MEDICAL FRONTIER

Vision of vision to millions

Los Angeles: Scientists have developed a new eye implant, using arrays of silicon nanowires that sense light and electrically stimulate the retina, which may help restore vision in millions of people worldwide. The advance brings us a step closer to restoring the ability of neurons in the retina to respond to light. The researchers from University of California San Diego and US-based startup Nanovision Biosciences showed response to light in a rat retina interfacing with a prototype of the device in vitro.

The technology could help tens of millions of people worldwide suffering from neurodegenerative diseases that affect eyesight, including macular degeneration, retinitis pigmentosa and loss of vision due to diabetes.

Performance of current retinal prostheses to help the blind regain functional vision is still limited. “We want to create a new class of devices with drastically improved capabilities to help people with impaired vision,” said Gabriel A Silva, professor at UC San Diego.

The new prosthesis relies on two groundbreaking technologies. One consists of arrays of silicon nanowires that simultaneously sense light and electrically stimulate the retina accordingly. The nanowires give the prosthesis higher resolution than anything achieved by other devices – closer to the dense spacing of photoreceptors in the human retina.

The other breakthrough is a wireless device that can transmit power and data to the nanowires over the same wireless link at record speed and energy efficiency. The new system does not require a vision sensor outside of the eye to capture a visual scene and then transform it into alternating signals to sequentially stimulate retinal neurons.

Instead, silicon nanowires mimic the light-sensing cones and rods to directly stimulate retinal cells. Nanowires are bundled into a grid of electrodes, activated by light and powered by a single wireless electrical signal

This direct and local translation of incident light into electrical stimulation makes for a much simpler and scalable architecture for the prosthesis. “To restore functional vision, it is critical that the neural interface matches the resolution and sensitivity of the human retina,” said Gert Cauwenberghs, from UC San Diego.

Power is delivered wirelessly, from outside the body to the implant, through an inductive powering telemetry system. For proof-of-concept, the researchers inserted the wirelessly powered nanowire array beneath a transgenic rat retina with rhodopsin P23H knock-in retinal degeneration.

The degenerated retina interfaced with a microelectrode array for recording electrical “spikes” from neural activity. The horizontal and bipolar neurons fired action potentials preferentially when the prosthesis was exposed to a combination of light and electrical potential and were silent when either light or electrical bias was absent, confirming the light-activated and voltage-controlled responsivity of the nanowire array.