Retinal implants equipped with 10,500 electrodes to provide artificial vision to the blind

Being able to make blind people see again sounds like miracles or even science fiction. And it has always been one of the biggest challenges for scientists. Diego Ghezzi, who holds the Medtronic chair in Neuroengineering (LNE) at the EPFL School of Engineering, made this edition a focus of research. Since 2015, he and his team have developed a retinal implant that works with smart glasses equipped with a camera and a microcomputer. “Our system was designed to give blind people a form of artificial vision, using electrodes to stimulate their retinal cells,” says Ghezzi.

Starry sky

The camera built into the smart glasses captures images in the user’s field of view and sends the data to a microcomputer placed at one end of the glasses. The microcomputer turns the data into light signals that are transmitted to the electrodes in the retinal implant. The electrodes stimulate the retina so that the user sees a simplified black and white version of the image. This simplified version is made up of points of light that appear when the cells of the retina are stimulated. However, users must learn to interpret the many points of light to distinguish shapes and objects. “It’s like when you look at the stars in the night sky – you can learn to recognize specific constellations. Blind patients would see something similar in our system, ”says Ghezzi.

Running simulations, for now

The only problem is that the system has not yet been tested on humans. The research team must first be sure of its results. “We are not yet authorized to implant our device in human patients, as it takes time to obtain medical approval. But we created a process to test it virtually – a kind of workaround, ”says Ghezzi. More specifically, engineers developed a virtual reality program that can simulate what patients would see with the implants. Their findings have just been published in Communication Materials.

Field of view and resolution

Two parameters are used to measure vision: field of view and resolution. Engineers, therefore, used these same two parameters to evaluate their system. The retinal implants they developed contain 10,500 electrodes, with each serving to generate a point of light. “We were not sure if that would be too many electrodes or not enough. We had to find the right number so that the reproduced image would not become too difficult to decipher. The points must be far enough away for patients to be able to distinguish two of them close to each other, but there must be enough to provide sufficient image resolution, ”says Ghezzi.

Engineers also needed to make sure that each electrode could reliably produce a spot of light. Ghezzi explains: “We wanted to make sure that two electrodes did not stimulate the same part of the retina. Then, we performed electrophysiological tests that involved recording the activity of the retinal ganglion cells. And the results confirmed that each electrode actually activates a different part of the retina. “

The next step was to see if 10,500 points of light provide good enough resolution – and that’s where the virtual reality program came in. “Our simulations showed that the chosen number of points and, therefore, of electrodes, works well. Using nothing else would have no real benefit for patients in terms of definition, ”says Ghezzi.

Engineers also performed tests at constant resolution, but at different angles of field of view. “We started at five degrees and opened the field up to 45 degrees. We found that the saturation point is 35 degrees – the object remains stable beyond that point, ”says Ghezzi. All of these experiments demonstrated that the system’s capacity does not need to be improved any more and that it is ready for clinical testing. But the team will have to wait a little longer before their technology can be deployed in real patients. For now, restoring vision remains in the realm of science fiction.

Reference: March 5, 2021, Communication Materials.
DOI: 10.1038 / s43246-021-00133-2