FRAMINGHAM (07/24/2000) - Science fiction, move over: Artificial vision is a step closer to medical and scientific reality. Late last month, the first artificial retinas made from silicon were implanted in the eyes of three blind patients. The trio, who had lost almost all of their vision due to retinitis pigmentosa (RP), were released from the hospital the following day.
Invented by brothers Vincent and Dr. Alan Chow, who founded Optobionics Corp. in Wheaton, Ill., the Artificial Silicon Retina (ASR) is a microchip 2mm in diameter and thinner than a single strand of human hair. The silicon wafer contains some 3,500 microscopic solar cells that convert light into electrical impulses.
Designed to replace damaged photoreceptors - the eyes' light-sensing cells, which normally convert light into electrical signals - the chip runs on ambient light without batteries or wires. The ASR was designed to be surgically implanted under the retina in a spot known as the subretinal space and to produce visual signals similar to those produced by the photoreceptor layer.
In practice, the ASR works with photoreceptors that are still functional. "If the chip can interface with functioning cells for extended periods, we're well on the way to our goal of sight," said Alan Chow.
Photoreceptor loss occurs in people with RP, which is a catch-all name for many diseases that affect the photoreceptor layer. RP includes conditions such as Usher syndrome, Leber's congenital amaurosis, Stargardt's disease and gyrate atrophy.
Age-related macular degeneration (AMD) is another eye condition the ASR could help, according to the Chow brothers. AMD is associated with aging, but the exact cause is still unknown. AMD and RP affect at least 30 million people and are the most common causes of untreatable blindness.
For now, the ASR can't help people with glaucoma, which involves nerve damage; diabetic eye disease with severe retinal scarring; or blindness due to stroke or other brain injuries. "At the moment, we're trying to find out if we're in the right ballpark," says Alan Chow. "Once we do that, we can modify the parameters."
Natural vs. Artificial Vision
We see in a way comparable to the way cameras work. In a camera, light rays pass through a series of lenses that focus images onto film. In a healthy eye, light rays pass through the cornea and lens, which focuses images onto the retina, a layer of light-sensing cells lining the back of the eye.
The macula is the area of the retina that receives and processes detailed images and sends them to the brain via the optic nerve. The multilayered macula provides the highest resolution for the images we see. Damage here means reduced vision: Enter the ASR.
The thousands of microscopic cells on the ASR are each connected to an electrode that converts incoming light images into impulses. These stimulate any remaining functional retinal cells and produce visual signals similar to those generated by healthy eyes. The artificial signals can then be processed and sent through the optic nerve to the brain.
In animal tests during the 1980s, the Chows stimulated the ASR with infrared light and recorded retinal response. But, since animals can't talk, exactly what happened is unknown.
More Meaningful Results
About three years ago, the brothers had enough data to ask the Food and Drug Administration for permission to conduct human clinical trials. The first three candidates, who are 45 to 75 years old, are longtime sufferers of retinal blindness.
"We selected people with the most severe forms, so that if they achieve some degree of function, it would be more meaningful," says Alan Chow. "We're all very excited, but our biggest concern is that improper conclusions will be drawn too soon."
It will be a few weeks before specific results of the implantation can be evaluated. ASR creators stress that, at the moment, the device won't help people "see" in the way most of us take for granted.
"We'll be happy if they have light perception," said Optobionics Chief Operating Officer Larry Blankenship. "The best would be if the interface develops sufficient pixelization' [pixel density] so they can discern motion.
Ideally, they are able to discern form or shapes."
Rejection by the body isn't a problem. "Once [the ASR is] in place, a vacuum forms over it, and that's been very predictable," says Chow. Guarded enthusiasm aside, the ASR is a monumental scientific breakthrough that could banish forever the threat of some forms of blindness.
Forster is a freelance writer in Boston.