Closed-eye imaging allows monitoring of wakefulness, consciousness and pain under conditions of insensibility

New technology allows researchers, for the first time, to monitor changes in pupil size and gaze direction behind closed eyes using noncontact infrared imaging. In the future, tracking changes in pupil size will help identify wakefulness during sleep, anesthesia, and intensive care, track sedation depth, detect seizures and nightmares, and recognize pain or reactivity that may occur after trauma and in intensive care units. The researchers predict that this technology has great potential to become an important tool in clinical care.

The discovery was made by a team of researchers from Tel Aviv University led by PhD student Omer Ben Barak-Dror, under the joint supervision of Prof. Yuval Nir of the Department of Physiology at the Faculty of Medical and Health Sciences, Sagol School of Neuroscience and the Department of Biomedical Engineering, and Prof. Israel Gannot of the Department of Biomedical Engineering. Other members of the team are Dr. Michal Tepper, Dr. Barak Hadad, Dr. Hani Barhum and David Haggiag.

The research was published in the journal Communication medicine.

Professor Nir notes that “it is often said that the eyes are the windows to the soul.” Indeed, the size of the pupils is constantly changing, dilating or contracting to regulate the amount of light coming in, while providing valuable clinical information. We all know that our pupils constrict in bright light and widen in darkness. But that is only one reason why pupils change size. They also dilate when we are stimulated, for example when we react to a sudden event or when we feel pain. In such cases, our autonomic nervous system serves as an alarm, preparing us to act.

Tracking pupil size and eye movements can be crucial in many clinical situations. However, until now, this has been limited to open-eye scenarios. There was no method to do this when the eyes were closed.

The new research describes an innovative technology that combines shortwave infrared (SWIR) imaging with deep learning algorithms to perform non-contact pupillometry and eye tracking behind closed eyelids.

“To establish and validate our technology, we focused on the pupillary light reflex (PLR) when the pupil constricts in response to a sudden flash of light and then dilates again to return to normal. This is a basic reflex that occurs symmetrically in both eyes in healthy people. We performed experiments to test our technology on the closed eye while comparing the results to data obtained with the open eye,” said Omer Ben Barak-Dror, lead author of the study at Tel Aviv University.

Professors Nir and Gannot observe: “Our method successfully tracks the precise dynamics of the pupillary light reflex under closed-eye conditions, revealing changes in pupil size after each light flash in individual subjects, and also accurately estimates where the gaze is directed, with an accuracy of a few degrees. The system operates at wavelengths where light has its maximum penetration depth into biological tissues, and by analyzing the data using deep learning algorithms, we can go beyond what is typically possible with standard near-infrared imaging methods.”

Dr. Tepper adds that information collected using contactless continuous monitoring is a critical part of a patient’s electronic medical record (EMR) and helps make decisions about optimal medical treatment.

The researchers conclude: “Our technology, supported by a patent application, paves the way for the development of devices with wide-ranging clinical and commercial applications in areas ranging from sleep medicine to monitoring the level of sedation and intraoperative consciousness in anesthesia, to the assessment of pain and responsiveness in unresponsive patients or in neurological and trauma intensive care units.”