SAN DIEGO — A new type of prosthetic eye may someday allow blind people to seamlessly see the broad sweep of an ocean or the dimples in a baby’s face. The approach, presented November 13 at the Society for Neuroscience’s annual meeting, may benefit the estimated 25 million people worldwide who have lost sight due to retinal diseases.
“This is a spectacular example of what we all hoped to be able to do,” said Jonathan Victor, a computational systems neuroscientist who was not involved in the new work. “It’s a solution to an abstract problem” that could be useful in many kinds of systems.
Sheila Nirenberg and Chethan Pandarinath, both of Weill Medical College of Cornell University in New York City, tested their new retinal prosthetic in blind mice and found that it allowed the mice to see a baby’s face.
Current prosthetics are limited to reproducing simple features, such as bright spots or edges, but miss much of a scene. Many scientists are intent on boosting the retinal prosthetics’ power, so that the message from the artificial eye to the brain is stronger. But Nirenberg’s work suggests that a second, underappreciated area is also important: the pattern of cell activity in the retina, something she called “a big problem lurking in the background.”
Normally, cells that respond to light, called photoreceptors, pick up signals and transfer that information to ganglion cells. These cells then create a complex code for each visual signal that goes into the brain, where the scene is reconstructed. Spotting a dog creates a particular code, for example, different from the code for a teacup or a baby’s face. When a retina is degenerated, these photoreceptor cells die and there is no message to send.
Nirenberg’s new system mimics the complex behavior of the frontline photoreceptor cells, creating a more natural artificial message for the ganglion cells to interpret. Other prosthetics produce simpler, less recognizable codes, Nirenberg said. These simplified patterns aren’t what the brain is used to receiving, so while they can reproduce simple features, they can’t reproduce natural scenes. Because the new prosthetic speaks the language that the ganglion cells are accustomed to, the ganglion output — and the image — is more accurate.
“If you want to really restore normal vision, you have to know the retina’s code,” Nirenberg said. “Once you have that, the door is open to the possibility of restoring normal vision.”
To test their prosthetic system, the team decoded the output of the ganglion cells by measuring cellular activity when an image of a baby’s face was presented to the retinas of blind mice. Patterns measured from the mice with the new prosthetic reproduced a baby’s face in much finer detail than the standard method did. Instead of the standard method’s highly pixilated, blurry version of the face, the new prosthetic captured a smooth, clear view of the baby’s quizzical expression. “Not only can you tell it’s a baby’s face, you can tell it’s this baby’s face,” Nirenberg said.
The researchers are currently testing the prosthetic on primates and plan eventually to provide the technology to human patients. That would probably require gene therapy.
“Obviously it’s not in humans yet,” said Victor, also of Weill Medical College. “Everyone else is working on putting the signal into humans, and now they have the signal to put in. It’s extremely exciting.”