The researchers used mice that were genetically engineered to express one of these proteins, channelrhodopsin, in their ganglion cells. Then, they presented the mice with an image that had been translated into a grid of 6,000 pulsing lights. Each light communicated with a single ganglion cell, and each pulse of light caused its corresponding cell to fire, thus transmitting the encoded image along to the brain. “Right now, you can’t get individual cells to fire using electrodes. With channelrhodopsin, you can target individual ganglion cells,” Nirenberg says.
In humans, such a setup would require a pair of high-tech spectacles, embedded in which would be a tiny camera, an encoder chip to translate images from the camera into the retinal code, and a miniature array of thousands of lights. When each light pulsed, it would trigger a channelrhodopsin-laden ganglion cell. Surgery would no longer be required to implant an electron array deep into the eye, although some form of gene therapy would be required in order for patients to express channelrhodopsin in their retinas. Nirenberg and Pandarinath have begun collaborating with a specialist in retinal gene therapy, University of Florida ophthalmologist William Hauswirth.
“It’s a pretty novel strategy. I haven’t seen anything out there like that yet,” says Ed Boyden, a bioengineer at MIT and one of the originators of optogenetics. “The data looks as if they could do certain things that could be quite powerful, stimulating the retina in a way that can cause neurons to more accurately simulate normal vision.”
In the meantime, the deciphered retinal code can also be applied to implants already on the market. Nirenberg is in talks with retinal-prosthesis maker Second Sight, in Sylmar, California, which has implanted electrode array devices in a number of patients. “We would just take their software out and put our software in,” Nirenberg says. “It’s going to take some time to do the gene therapy version, so let’s at least do something with the patients who already have the electrodes implanted.”