In the latest example of neuroprosthetics, a group of researchers from across the globe, including UNSW engineers, are exploring the possibility of using photovoltaic implants to restore vision in people.
A developing area of research that has the potential to vastly improve quality of life, neuroprosthetics involves using devices designed to interact with the nervous system to restore lost functionality, much like cochlear implants, which convert sound into electric signals that directly stimulate the auditory nerve in people with severe hearing loss.
But could the same be done for the human eye to restore vision for people with damaged photoreceptors – the cells responsible for detecting light and colour? This multidisciplinary group of researchers, who include engineers, neuroscientists, clinicians and biotech experts, believes it can, though the research is still in a nascent stage.
UNSW Researcher Udo Roemer, an engineer specialising in photovoltaics, is delving into how solar technology can be used to convert light entering the eye into electricity, bypassing the damaged photoreceptors to transmit visual information to the brain.
“People with certain diseases like retinitis pigmentosa and age-related macular degeneration slowly lose their eyesight as photoreceptors at the centre of the eye degenerate,” Roemer says.
“It has long been thought that biomedical implants in the retina could stand in for the damaged photoreceptors. One way to do it is to use electrodes to create voltage pulse that may enable people to see a tiny spot.”
This isn’t the first research study into using solar cells for restoring sight, and trials with this technology reveal limitations such as the need for wires going into the eye, which is a complicated procedure.
Alternatively, a tiny solar panel can be attached to the eyeball to convert light into the electric impulse that the brain uses to create our visual fields. Being naturally self-powered and portable, the panel can operate wirelessly.
Roemer is exploring semiconductor materials such gallium arsenide and gallium indium phosphide instead of the usual silicon options, mainly because it’s easier to tune these materials’ properties.
“In order to stimulate neurons, you need a higher voltage than what you get from one solar cell,” Roemer continues.
“If you imagine photoreceptors being pixels, then we really need three solar cells to create enough voltage to send to the brain. So we’re looking at how we can stack them, one on top of the other, to achieve this.
“With silicon this would have been difficult, that’s why we swapped to gallium arsenide where it’s much easier.”
Roemer’s study is currently in the proof-of-concept stage.
“So far we’ve successfully put two solar cells on top of each other in the lab on a large area – about 1 sqcm which has got some good results.”
The next step will be to make them into the tiny pixels required for sight, and etching the grooves to separate them. It will then be a small step to increase the stack to three solar cells.
By the time this technology is ready to be tested in humans, the device will be about 2 sqmm in size with pixels measuring about 50 micrometres (five hundredths of a millimetre). However, it will be a while before this technology will be implantable in the retinas of people with degenerative eye diseases.
“One thing to note is that even with the efficiencies of stacked solar cells, sunlight alone may not be strong enough to work with these solar cells implanted in the retina,” Roemer says.
“People may have to wear some sort of goggles or smart glasses that work in tandem with the solar cells that are able to amplify the sun signal into the required intensity needed to reliably stimulate neurons in the eye.”
Source: UNSW
Retina image source: Getty Images
