A team of neuroscientists and materials scientists has shown that a photovoltaic polymer can restore light-sensing capabilities to damaged retinas, offering hope of a simple way to restore vision to many people with degenerative eye disease.
Shine on: In this illustration, electrical activity (blue) moves down a neuron stimulated by a photovoltaic polymer that is exposed to light (green).
People with retinitis pigmentosa and some forms of macular degeneration lose their sight because their photoreceptor cells—the light-detecting rods and cones in their retinas—stop working or die. The new work, conducted by scientists from the Italian Institute of Technology in Genoa and published on Sunday in the journal Nature Photonics, suggests that incorporating the organic polymer into the retinas of people with such conditions could one day help solve this problem. The polymer, which converts light into electrical stimulation, does not require the power supply that’s been necessary with other artificial retina prosthetics.
Other groups have developed retinal implants—electrode arrays that replace the function of the missing cells (see “Microchip Restores Vision” and “Bionic Eye Implant Approved for U.S. Patients”). But these systems offer limited resolution and depend on stiff microchips that can’t conform to the curvature of the inner eye.
“Even a thin silicon chip is not bendable, so an organic polymer could be the next generation of potential retinal prostheses that could allow a greater coverage over parts of the retina because it allows for bending,” says Stephen Rose, chief research officer at the nonprofit Foundation Fighting Blindness.
The Italian researchers, led by neuroscientist Fabio Benfenati and materials scientist Guglielmo Lanzani, began with what Benfenati calls a “crazy idea”: to “try and grow neurons on top of these photovoltaic polymers and see whether illumination of the polymer could induce excitation of the neurons.” As he and his coauthors reported in 2011, this turned out to be possible.
In the new study, damaged retinas were placed on a piece of glass coated with the polymer. Benfenati and colleagues recorded the electrical activity of remaining retinal neurons that would normally send axons into the brain in response to light. When they shined a light onto the setup, they found neuron activity similar to what would be observed in an undamaged retina. They hypothesize that when the polymer is exposed to light, negative charges accumulate on its surface; these negative charges strip positive charges from the outside of the neuron, causing it to fire.
The retinas on the polymer-coated glass responded to daylight levels of brightness, which means the technology “has the potential for retinal implants,” says Benfenati. However, the polymer did not respond to the full range of dimness and brightness that normal photoreceptors can handle. The authors suggest that future generations of the film may be able to do so. In the meantime, they have begun testing polymer-coated implants in rats with retinitis pigmentosa.