Editor’s note: This article is Part 1 of 2. Here is Part 2.

Medical professionals are weighing in on Democratic presidential candidate Hillary Clinton’s eyes, which have appeared out of sync in videos of several recent speeches on the campaign trail.

Most recently, at a rally in Cleveland, Ohio on Friday, Clinton’s left eye appeared to turn more than her right when looking toward her right, a problem that seemed to have first emerged during a Philadelphia really last month.

The Ear and Balance Institute’s Dr. Gerald Gianoli, a neuro-otology surgeon who specializes in intracranial pressure, has not personally examined Clinton, but said it’s reasonable to draw some likely conclusions about the former secretary of state’s ongoing medical issues based on her eye activity in the videos and her known medical history.

“She has intermittent weakness of the left lateral rectus muscle” that pulls her left eye to the left, Gianoli said. “Due to this weakness, the left medal rectus pulls the eye too far to the right at times (because it is relatively stronger), especially when she looks to the right.

“This causes double vision,” he continued. “Mrs. Clinton first demonstrated this problem at the Benghazi hearings when she wore the Fresnel lens (prism lens) in her glasses on the left side. Fresnel lenses are used in patients who have problems with keeping both eyes looking at the same spot – it makes it easier for them to see one image as opposed to two images.”

Gianoli said the Clinton’s personal physician, Lisa Bardack, has previously confirmed the problem, though the cause of her continued issues with irregular eye movements hasn’t been shared with the public.

Gianoli offered several possible causes for the ongoing issues, but the most likely one is elevated intracranial pressure, or pressure inside of her skull.

“Mrs. Clinton is at greatly increased risk of elevated intracranial pressure and its consequences due to her lateral cerebral venous sinus thrombosis of 2012,” a condition that was acknowledged by Bardack in a statement on Clinton’s health released to the public, he said. “Among the most common consequences (include) visual problems, balance problems, headaches and brain fog.

“One of the most common visual problems is paralysis, partial paralysis or intermittent paralysis of the … cranial nerve with innervates the lateral rectus muscle. The paralysis is most commonly just on one side” and can be permanent or intermittent, Gianoli said, adding that Clinton is almost certainly continues to suffer from double vision.

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Other possibilities for the buggy eye movements are even more serious and include brain tumors, stroke, MS, brain damage from her concussion, ocular effects of thyroid disease, or several other neurological conditions, said Gianoli, who has conducted research with NASA scientists on non-invasive methods of measuring intracranial pressure.

Other physicians also believe Clinton’s eye problems are most likely tied to the venous sinus thrombosis that resulted from a concussion she suffered during a fall in late 2012.

Dr. John R. Coppedge, a surgical specialist from Texas with 37 years of experience, recently opined about Clinton’s issues for The Hill. Coppedge also has not personally examined Clinton, but offered his take based on several videos that exposed her eye issues, including a September 18 speech in Philadelphia and a press event at the airport the same day, as well as a press event on her plane following the third presidential debate and the October 21 speech in Cleveland.

Here are some examples from the Philly speech at Temple University:

Coppedge referenced Clinton’s disclosed 2012 concussion and State Department emails released by WikiLeaks referring to her “cracked head” as evidence that her transverse sinus thrombosis could be causing continued problems with intracranial pressure, resulting in her odd eye movements.

“The diagnosis that was announced publicly was that she had a thrombosed transverse venous sinus. That is a very serious problem,” Coppedge said. “But the word ‘sinus’ is confusing to the public since in this case it is a medical term meaning ‘vein,’ (and) has nothing to do with a person’s sinuses.

“There are two Transverse Sinuses. One on the right. One on the left. They are the major veins that drain blood from the brain and are situated between the … bottom of the brain and the base of the skull bone.”

There are many reasons for the veins to clot, but noted that Bardack confirmed Clinton has a history of Deep Venous Thrombosis and uses blood thinners.

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“With a thrombosed or clotted Transverse Sinus one gets increased intracranial pressure – swelling of the brain. That swelling puts pressure on the most exposed of the 12 cranial nerves, the sixth. In that case the lateral rectus muscle … is damaged,” he said.

“Unlike an injury where that nerve is cut in half causing total loss of function, the palsy or dysfunction cam be partial and even intermittent.”

Videos of Clinton’s recent speeches show the problem seems to be intermittent and results in what’s often called disconjugate gaze, or her eyes not moving together.

“If, as I suspect, Mrs. Clinton has lingering issues related to her traumatic brain injury that occurred in 2012, those might lead to other issues but there is no certainty of that,” Coppedge said. “Her condition could stabilize and unless something else occurred she could function at her current level. But if she has an underlying blood clotting problem that would probably surface again.”

Both doctors noted that the problem for the public is Clinton has not been entirely forthcoming about her ongoing medical issues, and sympathized with Bardack, who cannot release all of the facts about her patient without her consent.

“The only doctor in America who has said that (Clinton) is physically fit to serve as president is her private internist,” Coppedge said. “And that doctor is only allowed to release information about her patient that the patient agrees to be released (under penalty of law.)”

“What many in the public do not realize is that Dr. Bardack’s letters (detailing Clinton’s medical history and asserting she is physically fit to serve as president) cannot be taken as the whole truth,” Gianoli added. “She is constrained in her ability to say what is going on with Mrs. Clinton by both ethics and privacy laws. So, whatever is included in Dr. Bardack’s letter is only there if approved by Mrs. Clinton.”