September 27, 2002.
By Thomas H. Maugh,
Jens was a 17-year-old nailing down railroad ties when a splinter broke off and punctured his left retina, blinding him in that eye. Three years later, while he was fixing a snowmobile, a splinter of metal broke off from the clutch, destroying his other eye.
Now 39, Jens lives in rural Canada, where he splits and sells firewood. He and his wife have eight children, and when he is not working in the forests, he programs computers, tunes pianos and gives an occasional concert. But he wanted to see again so badly that Jens - he prefers not to have his last name known - recently paid an estimated $115,000 to have surgeons in Portugal drill a hole in his skull and place an array of electrodes on the surface of his brain. The electrodes are connected to a miniature television camera and a sophisticated computer that, together, have given Jens a rudimentary form of vision.
He recently demonstrated his new sight at a New York meeting by navigating through rooms, finding doors and even driving a car briefly, avoiding obstacles placed in his path.
"This is pretty crude vision right now, if you want to compare it to what I had before," Jens said. "But fortunately, there is a good improvement compared to being blind totally."
Researchers have been struggling for more than two decades to produce some kind of artificial vision for the blind, and they are on the right track. For now, Jens is one of only a handful of people who have received newly developed treatments to restore vision, and few experts expect the number of recipients to grow rapidly any time soon. But the fact that anyone has been treated at all represents a major technological breakthrough.
Reflecting that newfound optimism, nearly a dozen labs throughout the world are racing toward a common goal - bypassing damaged components of the visual system to restore sight. Some are developing artificial retinas, some are using electrodes to stimulate neural pathways in the eye, and still others are trying to stimulate the brain directly. Few, however, have done much in humans - yet.
"We're still at a very primitive stage, in the sense of how much work will be required to produce enough vision for mobility," said Dr. William Heetderks of the National Institutes of Health. Although the prosthesis used by Jens is now being marketed to consumers, experts predict that it will be a decade before other devices see much use.
Once blindness sets in, there has traditionally been nothing more that could be done.
Now that situation is changing, as illustrated by work in two labs that seem to be ahead of the field.
At the University of Southern California's Doheny Retina Institute, Dr. Mark Humayun and Dr. Eugene de Juan Jr. have developed a miniature electrode array that can be implanted in the eye to replace a damaged retina. The array is attached by thin wires buried under the skin to a radio receiver that is implanted behind the ear.
Visual signals from a video camera are processed through a microcomputer worn on a belt, then transmitted to the receiver. The retinal array stimulates optical nerves, which then carry a signal to the brain. The signal is perceived as phosphenes, bright points of light. With correct stimulation, patterns of phosphenes can draw a picture in the mind similar to that on a stadium scoreboard, where pictures are produced by arrays of individual lightbulbs.
The preliminary results have been "encouraging," Humayun said. "The brain can make a lot of sense out of crude inputs."
Dr. Alan Chow of the University of Illinois at Chicago Medical Center has produced an implantable artificial retina, but there are substantial questions about how well it works. Chow and his brother Vincent, have developed a silicon chip 2 millimetres in diameter - smaller than the head of a pin - and half the thickness of paper. It contains about 5,000 small solar cells, each attached to a miniature electrode on the back of the chip. The idea is that light falling on the chip will activate the electrodes, stimulating the optical nerves behind the retina. However, most critics do not think the solar cells can generate sufficient electrical power to activate the nerves.
Nonetheless, Chow has implanted the devices in six patients. "All of the patients have improved visual function, sometimes quite dramatic," he said.
But he concedes that the implant may not be working the way it was designed to. Retinal cells that are physically separated from the implant "seem to have improved in function in all the patients," he said. That suggests the surgery may have triggered the release of some chemical in the eye that led to regeneration of retinal cells.
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