

Her eyes did not always move in the same direction at the same time. It appears that she has a problem with her left sixth cranial nerve. That nerve serves only one function and that is to make the lateral rectus muscle contract. That muscle turns the eye in the direction away from the midline.

It comes out of the base of the brain and runs along the floor of the skull, immediately beneath the brain before coursing upward to the eye. Dysfunction of that muscle causes the striking picture of the eyes not aiming in the same direction and causes the patient to suffer double vision.

Like all things medical, there is a long list of potential causes but in my opinion the most likely one, based on Clinton's known medical history is an intermittent lateral rectus palsy caused by damage to or pressure on her sixth cranial nerve.

It is known that she suffered a traumatic brain injury in late 2012 when she fell and struck her head. What is also known is that she was diagnosed with a transverse sinus thrombosis — blood clot in the major vein at the base of the brain. Almost all patients with a transverse sinus thrombosis suffer swelling of the brain and increased intracranial pressure. Most have headaches, balance issues and visual disturbances — all of which Clinton was reported to have following that event.

Clinton's physician reported that she was placed on Coumadin (a blood thinner) to dissolve the blood clot. Actually, that is incorrect, because Coumadin has no effect on an existing clot. It serves only to decrease the chance of further clotting occurring Clinton's physician has also reported that on follow up exam, the clot had resolved. That is surprising since the majority of such clots do not dissolve. The way it was documented that the clot had resolved has not been reported.

If, as is statistically likely, Clinton's transverse sinus is still blocked, she would still have increased pressure and swelling and decreased blood flow to her brain. That swelling would place pressure on the exposed portion of the sixth cranial nerve at the base of her brain, explaining the apparent lateral rectus palsy. And such a deficit can be partial and/or intermittent.

Additionally, when patients who have decreased intracranial blood flow becoming volume depleted (dehydrated) or have a drop in blood pressure loss of consciousness can occur. That could explain her witnessed collapse in New York City on 9/11.

One thing that is taught early in medical school is that a patient's history, physical exam, signs and symptoms should usually lead to a single diagnosis.

Crudely put "when you itch, it is probably not lice and fleas but one or the other." More professionally put, in most cases the patient's symptoms can be explained by one unifying diagnosis, not a constellation of disparate ones. The admittedly speculative scenario I propose is an attempt to understand and rationally explain what is going on, based on known facts and the observable signs exhibited by Clinton.

Having previously written about this, I once again suggest that she undergo an independent neurologic exam and have proper studies to determine whether or not she still has a blood clot at the base of her brain, swelling of the brain, increased intracranial pressure and whether or not her 2012 traumatic brain injury was accompanied by a skull fracture with or without bleeding around or in the brain itself and if there are any residual areas of scarring of the brain.

Critics will rightly point out that I have not examined Clinton. They will point out that I am not ophthalmologist or a neurologist. But I am a physician and the concepts discussed above are taught to every medical student early in their education. Her traumatic brain injury, transverse sinus thrombosis, subsequent symptoms, falling, passing out and now the obvious problem with eye movement are all fact, not speculation.

It would be very helpful if Clinton agreed to an independent exam and to have the questions raised here answered. It is too important not to get this right.