By Deborah Borfitz 

October 15, 2024 | A mechanical engineer at the University of Houston is seeking physician collaborators with a research need for a small but sensitive wearable eye-tracking system to provide continuous data on human brain activity. The need was suggested by a survey of the literature, which found that a shortage of data coming from devices used in supervised clinical settings was resulting in inconclusive correlations study after study, according to associate professor Jae-Hyun Ryou, Ph.D.  

Spotting the need, his lab got to work on a set of three wearable sensors, each smaller than a penny, that attach comfortably to the upper, mid and lower temple to enable easy, ongoing measurements and monitoring of eyeball movements. The flexible piezoelectric eye movement sensor array (F-PEMSA) was described in an article that was published recently in Advanced Healthcare Materials (DOI: 10.1002/adhm.202303581). 

This is one of many different types of sensors Ryou’s group is developing for personal healthcare applications, including a pulse wave velocity sensor for assessing vascular changes and arterial stiffness and a cortisol (stress hormone) sensor for monitor conditions affecting the adrenal and pituitary glands. As engineers, they jump to build and embrace promising new technology, Ryou says. 

This is much less the case with clinical groups, which tend to be more cautious, he adds. Unless new technology means a “real breakthrough” for their practice, they’ll stick to what they got. 

But if they’re studying brain activity, they are likely to realize the value of continuous monitoring data, Ryou says. “If we can provide that from our sensors, they’ll be motivated to find us.” 

Ryou and his team still have some work to do, most immediately turn their proof-of-concept sensors into full-scale sensors that can wirelessly transmit signals to a base station such as a smartphone or iPad. They could then be applied as a complete monitoring system in clinical trials with physician partners. 

That will of course take funding, which the researchers are currently trying to secure. Commercializing the sensing technology could easily take another three to five years, he says.  

Clinical Possibilities

The eyes, being an anatomical extension of the brain, are a window into a vital but otherwise inaccessible organ. The objective of Ryou and his colleagues is to improve upon existing eye-tracking systems that have three key shortcomings—they deliver insufficient amounts of data due to their weak outputs, are bulky with multiple electrodes affixed to the face and neck, and the ones required for eye tracking studies can cost tens of thousands of dollars. 

Typically, these research-grade systems involve some sort of head gear and optical methods to measure eye movement by reflecting light from the eye and analyzing the changes in reflection, he says. But they capture data intermittently, providing only an objective glimpse into brain function and cognition. It can therefore be difficult to confidently support a hypothesis where eye movement is the yardstick, including experiments where kids are being diagnosed with attention-deficit/hyperactivity disorder or investigators are monitoring the symptomatic progression of older adults with Alzheimer’s or Parkinson’s disease. 

The clinical possibilities with F-PEMSA are vast, since ophthalmological assessments of eye blinking patterns have been used for the early diagnosis of multiple neurological disorders, says Ryou. Ocular movements have also been strongly linked to various brain disorders, and motor neurons in the brain have been associated with autism.  

F-PEMSA leverages the phenomenon of piezoelectricity, which means any mechanical change (e.g., bending or vibrating) in the solid material comprising the sensors will put out a voltage. It’s the same effect used by quartz clocks to generate a series of electrical pulses that mark time, Ryou explains. 

The tiny size of these sensors, which can be easily worn on the temple area of the face to take continuous measurements, is the system’s best feature, he adds. The sensors can quickly detect changes in the movement of muscles that control the eyelid and eyeballs in all possible directions and at the micrometer level.  

One other big benefit of the sensor element is that, unlike many of the piezoelectric materials his group is working on, the thin-film transducers are safe, says Ryou. For most of the wearable concepts explored up to now, the sensors have been made partially of lead and therefore would be quite toxic to the human body if they were to break out of their protective packaging. “Our [latest] sensor is very, very inert.”