Retinal implant shines light on artificial vision

This is the claim of a team led by Diego Ghezzi, who have been developing the system since 2015.

"Our system is designed to give blind people a form of artificial vision by using electrodes to stimulate their retinal cells," said Ghezzi, who holds the Medtronic Chair in Neuroengineering (LNE) at EPFL's School of Engineering in Lausanne, Switzerland.

Intraneural electrode stimulates light sensation for the blind

The camera embedded in the smart glasses captures images in the wearer's field of vision, and sends the data to a microcomputer placed in one of the eyeglasses' end-pieces. The microcomputer turns the data into light signals which are transmitted to electrodes in the retinal implant. The electrodes then stimulate the retina in such a way that the wearer sees a simplified, black-and-white version of the image. This simplified version is made up of dots of light that appear when the retinal cells are stimulated. However, wearers must learn to interpret the many dots of light in order to make out shapes and objects.

"It's like when you look at stars in the night sky - you can learn to recognize specific constellations. Blind patients would see something similar with our system," Ghezzi said in a statement.

The system has not been tested on humans but the team has developed a virtual reality program that can simulate what patients would see with the implants. Their findings have been published in Communication Materials.

Field of vision and resolution are two parameters used to measure vision and the engineers used these to evaluate their system. Their retinal implants contain 10,500 electrodes, with each one generating a dot of light. "We weren't sure if this would be too many electrodes or not enough. We had to find just the right number so that the reproduced image doesn't become too hard to make out. The dots have to be far enough apart that patients can distinguish two of them close to each other, but there has to be enough of them to provide sufficient image resolution," said Ghezzi.

The team also had to avoid two electrodes stimulating the same part of the retina. “So we carried out electrophysiological tests that involved recording the activity of retinal ganglion cells,” said Ghezzi. “And the results confirmed that each electrode does indeed activate a different part of the retina."

According to EPFL, the next step was to check whether 10,500 light dots provide good enough resolution, which required the introduction of a virtual reality program. "Our simulations showed that the chosen number of dots, and therefore of electrodes, works well. Using any more wouldn't deliver any real benefits to patients in terms of definition," said Ghezzi.

The engineers also performed tests at constant resolution but different field-of-vision angles, starting at five degrees and widening the field to 45 degrees. “We found that the saturation point is 35 degrees - the object remains stable beyond that point," said Ghezzi.

The team’s experiments demonstrated that the capacity of the retinal implant does not need to be improved any further, and that the next stage will involve clinical trials.