Vision loss ranks first among the threatening diseases. No wonder, since it provides up to eighty percent of the information about the outside world. Now two new implants should at least shed some light into the darkness.
According to the WHO, there are 36 million people around the world who are blind. In Germany around 150,000 people share this fate. Most suffer from age-related macular degeneration (AMD) or from retinitis pigmentosa, involving the irreversible destruction of the sensory cells in the retina.
For that reason, researchers have spent many years attempting to regain rudimentary visual function by transplanting retinal tissue – grown from stem cells – in animal trials. But it is unlikely that this method will be used on people within the next decade. Electronic solutions in the form of implants offer better prospects for partially restoring eyesight.
Scientists from the Swiss Federal Institute of Technology in Lausanne (EPFL) recently presented a retina implant that stimulates the retinal cells electrically with electrodes. While up to now this method had only been able to achieve a field of vision of around 20 degrees, the EPFL variant has more than doubled this to 46 degrees. 40 degrees is considered “normal” sight.
Current retinal implants consist of an electrode grid that is wired to a pair of glasses, a camera and a microcomputer. In this method, the camera sends the images captured in the field of vision to the computer, which converts them into electrical signals and forwards them to the electrodes. These then generate a point of light by stimulating the retinal ganglion cells. This results in a black and white pattern made of many individual points of light, which the patient must learn to interpret in order to ultimately recognize objects.
The EPFL implant works in a similar way, but doesn’t use wires. This is because the researchers replaced the electrodes with 10,500 photovoltaic pixels, which require no external energy source, and the light captured by the camera no longer needs to be converted into electrical signals. This way, it was possible to significantly increase the number of light points, which improves the field of vision and the quality of the image.
Initial tests with isolated animal eyes have already been successful. In the next step, the EPFL implant needs to demonstrate its qualities in in vivo studies.
Alongside retinal prostheses, scientists are also working on cortical implants. These address the central illnesses of the visual system caused by the likes of diabetes mellitus. Planted directly in the cortex (section of the brain), they stimulate neuronal functions with electrical impulses, evoking visual impressions.
In the international “I See” project, for example, a miniature camera converts images into signal patterns that are transmitted to implants in the brain. There, they control the areas of the brain that are responsible for processing visual information.
Until now, these cortical visual prostheses with electrical pulses mostly only generated bright, round points of light. If these are increased, the simultaneous stimulation with several electrodes will quickly lead to very large injected currents, overloading the visual system.
However, the prostheses could be significantly improved by taking into account the activation of the cerebral cortex that is already there and adapting the stimulation to the information coding in the brain. Future brain-to-computer interfaces should therefore learn the “language of the brain” with advanced data analysis methods and adjust the right time to gently couple the desired visual impression to the pre-activation of the brain.
While cochlear implants are already the medical standard for deaf people, projects for the visually impaired such as “I See” are still a vision, but they promise to improve the quality of life of those affected in the future.
Nature communications: Design and validation of a foldable and photovoltaic wide-field epiretinal prosthesis