A La Jolla based startup, Nanovision Biosciences Inc, working together with a team of engineers from the University of California San Diego, have developed the wireless electronics and nanotechnology required for a new type of retinal prosthesis.
This new development brings research a step closer to restoring the ability of neurons in the retina to respond to light. The team showed that the device responds to light in a rat retina interfaced to a prototype of the device in vitro.
Tens of millions of people worldwide suffering from neurodegenerative diseases that affect eyesight could be helped by the technology. People with loss of vision due to diabetes, macular degeneration and retinitis pigmentosa could all benefit.
Although the development of retinal prostheses has made remarkable strides in the past two decades, the performance of devices presently on the market to help the blind regain functional vision is still severely limited and perform far under the acuity threshold of 20/200 that defines legal blindness.
Gabriel A. Silva is one of the original founders of Nanovision and a professor in ophthalmology and bioengineering at UC San Diego. As one of the senior authors of the work, Silva explained that they wanted to create a new class of devices with significantly improved capabilities to help people with reduced vision.
Two groundbreaking technologies were used in the design of the new prosthesis. The first consists of arrays of silicon nanowires that sense light and simultaneously stimulate the retina electrically. The nanowires give the prosthesis a resolution that is higher than that achieved by other devices and is closer to the dense spacing of photoreceptors in the human retina. The second breakthrough is a wireless device that can transmit data and power to the nanowires at the same time. The same wireless link is used for both and it achieves record energy efficiency and speed.
One major difference between existing retinal prostheses and the researchers’ prototype is that the new system does not require a vision sensor outside of the eye to capture a visual scene. Existing systems transform signals from an external sensor into alternating signals that stimulate retinal neurons sequentially. The silicon nanowires instead mimic the retina’s light sensing cones and rods to stimulate retinal cells directly. Nanowires bundled into a grid of electrodes is activated by light directly and powered by a single wireless electrical signal. This local and direct translation of incident light into an electrical stimulation makes for a much simpler architecture for the prosthesis. This also makes the device highly scalable.
The light activated electrodes are highly sensitive due to the power provided to the nanowires from the single wireless electrical signal. The same signal also controls the timing of the stimulation.
Gert Cauwenberghs, a professor of bioengineering at the Jacobs School of Engineering at UC San Diego and the paper’s senior author noted that it is critical that the neural interface matches the resolution and sensitivity of the human retina if functional vision is to be restored. A team led by Cauwenberghs developed an inductive powering telemetry system that is used to deliver power wirelessly from outside the body to the implant.
As the device minimizes energy losses in data transmission and wireless power, and in the stimulation process, it is highly energy efficient. The power is generated by recycling electrostatic energy circulating between capacitance on the electrodes and the inductive resonant tank, and within the resonant tank. Of the energy transmitted, up to 90 percent is actually delivered and used for stimulation. This translates to less heating of the surrounding tissue from dissipated power and less RF wireless power emitting radiation in the transmission.
The telemetry system is able to transmit both data and power via a single pair of inductive coils, one on the receiving side in the eye and another emitting from outside the body. The link can send and receive one bit of data for every two cycles of the signal, which uses the 13.56-megahertz RF frequency. Other two coil systems using this frequency need at least 5 cycles for every bit transmitted.
The researchers inserted the wirelessly powered nanowire array beneath a transgenic rat retina to establish proof of concept. The rat retina suffered from rhodopsin P23H knock in retinal degeneration. The retina was interfaced in vitro via a microelectrode array that was used for recording extracellular neural action potentials in the form of electrical “spikes” from neural activity.
When the prosthesis was exposed to a combination of electrical and light potential, the bipolar and horizontal neurons fired action potentials preferentially. When either the electrical or the light bias was absent, the neurons were silent. This confirmed the voltage controlled and light activated responsivity of the nanowire array.
The full peer reviewed study was published in the Journal of Neural Engineering.