Scientists have developed technology to restore some sight to the blind. Their method bypasses the eyeball and instead stimulates the optic nerve with a new type of intraneural electrode called OpticSELINE. The results were reported today in Nature Biomedical Engineering.
“We believe that intraneural stimulation can be a valuable solution for several neuroprosthetic devices for sensory and motor function restoration,” says co–senior author Silvestro Micera of EPFL.
Blindness affects an estimated 39 million people in the world. Many factors can induce blindness, such as genetics, retinal detachment, trauma, stroke, glaucoma, cataract, inflammation, and infection. But restoring sight is not straightforward. A handful of strategies have been proposed, such as retinal or brain implants, but these are either narrowly applicable or high risk. The new solution increases applicability since the optic nerve and the pathway to the brain are often still intact in blind individuals.
Previous attempts to stimulate the optic nerve provided inconclusive results. “Back then, they used cuff nerve electrodes,” says co–senior author Diego Ghezzi of EPFL. “The problem is that these electrodes are rigid and they move around, so the electrical stimulation of the nerve fibers becomes unstable. The patients had a difficult time interpreting the stimulation, because they kept on seeing something different. Moreover, they probably have limited selectivity because they recruited superficial fibers.”
Intraneural electrodes may indeed be the answer for providing rich visual information to the subjects. They are also stable and less likely to move around once implanted in a subject, according to the scientists.
The researchers engineered the OpticSELINE, an array of 12 electrodes, which they used to deliver electric current to the optic nerve of rabbits. They then measured the brain’s activity in the visual cortex and decoded the cortical signals using an elaborate algorithm. Their results showed that each stimulating electrode induces a specific and unique pattern of cortical activation, suggesting that intraneural stimulation of the optic nerve is selective and informative.
As a preliminary study, the visual perception behind these cortical patterns remains unknown. According to Ghezzi, “it will take feedback from patients in future clinical trials in order to fine-tune those patterns.”
With current electrode technology, a human OpticSELINE could consist of 48–60 electrodes. This limited number of electrodes is not sufficient to restore sight entirely. But these limited visual signals could be engineered to provide a visual aid for daily living.
Image: OpticSELINE electrode array for intraneural stimulation of the optic nerve, developed in the Translational Neural Engineering Lab, and used in preliminary studies. Image courtesy of EPFL / Markus Ding, 2019.