Progress towards bionic eye implants

Silicon nanowires and wireless technology combine to produce potential high-resolution implant to restore sight

Bionic eye technology has long lagged behind the science fictional portrayal. Although some progress has been made towards restoring sight using electronics and implants, the level of sight they can produce is still well below the accepted threshold for blindness.

SEM image of silicon nanowires, which both detect light and stimulate retinal cells. Image: UC San Diego

Engineers at the University of California – San Diego and a La Jolla-based start-up company called Nanovision Biosciences now report that they have developed new technology that directly stimulates retinal cells to potentially restore high resolution sight that has been lost owing to neurodegenerative diseases, such as macular degeneration, retinitis pigmentosa and loss of sight owing to diabetes: all major causes of blindness in humans, affecting millions of people around the world and currently with no effective treatment. Although the technology is some years away from human trials, animal models have given encouraging results, the team states.

“We want to create a new class of devices with drastically improved capabilities to help people with impaired vision,” said Gabriel Silva, professor in bioengineering and ophthalmology at UC San Diego.

Two technologies are key to the system. Firstly, an array of silicon nanowires detects light and electrically stimulates retinal cells. These are bundled into a grid of electrodes whose density approaches that of the light-sensitive cells in the retina. This grid is implanted behind the retina and links up to the other key technology – a wireless device that transmits both power and data with high efficiency, using an inductive charge-transfer system that works on the same basis as wireless charging of  electronic devices or electric vehicles. The wireless signal also times the stimulation of the retinal cells. The team claims that 90% of the energy transmitted by the system is delivered to the implant and used for stimulation.

“To restore functional vision, it is critical that the neural interface matches the resolution and sensitivity of the human retina,” said Gert Cauwenberghs, a professor of bioengineering at the Jacobs School of Engineering at UC San Diego and senior author of a paper detailing the research published in the Journal of Neural Engineering. Cauwenberghs led the team that developed the inductive charging and data transfer system, which was part funded by inductive charging specialist and major semiconductor company Qualcomm.

Unlike other bionic visual systems, the team’s device does not need a camera outside the body, although one of the coils for the inductive system is outside the body – the other is implanted in the eye. This advance results from the dual action of the silicon nanowires.

The team tested the technology by implanting a nanowire electrode grid behind the retina of rats whose genome had been altered so that they developed a form of retinal degeneration. The in vitro experiment, which stimulated both rods (light sensing cells) and cones (colour sensing cells) in the retinal tissue, showed that action potentials, which indicate cell activity, were produced when the augmented retina was exposed to a combination of light and electrical potential from the inductive system. Removing either of these also stopped the action potentials being produced.

“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,” said Scott Thorogood, CEO of Nanovision Biosciences, which he formed with Silva and William Freeman, director of the Jacobs Retina Centre at UC San Diego, to commercialise the technology.

Further animal trials of the device are now progressing, with clinical trials on humans planned to follow.