A number of research teams around the world are working on various versions of the artificial retina in the hope that one day the blind will be able to see.
For blind people, recovering even the slightest bit of vision would be a revolutionary step. Just being able to see the outline of a doorway would propel blind people into a different world.
We're getting closer to this goal. A number of research teams around the world are working on various versions of the artificial retina, formally known as the intraocular retinal prosthesis. While the devices are still undergoing rigorous testing and development, results to date have raised hopes as well as cautions.
In research conducted in Southern California with the Argus device, blind people who have had the device implanted report that they can see some light and detect objects and motion. This is vision in its most rudimentary form. The six blind people tested were able to distinguish large, simple shapes (such as the capital letter L) 60-80% of the time. They did better with objects and were able to indicate whether a cup, a plate, or a knife had been placed before them. A second-generation device, the Argus II Retnial Stimulation System is now in Phase II clinical trials.
The Argus has several components. A thin chip with 60 electrodes on it is implanted in the eye, and a second chip is implanted behind the ear. The final component is a pair of sunglasses equipped with a miniature video camera and a microprocessor. When the blind person wears the glasses, the video camera captures images and converts them to electrical impulses that are transmitted to the chip behind the ear, which then relays them to the retinal chip.
The retinal chip functions in lieu of damaged rods and cones and sends impulses directly to the retinal ganglion cells, which pass them along to the visual cortex of the brain. In the original Argus, for each electrode stimulated on the chip, the blind person saw one or more dots of light, perhaps a string of lights, not a formed image. The Argus II has much higher resolution than the original device. However, it is still considered rudimentary.
The Argus has been implanted in patients with retinitis pigmentosa (RP, a rare, inherited disease that leads to tunnel vision and then blindness) and researchers hope to eventually test it in people who are blind from age-related macular degeneration. While RP and AMD damage the structures of the eye that normally convert light to electrical impulses, they spare the neural paths to the brain that transport the electrical signals. Blind people with diseases that damage the optic nerve wouldn’t be eligible for the artificial retina.
What's Next? This research has raised many questions, including the following:
- How much current can the retina tolerate?
- What’s the best site for the chip to be implanted in terms of yielding the best perception and requiring the lowest, safest electrical charge needed to stimulate neurons?
- Will the retinal neurons tolerate long-term electrical stimulation without being altered in any way?
- Another question researchers have been grappling with is how many light-producing electrodes can fit on a chip without damaging the retina? That is, how do you provide enough power, but not so much that it generates tissue--destroying heat?
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Posted in Vision on April 27, 2007
Reviewed July 2009
