In a small clinical trial described in Ophthalmology, a tiny prosthetic retinal device invented by Stanford researcher Daniel Palanker, PhD, has proved its ability to restore eyesight to some people who are blind.
If you can clearly make out the big "E" on a standard eye chart at a distance of 200 feet (or if you can read the eighth line down on the chart from 20 feet away), congratulations! You've got 20/20 vision, considered normal. Someone with 20/400 vision can't read the big E on a standard eye chart from a distance of 20 feet. But if they're 10 feet away they can make it out. That's a whole lot better than nothing.
People with advanced cases of age-related macular degeneration can't see anything at all in their central field of vision, period. They do, however, retain their low-resolution peripheral vision -- they have to cast sidelong glances to get even a hazy picture of the people, places and printed materials in front of them.
The snag lies in the macula, a region in the center of the retina where light-sensing nerve cells called photoreceptors are densely packed, producing the high resolution ordinarily present in our central visual field.
Macular degeneration, which as the name implies is the progressive loss of photoreceptors in the macula, affects about 200 million people worldwide. In the United States, it's about as prevalent as all invasive cancers combined and twice as prevalent as Alzheimer's Disease. It's particularly prevalent among people of European descent.
A team of Palanker's collaborators in France recruited five patients over 60 years old with a type of advanced age-related macular degeneration that's characterized by a total loss of functioning photoreceptors in their central macula, leaving these patients without central vision. But the intermediate nerve cells to which healthy photoreceptors would have relayed signals when stimulated by light were still intact.
The researchers' goal was to restore functional central vision in one of each of these patients' eyes without jeopardizing peripheral vision in that eye. To do that, they inserted a less than 1/12-inch wide pixelated chip invented by Palanker in place of the lost photoreceptors in the patients' retinas. The surgical procedure took about two hours.
The chip is activated by augmented-reality glasses, which include a small video camera mounted on the bridge just above the nose. Images captured by this camera are beamed into the eye and onto the implant. Each pixel on that chip produces an electrical current corresponding in intensity to the amount of light it's receiving.
The electrical field generated by that current, in turn, stimulates nearby retinal nerve cells that, had there been any intact photoreceptors there, would have received those photoreceptors' inputs and sent them down the line in the brain's complicated relay system for processing visual information.
In four of the five patients, surgery was successful. (The fifth, who got only local anesthesia, moved at a critical juncture, resulting in an off-target chip insertion. The remaining four underwent general anesthesia.)
One year later, all four of those patients experienced a partial but substantial return of central vision in the eye fitted with the chip.
Using the "spectacles" to "look" at computer-generated visual-diagnostic images including bars in various orientations and letters of the alphabet, three of the patients saw an improvement from zero pre-operation visual acuity to between 20/460 and 20/550, while the fourth one, in whose retina the chip was slightly off-center, achieved 20/800 acuity. None of the patients experienced a decrease in their residual peripheral vision.
"We keep working on higher-resolution chips, with the ultimate goal of achieving visual acuity better than 20/100," Palanker told me.
Image by geralt