A bedside device that expertly analyzes eye movements could one day save lives by helping doctors determine whether stroke is the cause of a patient’s disabling, severe, continuous dizziness, or a more benign condition like vertigo.
A small “proof of concept” study reported online this week in the journal Stroke shows how the device was able to diagnose stroke with 100% accuracy.
The electronic device is a small, portable, video-oculography machine that detects minute eye movements that are difficult for most physicians to notice.
Study leader David Newman-Toker, an associate professor of neurology and otolaryngology at the Johns Hopkins University School of Medicine in Baltimore, Maryland in the US, says in a statement:
“Using this device can directly predict who has had a stroke and who has not.”
“We’re spending hundreds of millions of dollars a year on expensive stroke work-ups that are unnecessary, and probably missing the chance to save tens of thousands of lives because we aren’t properly diagnosing their dizziness or vertigo as stroke symptoms,” he explains.
There is a series of three eye movement tests that specialists can do to find out if the cause of a patient’s dizziness is due to stroke or a less serious condition like vertigo, which is linked to a disturbance in the inner ear.
Our sense of balance comes from the vestibular system in the inner ear working with the visual system to keep what we are looking at in focus when the head is moving.
The eye movement tests are in effect a stress test for the balance system, and have been shown to be extremely accurate. They are “nearly perfect, and even better than immediate MRI,” says Newman-Toker, who led a study published in 2009 that first showed how a one-minute eye movement exam performed at the bedside worked better than an MRI to distinguish new strokes.
The test is called a horizontal head impulse test and requires the patient to keep looking at a target on the wall while a trained doctor or technician moves the patient’s head from side to side and looks carefully to see if they are making the rapid, corrective side to side eye movements that indicate vertigo or some other benign condition is the cause of the dizziness as opposed to stroke.
But, as the authors explain in their background information to the study, to make an accurate diagnosis, the doctor or technician carrying out the eye movement test requires a high level of expertise, one that is not routinely available in emergency departments.
So they decided to investigate the feasibility of replacing this expertise with a standard test “through the novel application of a portable video-oculography device measuring vestibular physiology in real time”.
Newman-Toker likens the device to using an ECG (electrocardiogram) to rule out heart attack in patients with chest pain.
For their small study, the researchers tested how well the video-oculography machine was able to detect the minute eye movements that are difficult even for the most skilled physician to spot.
The device comes with a set of goggles that look like swimming goggles incorporating a webcam and accelerometer. The goggles connect to a laptop allowing a continuous picture of the eye to be viewed and recorded via the webcam. A program in the computer analyzes eye movements by following how the pupils change position, and the accelerometer measures the speed of the movement.
To test the device, the researchers recruited 12 patients admitted to emergency departments at The Johns Hopkins Hospital and the University of Illinois College of Medicine at Peoria whose symptoms included severe dizziness, vomiting, difficulty walking and intolerance to head motion.
The device diagnosed six patients with stroke and six with a benign condition. MRI later confirmed all 12 diagnoses.
Newman-Toker says if these results are confirmed in additional larger studies, the device could one day be used in all hospital emergency departments to “virtually eliminate deaths from misdiagnosis and save a lot of time and money”.
The device he and his team used is one that is already approved for use in balance clinics outside the US but has not yet gained approval in the US.
It was made by a company called GN Otometrics, who had no involvement in the study, apart from loaning their machine to the team.
Making an accurate diagnosis of stroke in patients presenting with severe dizziness is difficult.
Newman-Toker estimates that some 4 million patients visit emergency departments every year in the US complaining of vertigo or dizziness, and at least half a million of these are at high risk for stroke.
While the most common causes are problems in the inner ear, many emergency room doctors struggle to tell the difference between these and stroke, so they often rely on brain imaging, usually a CT scan, to make the diagnosis.
Around 40% of patients presenting with dizziness are sent for CT scans.
This is an expensive and not very accurate method of making such a diagnosis, says Newman-Toker, explaining that CT scans miss more than 80% of acute strokes in the brainstem and cerebellum.
The only definitive way to rule out stroke is the MRI scan, but this equipment isn’t readily available in many emergency departments and rural hospitals. The costs of an MRI scan is about four times that of a CT scan.
And even MRI scans can miss between 10% and 20% of acute strokes in the brainstem and cerebellum in the first 48 hours after symptoms begin, says Newman-Toker, who reckons the new device would probably prevent around 100,000 misdiagnoses a year.
Overlooked strokes lead to delayed or missed treatments, resulting in some 20,000 to 30,000 preventable deaths or disabilities in the US a year, he adds.
Grants from the the Swiss National Science Foundation, the Agency for Healthcare Research and Quality, and the National Institutes of Health’s National Center for Research Resources and National Eye Institute helped to finance the study.
Written by Catharine Paddock PhD