Flexible solar cell implant could restore vision

The first flexible retinal implant could restore some vision to people with certain forms of visual impairment.

Conditions such as age-related macular degeneration occur when some of the photoreceptors in the eye stop functioning properly. But as other parts of the eye still work, it should be possible to restore vision using an implant that mimics the photoreceptor layer, says Rostam Dinyari at Stanford University in California.

To achieve this, an implant needs to convert a light signal into an electrical pulse – in other words, perform like a solar cell.

But most solar cells are rigid, which makes them far from ideal for use inside the eye. "If you have a lens, the focal plane is always curved and the best picture forms on a spherical surface," Dinyari says. This is why the retina is curved.

Rigid implants

Using rigid chips, a large number of small implants must be fitted in order to approximate the curve of the retina. A flexible implant would simplify matters.

"You would need a lot of surgery to implant a large enough number [of rigid implants] to cover the retina," says Dinyari. A flexible implant "would use just one surgical procedure".

While several companies are developing rigid implants, Dinyari and colleagues have designed a flexible silicon implant. They did so by carving deep grooves into the silicon between adjacent solar cell pixels that are each just 115 micrometres across.

The implant would be inserted over the most damaged part of the retina. A glasses-mounted camera would capture video, convert it to near-infrared signals and project it directly onto the implant.

Projecting images

When hit by the light, the solar cells inject current patterns corresponding to the projected images into neural tissue, which ultimately arrive at the visual cortex via the optic nerve. Near-infrared signals are used as they do not interfere with the surrounding intact photoreceptor cells, which send signals to the brain as normal.

Initial trials using retinas extracted from pigs showed that the implant could be inserted without damaging the fragile solar cell array. The team hope to implant the device into a live pig soon, before testing it in humans.

Jason Dowling at the Australian eHealth Research Centre in Herston, Queensland, thinks the approach is interesting. "To the best of my knowledge I think this is the first implant which is shaped to the curved surface and this [approach] makes a lot of sense," he says.

Dinyari presented his work at the 2009 IEDM conference in Baltimore, Maryland, last week.