Eye opener for brain-damaged patients
New EyeSeeCam system measures changes in pupil size, decoding them into 'yes' or 'no' responses to help 'locked-in' people communicate
"Locked in" patients with brain damage that has left them mute and motionless may be able to communicate with a system that measures the size of their pupils, a new study has found.
Individuals suffering from locked-in syndrome have lost motor control, but remain aware and alert. The rare condition usually results when damage occurs to the brain stem, which controls motor function. Stroke, traumatic brain injury and amyotrophic lateral sclerosis (also known as Lou Gehrig's disease) can cause locked-in syndrome.
Many patients with locked-in syndrome communicate with an alphabet chart, blinking to indicate their choices as a caretaker points to a letter. Others use devices that measure eye movement patterns representing "yes" or "no".
Locked-in patients who cannot move their eyes at will may be able to use systems that translate brain activity into speech, but these often require surgical implantation and special training.
A new system called the EyeSeeCam measures changes in pupil size that happen involuntarily - even in people unable to blink - and decodes them into "yes" or "no" responses, potentially offering an easier alternative for such patients, including completely locked-in individuals.
In the 1960s, researchers discovered that pupil size can be used to measure mental effort. The bigger a person's pupils, the harder his or her brain is working. Neuroscientists used these findings to develop the EyeSeeCam, which takes advantage of how people's pupils dilate when they try to solve maths problems.
Since this happens automatically, patients did not need to be trained to use the EyeSeeCam, said Wolfgang Einhauser, a neurophysicist at Philipp University of Marburg in Germany, who helped develop the device.
It is also relatively inexpensive, consisting of a camera and laptop computer.
In a trial described on Monday in the journal Current Biology, Einhauser and his colleagues asked patients 15 simple questions, such as "Are you 20 years old?" After each question, the computer presented the patient with "yes" or "no" options, while showing a maths problem.
Patients solved only the problem associated with their response, and the mental effort caused their pupils to dilate. An infrared camera mounted to a headpiece measured their pupil size over time and sent the data to a laptop.
A software program translated the measurements into responses based on when they peaked. When the researchers tested the EyeSeeCam on six healthy individuals, it decoded their pupil sizes into accurate answers almost every time. They saw similar results in three out of seven locked-in syndrome patients, almost all of whom could manage small head movements. With some slight adjustments, it correctly translated the pupil dilations of two additional patients more than 70 per cent of the time.
"We found that quite remarkable," Einhauser said.
Only one out of four patients with more severe locked-in syndrome - marked by more widespread brain damage - finished the trial, and his answers were no more accurate than guessing.
The researchers also tested the EyeSeeCam on a minimally conscious patient with severely impaired cognitive ability. Although he could not answer the questions independently, he was able to solve maths problems if the researchers pointed at them.
Although completely locked-in patients stand to benefit most from the EyeSeeCam, the trial participants still had control over their eye movements, said Niels Birbaumer, a neurophysicist at the University of Tuebingen in Germany who was not involved in the study. As a result, "we have no idea whether pupil size" accurately reflects yes or no responses, he said.
But the EyeSeeCam's success in the minimally conscious participant has made the researchers confident that pupil dilation can serve as a means of communication, Einhauser said.