Researchers have developed a prosthesis that restored vision to blind mice.
More than 20 million people around the world become blind because of degenerative diseases of the retina, the thin tissue at the back of the eye that turns light into a neural signal. But current prosthetics only allow a rudimentary perception of light and patients can’t recognizes faces.
With its layers of nerves, the retina seems to encode light into neural signals. In healthy eyes, the visual signal is translated into different patterns of electrical pulses as it passes from one cell to another and then on over to ganglion cells that communicate with the brain.
So, Sheila Nirenberg and Chethan Pandarinath at the Weill Medical College at Cornell University decided to crack the code that directs this series of translations. "The thing is, nobody knew the code," Nirenberg says. Without it, she believes that visual prostheses will never be able to create images that the brain can easily recognize.
They incorporated the code normally used by the retina to communicate with the brain into a high-resolution prosthetic device. This encoder translates external visual cues into patterns of electrical pulses similar to those produced by normal retinas.
They used this method to stimulate ganglion cells in blind mice. The cells fired correctly nearly 90% of the time, and the mice were able to discern facial features and visually track an image.
And here’s the methods section, according to Nature News:
- The duo injected nerve cells in the retinas of their mice with a genetically engineered virus designed to insert a gene that causes cells to produce a light-sensitive protein.
- When a beam of light was shown into the eye, the protein triggered the nerve cells to send a signal to the brain, performing a similar function to healthy rod and cone cells.
- But rather than feed visual signals directly into the eye, they processed them using the code they had developed.
- After receiving the encoded input, the mice were able to track moving stripes.
- The pair then looked at the neural signals that the mice were producing and used a different, 'untranslate', code to figure out what the brain would have been seeing.
- The encoded image was clearer and more recognizable than the non-encoded one.
Pictured: (a) original image, (b) the image after it passes through the coding software, (c) after being processed by retinal cells, and (d) processed image without coding.
They hope to test the system in humans with the next couple years. The encoding could be done on a microchip, which, together with a small video camera could fit onto a pair of glasses. The camera would record a signal and the encoder would then flash it directly onto the genetically treated nerve cells in the eye.
The study was published in Proceedings of the National Academy of Sciences this week.
[Via Nature News]
Image: Nirenberg & Pandarinath, PNAS