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.