A team involving USC researchers working on a device to restore sight recently reported their first findings on how an eye interprets different types of electrical stimuli.
The research, conducted by scientists at the Keck School of Medicine, the Doheny Eye Institute and Second Sight Medical Products Inc., was presented at the Society of Neuroscience’s annual meeting in Washington, D.C., on Nov. 13.
Research team members are developing and testing an implanted retinal prosthesis that sends electrical signals through the eye to the brain. Their hope: that the prosthesis may someday help those who have lost their sight due to diseases such as retinitis pigmentosa and macular degeneration.
In their recent research presentation, the group reported how people who had become blind due to a loss of photoreceptors perceived electrical stimuli given through the retinal implant. Since the nervous system normally uses chemical signaling, not electrical impulses, to communicate information within the retina, it was not clear how the retina’s different cell types would interpret direct electrical stimulation.
“We’re trying to understand how the eye and brain processes electrical information, and how they translate that signal into perception,” said Alan Horsager, a graduate student in the Keck School Department of Ophthalmology who presented the research at the meeting.
Horsager studied three blind subjects who were implanted with a retinal prosthesis, a tiny square of 16 electrodes. The electrodes were stimulated through a visual processing unit that sends the signals wirelessly through a magnetic coupling device.
The researchers electrically stimulated their subjects’ blind eyes and then asked the subjects to perform behavioral tests to establish when they saw a flash of light, and what these flashes looked like. The shape and duration of the electrical signals were varied so as to determine which types of electrical impulses might work best to create suitable visual perceptions.
They found that varying interactions take place across different cell types in the retina, depending on what types of electrical pulses are used.
For example, some retinal cells are stimulated more by one type of electrical pulse than another, and some cells can prolong or dampen the response of neighboring cells. Understanding these interactions is an important key to developing a useful retinal prosthesis, Horsager said.
“If we know what types of retinal cells respond to various electrical signals, we can be more selective in what we stimulate,” Horsager says. “Our ultimate goal is to provide continuous input to the eye, to make it possible to see a constant, moving image.”