Vision restoration: From prostheses to genetic-based brain-machine interfaces.

Visual restoration is the major challenge for brain-machine interfaces because vision requires perception of images containing a high number of pixels that have to be presented at a high refresh rate. Classically, visual prostheses were made of electrode arrays with electrode numbers varying from very few to more than thousands. They demonstrated the feasibility of restoring useful vision either at the retinal level in diseases with photoreceptor degeneration or at the cortical level following optic nerve atrophy. Patients can find contrasted objects on a table and read letters or even words. However, they cannot recognize faces. The revolution of biotechnology and gene therapy is offering novel strategies to stimulate neuronal circuits without direct contact to the tissue as with electrodes. Optogenetic therapy is rendering neurons sensitive to light, thanks to a microbial opsin while sonogenetic therapy generates neurons sensitive to ultrasound waves. While optogenetic therapy has already been validated in patients recovering some vision following photoreceptor degeneration, sonogenetic therapy has only been evaluated in rodents at the cortical level. These novel brain-machine interfaces offer novel perspectives for restoring vision in blind patients, but their applications may easily extend to other handicaps or neurologic diseases.