Many locked-in syndrome patients communicate with an alphabet chart, blinking to indicate their choices as a caretaker points to each letter. Others use devices that measure eye movement patterns representing "yes" or "no." Completely locked-in patients who aren't able to move their eyes at will may be able to use systems that translate brain activity into speech, although 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 who lack motor control — and decodes them into yes or no responses, potentially offering an easier alternative for locked-in syndrome 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 math problems.
Since this happens automatically, patients don't 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's also relatively inexpensive, consisting of just a camera and laptop.
In a trial described 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 math problem onscreen.
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 information to a laptop. A software program immediately 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. The researchers 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% 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 couldn't answer the questions independently, he was able to solve math problems if the researchers pointed at them. The system translated these responses with more than 80% accuracy, suggesting that it could also serve as a diagnostic tool to assess a patient's state of consciousness, the researchers wrote.
Within the next two years, the researchers hope to finish fine-tuning the EyeSeeCam so that it works better for severe locked-in syndrome cases, Einhauser said. They also plan to make the device less cumbersome. It will eventually resemble a small webcam that can be hooked up to a laptop.
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.
Mark Delargy, a physician at Ireland's National Rehabilitation Hospital, agreed. Although the study controlled for lighting changes and other environmental factors that can affect pupil size, internal variables, such as emotional state, are more difficult to control. Anxiety and pain can cause the pupils to dilate, for example.
But identifying these emotions in locked-in patients is tricky. "They won't tell you any new information," said Delargy, who was not part of the study. "You have to devise a question to enable them to tell you."
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. Now that they've "provided the proof of principle," testing the system on completely locked-in patients is "definitely on the agenda," he said.
Even if pupil size does accurately reflect yes or no responses, the study tested only the EyeSeeCam, so it's undetermined whether it offers an advantage over existing systems, Birbaumer said.
Still, the device "has potential," Delargy said. "This is one of the greatest hopes for rehabilitation of locked-in patients and for the opportunity to give a voice to people who have lost it."