Mental Floss

This Visual Prosthetic Helps the Blind See Again

Jordan Rosenfeld
iStock / iStock

Millions of people around the world have forms of progressive retinal degeneration: These conditions cause blindness, slowly but surely. But a research team from the University of Pisa, Italy, just found a method to help adults retrain their brains to see again. Overturning old attitudes about the brain’s plasticity, their groundbreaking research, just published in the journal PLOS One, suggests that new visual prostheses can help these people restore visual signals to their brain.

The researchers Elisa Castaldi and Maria Concetta Morrone implanted the Argus II retinal prosthesis system in seven patients with retinitis pigmentosa, one of many retinal degenerative conditions that lead to blindness. The system sends small light pulses to the retina’s remaining cells, bypassing damaged photoreceptors, and stimulating the few remaining retinal cells. These cells then transmit this visual information along the optic nerve to the brain, allowing the person to perceive light patterns, and eventually see again. Before the surgery, all of the patients had been blind for 20 years. At the most, they had bare light perception.

“We tested the ability of our patients to detect big and high contrast shapes presented very briefly,” Elisa Castaldi, lead study author, and a post-doc in the Department of Translational Research on New Technologies in Medicine and Surgery at the University of Pisa, tells mental_floss. The subjects were asked to specify in which of two intervals—marked by two noises—there was a stationary, large, high-contrast visual stimulus. Then they had to verbally report whether it appeared in the first or second interval. “When using the prosthetic implant, they reached up to 90 percent accuracy in this task,” Castaldi says—a huge change from their normal vision.

The subjects were also hooked up to fMRI imaging that measured their brain activity by monitoring changes in their blood oxygen levels as their neurons fired, Castaldi explains. After implanting the system, the scientists found an increase of signals in a subcortical structure of the brain known as the lateral geniculate nucleus—the first relay station of visual information along the visual pathway before reaching the cortex.

Their remarkable results, however, were not immediate. The researchers found that the more time the patients spent training with the implant, the better their performance increased. In fact, most of these patients trained with their implant for months with a vision therapist at home, both to help them “localize” their physical world—interpreting the visual signals as doors, windows, and walls—as well as sitting in front of a computer and practicing recognizing “big, high-contrast shapes.”

“We observed that the recovery of vision depended on the amount of time and practice the subject experienced with the implant,” Castaldi says. Prior literature had shown that after many years of blindness, the brain reorganizes itself, and “the areas that were once used to process visual information are recruited for another purpose, like touch or hearing.” This study demonstrated that, in fact, the adult brain has greater “plastic potential” than research had previously shown, allowing people who had spent years without vision to learn to see using artificial visual input.

The results of this study, Castaldi says, are important “because it is often thought that the ability of our brain to reorganize itself and adapt to a new condition—a property called plasticity—is confined mainly to childhood.”

Now, combined with breakthroughs in visual prosthetics, research may be able to make significant strides to retrain adult brains to see again.