Eye tracking is a noninvasive technique that may help to assess two key physiologic signs of concussion, intracranial pressure (ICP) and ocular motility dysfunction, according to a study published online ahead of print June 2 in the Journal of Neurosurgery. This technique does not require a trained examiner, pupil dilation, imaging studies, or an invasive procedure such as lumbar or ventricular puncture, the authors noted.
“With these data, we are presenting a new application for eye-tracking technology, as well as a new mechanism for assessment of elevated ICP that is noninvasive, automatable, and could potentially be performed and analyzed remotely,” said Uzma Samadani, MD, PhD, Associate Professor of Neurosurgery at the University of Minnesota in Minneapolis, and colleagues.
The boundaries of normal and elevated intracranial pressure vary between patients, said the authors. People with elevated intracranial pressure can develop abnormalities in global cerebral functioning. Elevated ICP can also affect the function of cranial nerves, which may contribute to ocular dysmotility. Dr. Samadani and colleagues assessed the impact of elevated ICP on eye-tracking sessions performed while patients watched a short film clip.
Eligible participants ranged in age from 18 to 70, were admitted to the Bellevue Hospital neurosurgical intensive care unit in New York City with vision correctable to within 20/500 bilaterally, and had denied a history of ocular dysmotility. In addition, these patients were conscious and able to communicate and to provide an ophthalmologic, medical, and neurologic history, as well as medications, drugs, and alcohol consumed within 24 hours prior to eye tracking.
Awake patients who required placement of an ICP monitor for clinical purposes underwent eye tracking while watching a 220-second continuously playing video. The investigators recorded pupil position at 500 Hz and calculated metrics associated with each eye individually and both eyes together. In addition, the researchers performed linear regression with generalized estimating equations to test the association of eye-tracking metrics with changes in ICP.
The investigators performed eye tracking at ICP levels ranging from –3 mm Hg to 30 mm Hg in 23 patients (12 women, mean age 46.8) on 55 occasions. Eye-tracking measures correlating with cranial nerve function decreased linearly with increasing ICP.
Researchers also found that measures for cranial nerve VI were the most prominently affected. The area under the curve for eye-tracking metrics to discriminate between an ICP <12 mm Hg and one of ≥12 mm Hg was 0.798. To discriminate between an ICP <15 mm Hg and one of ≥15 mm Hg, the area under the curve was 0.833. Finally, to discriminate between an ICP <20 mm Hg and ≥20 mm Hg, the area under the curve was 0.889.
Overall, increasingly elevated ICP was associated with increasingly abnormal eye tracking detected while patients were watching the short film. The “technology has clinical applications for assessment of shunt malfunction, pseudotumor cerebri, concussion, and prevention of second-impact syndrome,” said Dr. Samadani and colleagues.
The major limitation of this study was the lack of continuous data in patients with higher ICP recordings, the authors said. Few patients with elevated ICP could open their eyes long enough to undergo eye tracking.
Kolecki R, Dammavalam V, Zahid A, et al. Elevated intracranial pressure and reversible eye-tracking changes detected while viewing a film clip. J Neurosurg. 2017 Jun 2 [Epub ahead of print].