Laser-Powered Eye Implants May Help Restore Vision
New eye implants powered by lasers could one day help restore sight, researchers say.
Scientists worldwide are developing a variety of prostheses that stimulate the retina, the light-sensitive part of the eye, to restore some level of vision. But these devices often involve cameras mounted in glasses that feed visual data to electronics implanted in the eye.
Current retinal prostheses are typically powered by inductive coils, much like certain rechargeable toothbrushes are, and therefore require complex surgery to implant the power receivers. As an alternative, some inventors have tried developing retinal prostheses that are solar-powered instead. The main challenge these devices have faced is how "they would need light at least 1,000 times brighter than that seen on a sunny day to work,"biomedical engineer and physicist James Loudin at Stanford University told InnovationNewsDaily. [Virtual Reality Contact Lenses Could Be Available by 2014]
One might imagine devising goggles that fed these implants the levels of light they would need to work, since the people wearing them would need camera-equipped glasses anyhow. However, such bright levels of light would easily damage any functional vision cells that might remain — for instance, some functioning vision cells typically linger in the eye with age-related macular degeneration, one of the most common causes of blindness. These super-bright goggles could also blind anyone else who inadvertently picked up and wore the eyewear.
Now Loudin and his colleagues have developed an ingenious strategy that could make light-powered eye implants a reality. Instead of using visible light, they rely on near-infrared laser pulses that have no effect on retinal cells.
Their strategy begins with goggles mounted with a camera. A portable computer processes video data from the camera and feeds it to video projectors located within the eyewear, which shine near-infrared pulses of light at implants placed within the retinas. Photovoltaic electronics similar to ones found in solar power cells convert this light to electricity that powers the implants. The near-infrared pulses also carry video data the implants convert to electrical signals that stimulate the retina, which in turn sends visual information to the brain.
"It was actually very tricky building a near-to-eye projection system 1,000 times brighter than ambient light," Loudin recalled. "No one's ever built something like that before."
Experiments performed with rat retinas showed the system could work. The small amount of light energy used — 0.2 to 10 milliwatts per square millimeter — also falls 100 or so times below safety limits for the human eye.
The eyewear should not need complex equipment to center its light pulses on retinas. "If you've ever worn commercial video goggles, when you put those on, you automatically know where to look — your eyes turn until they see the 'screen,'" Loudin said. "The exact same thing should apply here — the patients will look around until they see the near-infrared pulses."
The implants stimulate patches of retina each measuring only about 70 microns wide, or less than the width of a human hair. "That's pretty good for our field," Loudin said. "We do want to see how much farther we can take it, how much higher we can improve the resolution of images."
The scientists detailed their findings online May 13 in the journal Nature Photonics.