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Optic Nerve Stimulation Developed as Visual Prosthetic

OpticSeline array

OpticSeline array (Markus Ding, EPFL)

20 Aug. 2019. Engineers in Europe developed an electronic device that connects to and stimulates the optic nerve, producing simple visual patterns in lab animals. A team from L’Ecole Polytechnique Fédérale de Lausanne or EPFL in Switzerland and Sant’Anna School of Advanced Studies in Pisa, Italy describe the device in yesterday’s issue of the journal Nature Biomedical Engineering (paid subscription required).

Researchers in EPFL’s Center for Neuroprosthetics, led by biomedical engineering professors Diego Ghezzi and Silvestro Micera, are seeking more treatment options for people with permanent blindness, resulting from diseases or trauma to the eye. World Health Organization estimates 36 million people worldwide are totally blind, with an aging population continually adding to that number.

Up to now, most electronic devices to treat vision impairment or blindness target the retina, the sensory layer lining the back of the eyeball with photoreceptor cells that convert light into signals carried by the optic nerve into the visual cortex of the brain for interpretation. These devices, however, require a functioning retina. People with retinitis pigmentosa, a progressive genetic disorder, lose that functioning retina, leading to total blindness in some cases.

Stimulating the optic nerve — in effect, bypassing the retina — can produce phosphenes, sensations of light produced by bio-photons from different stimuli, such as rubbing a closed eye. Other researchers tried before electronically stimulating the optic nerve, but with little success.

“Back then, they used cuff nerve electrodes,” says Ghezzi in an EPFL statement. “The problem is that these electrodes are rigid and they move around, so the electrical stimulation of the nerve fibers is unstable. The patients had a difficult time interpreting the stimulation, because they kept on seeing something different.”

Ghezzi, Micera, and colleagues took a different approach, integrating electrodes into the optic nerve, known as intraneural electrodes. These electrode connections, say the researchers, are more stable than cuff electrodes and more likely to produce reliable results. The team devised an array of 12 intraneural electrodes called OpticSeline that addresses different nerve fibers in the optic nerve.

The researchers tested OpticSeline with anaesthetized rabbits. The team sent electric currents through the electrodes to the optic nerves of the rabbits, and measured activity in the visual cortex of their brains. A complex algorithm helped the researchers interpret the recorded brain activity, called electrocorticography. The researchers report selective stimulation of optic nerve in the rabbits produced specific and unique visual patterns.

With 12 electrodes, the OpticSeline array in the study proved the concept with rabbits, but for humans, the array will likely need 48 to 60 electrodes. It may not be able to completely restore sight to people with blindness, say the researchers, but it could offer limited visual functioning.

“For now,” notes Ghezzi, “we know that intraneural stimulation has the potential to provide informative visual patterns. It will take feedback from patients in future clinical trials in order to fine-tune those patterns. From a purely technological perspective, we could do clinical trials tomorrow.”

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