Nanowire retinal implant could restore sight with better resolution
Advances in bionic eyes over the past few decades have given blind and visually impaired people new hope of restoring some of their vision. Now engineers have tested a new nano-scale system that could be implanted onto a patient's retina to respond to light by directly stimulating the neurons that send visual signals to the brain. Unlike other systems, the new device wouldn't require any external sensors, and can provide a much higher resolution.
Two of the most promising bionic eyes in development are the Argus II, built by Second Sight, and a similar system created by researchers at Bionic Vision Australia. Both of these prosthetics involve first implanting electrodes into the eye, then connecting them to external sensors that can be worn like glasses. Light signals from these camera-like sensors are translated into electrical impulses and sent to the implants to stimulate the neurons at the retina, which in turn send the visual information to the brain by way of the optic nerve.
Both bionic eyes have been tested in patients with a modicum of success: far from restoring vision as a sighted person knows it, the devices produce patterns of light that a patient has to learn to interpret. But the new prosthesis, from engineers at the University of California San Diego, uses bundles of nanowires that should provide clearer vision, and do so without need of a camera.
"We want to create a new class of devices with drastically improved capabilities to help people with impaired vision," says Gabriel Silva, a senior author on the study.
The nanowires are designed to mimic the natural photoreceptor cells in the retina. When they sense incoming light, they respond by generating an electric current that stimulates the retinal cells, and these signals are sent to the brain. Since these nanowires can be arranged in a grid with a density close to natural retinal cells, the new device has the potential to provide "images" of a much higher resolution than other bionic eyes.
"To restore functional vision, it is critical that the neural interface matches the resolution and sensitivity of the human retina," says Gert Cauwenberghs, senior author of the study.
Power for the system is provided wirelessly via induction, with an electromagnetic coil outside the body relaying energy to the implant. This power is responsible for the sensitivity and timing of the retinal stimulation, and according to the researchers, is highly energy efficient, thanks to reducing energy lost in transmission. The same 13.56 MHz RF signal can also transmit data, at a rate of one bit for every two cycles.
To test their system, the researchers implanted the nanowires into a cultured rat retina, which had been engineered with a degenerating disorder. The retina was hooked up to an array of microelectrodes that would record the electrical signals that, normally, would be sent to the brain, to allow the team to study the neural activity generated by the nanowires. When the device was powered up and exposed to light, the neurons fired in response, but when either the light or electricity was taken away, they remained silent, indicating that the system works as the team hoped.
The next step for the team is to conduct tests in live animals, before eventually moving on to clinical trials. Nanovision Biosciences, a spinoff company started by the researchers, is driving that future work, with an eye towards helping patients with retinal degeneration restore some of their vision.
"We have made rapid progress with the development of the world's first nanoengineered retinal prosthesis as a result of the unique partnership we have developed with the team at UC San Diego," says Scott Thorogood, CEO of Nanovision Biosciences.
The research was published in the Journal of Neural Engineering.
Source: UC San Diego