Researchers at the University of Arizona and University of Tübingen have made a breakthrough in retinal implant technology that could help people who have lost their sight see more than just light and vague shapes.
Wolfgang Fink, an associate professor in the UA departments of electrical and computer engineering and biomedical engineering, is researching new implant design and methods of electrical stimulation of the retina that will enable retinal implants to produce much clearer images.
Fink conducted the research jointly with Erich Schmid, professor emeritus of theoretical atomic and nuclear physics at the University of Tübingen, Germany. Fink will present the team’s findings in San Diego during the Nov. 6-8, 2013 IEEE International Conference on Neural Engineering, organized by the Engineering in Medicine & Biology Society.
Only a handful of companies and research institutions worldwide are developing retinal implants, which stimulate surviving retinal cells in people who have lost their sight due to common degenerative diseases such as macular degeneration and retinitis pigmentosa. Implant patients can usually detect the presence of light, but the images they perceive are very low resolution.
“Current technologies and methods are far behind what can be done,” said Fink, who is working with Tech Launch Arizona to patent the new technology and license it to retinal implant developers.
The conference presentations – “Simultaneous vs. Sequential and Unipolar vs. Multipolar Stimulation in Retinal Prostheses” and “Electric Stimulation of Neurons and Neural Networks in Retinal Prostheses” – will reflect the team’s view that implants on the market don’t work, and will propose new methods for achieving higher resolution images so implant patients can see in greater detail.
The low-level visual acuity currently achievable, Fink said, enables implant patients to make out white stripes on a black computer screen, or to distinguish between white objects such as a cup and a plate on a black background in a darkened room. “But only if the patients are told in advance that they are to choose between a cup and a plate,” Fink said.
The level of restored vision the research team thinks is achievable, using its discoveries, is for an implant patient to be able to make out a bird flying in the sky. To accomplish that level of detail, the team’s novel method of electrical stimulation uses microsecond pulses, on-chip counter-electrodes, and controlled firing of electrodes to shape the electrical field.
The technology of retinal implants
Retinal implants consist of an array of electrodes that are activated – either by light entering the eye or by a signal from a camera mounted outside the eye – to emit electric fields, which in turn stimulate retinal cells that send signals to the brain.
In an attempt to achieve greater resolution, some companies are developing implants with more densely packed electrodes while maintaining the array’s same small footprint. Just adding more electrodes, however, is not the answer, Fink said, stressing that without the stimulation methodology he and Schmid propose, the vision achievable with hundreds or even thousands of electrodes would be no better than that achieved using tens of electrodes.
“Stimulation methodology is what achieves the improved vision, not electrode density,” Fink said.