This text is part of the special Research section
Researchers at the University of Sherbrooke are developing a technology that could allow some blind people to recover part of their vision. Part of the solution could fit on a microchip the size of a grain of oats implanted in the retina.
People with retinitis pigmentosa begin to have trouble seeing in dim light and lose peripheral vision, which makes them feel like they’re seeing through a tunnel. This genetic disease causes a progressive degeneration of the photosensitive cells of the retina, until the person becomes blind, or almost. The disease affects 1 in 4000 people.
“The retina is the part of the eye that captures the image and converts it into electrical signals, which are sent to the brain via the optic nerve,” explains William Lemaire, doctoral candidate in electrical engineering at the University of Sherbrooke. The idea is to replace the function of these cells with a retinal implant, an electronic device that plays the same role. »
The retina is made up of several layers of cells, continues the doctoral student. If cones and rods no longer work in people with retinitis pigmentosa, bipolar and ganglion cells on the surface of the retina can still communicate with the optic nerve. It is with these cells that the implant will communicate information through electrical microdischarges.
There are already retinal prostheses that allow patients to recognize silhouettes or door frames, but vision remains very approximate. Under the leadership of Professor Réjean Fontaine, a dozen engineers and student-researchers have been working for seven years to develop a new generation of more efficient artificial retinas, which could make it possible to make a giant leap in the treatment of diseases. degenerative diseases of the retina.
The retinal implant, which sends images to the brain through the optic nerve, functions in a way like a Web camera which sends images to a computer by a USB cable, popularizes William Lemaire. The patient will wear glasses equipped with a camera that captures the images and sends them to the implant by modulating the intensity of infrared light. Attached to the retina, a 5 millimeter by 4 millimeter electronic chip receives infrared light codes and translates them into electrical signals. These electrical stimulations are sent to the functional cells of the retina through nearly 300 electrodes. If the first generation devices must be connected to small electrical cables ensuring their energy supply, the chip developed by the Sherbrooke team has a photovoltaic cell powered by a light beam from the glasses.
The great challenges of nanotechnology
To improve the resolution of the image perceived by the blind person, the researchers are trying to multiply the number of electrodes on the chip. These correspond in some way to the number of pixels of the created image. For now, these electrodes are separated by a distance of 150 microns — the diameter of a hair. The Sherbrooke team wants to reduce this gap to 10 microns, a real technical feat.
“The challenge is that these kinds of microsystems are too small to be handled by standard devices,” observes Réjean Fontaine, specialist in nanoelectronics and biomedical technologies at the University of Sherbrooke. We are developing techniques to be able to make collages, microassemblies, soldering and laser cutting on small circuits, we are recognized in Canada for that,” observes the researcher, who insists on the multidisciplinarity of his team.
“That’s sort of the key to success,” he says. There are people who work on signal processing, others on integrated circuits, assembly or on artificial neural networks which, later, will be implemented [sur la puce] he explains, adding that this multidisciplinary experience also prepares students for complex projects in the job market. The Quebec team also collaborates with researchers from the University of Melbourne, Australia, who specialize in certain materials at the heart of the implant, such as carbon fibers and diamonds.
Their task is all the more difficult as there is still a lot to learn about the functioning of the cells of the retina. Are the latter excited or inhibited by the current from the electrodes? What is their response to different current intensities? For the moment, the microchanges are difficult to observe by patients, who only perceive blurred spots.
“We sail blindly”, illustrates Mr. Fontaine. To overcome this problem, his team has developed a chip that will “read” the electrical responses in the eye and thus better calibrate the action of the electrodes. Implanted in the brain, this same chip could also be useful for predicting epileptic seizures 24 hours in advance.
Researchers at the University of Sherbrooke still have a lot on their plate before a possible commercialization of this artificial retina. However, the device will not restore normal sight to people with retinitis pigmentosa, but rather improve their quality of life, warns Réjean Fontaine. “The important thing for patients is that they can see their loved ones,” he says. And that is priceless. »