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

To be able to show the blind again sounds like the things of miracles or even science fiction. And that has always been one of the biggest challenges for scientists. Diego Ghezzi, who holds the Medtronic Chair in Neuro-Engineering (LNE) at the EPFL School of Engineering, has put this issue as a research focus. Since 2015, he and his team have been developing a retinal implant that works with smart glasses with a camera and a microcomputer. “Our system is designed to give blind people a form of artificial vision by using electrodes to stimulate their retinal cells,” says Ghezzi.

Star-filled air

The camera embedded in the smart glasses takes photos in the wearer’s field of view and sends the data to a microcomputer placed in one of the glasses’ end caps. The microcomputer converts the data into light signals that are transmitted to the electrode 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 consists of dots of light that appear when the retinal cells are stimulated. Carriers, however, must learn to interpret the many dots of light to depict shapes and objects. ‘It’s like looking at stars in the night sky – you can learn to recognize specific constellations. Blind patients would see something similar with our system, ”says Ghezzi.

Running simulations, for now

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

Field of view and resolution

Two parameters are used to measure vision: field of view and resolution. The engineers therefore used the same two parameters to evaluate their system. The retinal implants they developed contain 10,500 electrodes, each serving to generate a dot of light. ‘We were not sure if it would be too many electrodes or not enough. We just had to find the right number so that the version does not become too difficult to make out. The dots must be far enough apart so that patients can distinguish two of them close to each other, but there must be enough of them to provide sufficient image resolution, ”says Ghezzi.

The engineers also had to make sure that each electrode could deliver a dot of light. Ghezzi explains: “We wanted to make sure that two electrodes do not stimulate the same part of the retina. Therefore, we performed electrophysiological tests that recorded the activity of retinal ganglion cells. And the results confirmed that each electrode does indeed activate a different part of the retina. ‘

The next step was to see if 10,500 light points provided a good resolution – and that’s where the virtual reality show came from. ‘Our simulations showed that the chosen number of dots and therefore electrode works well. To use more, the definition will not really bring benefits to patients, ”says Ghezzi.

The engineers also performed tests with a constant resolution but different face plane angles. ‘We started five degrees and opened the field to 45 degrees. We found that the saturation point is 35 degrees – the object remains stable outside that point, ”says Ghezzi. All these experiments have shown that the capacity of the system does not need to be further improved and that it is ready for clinical trials. But the team will have to wait a little longer before their technology can be implanted in real patients. For now, the restoration of vision in the field of science fiction remains.

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