STIMULATING SIGHT: Retina Implant's subretinal device is a three- by three-millimeter micro-electronic chip (0.1 millimeter thick), containing about 1,500 light-sensitive photodiodes, amplifiers and electrodes. The chip is implanted directly under the retina to generate artificial vision by stimulating inner retina nerve cells. Image: COURTESY OF RETINA IMPLANT AG
Scientists have been working for decades to create an optical prosthesis that restores at least partial vision to those suffering from retinitis pigmentosa, macular degeneration and other retina-damaging diseases. Some retinal implants have begun to deliver on that promise, but the challenge remains for researchers to develop a technology that, in addition to providing clear images, can be worn comfortably over the long term.
Germany's Retina Implant, AG, thinks it has made great strides in both areas, an assertion that will be put to the test later this year when the company launches its second clinical trial, placing subretinal (under retina) implants in about 50 patients over the next few years. Meanwhile, Sylmar, Calif.–based Second Sight Medical Products plans to make its epiretinal (over retina) implants commercially available in Europe later this year. Researchers at the Massachusetts Institute of Technology and other institutions and medical technology companies are likewise developing retinal implants—the retina lines the eye's inner surface and records images in patterns of light and color—but are not as far along as Retina Implant or Second Sight.
Retina Implant's initial human clinical trial, started in 2005, improved the eyesight of 11 patients to the point where they were able to recognize objects as well as see shapes so clearly they could combine individual letters to form words or, essentially, read at a basic level at normal reading distance and in regular light conditions, says Eberhart Zrenner, the company's co-founder and director and chairman of the University of Tübingen's Institute for Ophthalmic Research in Germany. Zrenner presented the trial's results in May at the 2010 Association for Research in Vision and Ophthalmology's annual meeting in Fort Lauderdale, Fla.
Retina Implant's second clinical trial seeks to implant the latest version of the company's technology in a larger pool of patients. The new implant no longer has external parts—its power supply is positioned under the skin behind the ear, connected with a thin cable that leads to the eyeball so that the chip does not move once implanted. (This could damage the chip.)
Retinitis pigmentosa kills the retina's photoreceptors, which are the rod and cone cells that convert light into electrical signals for the brain, leading to vision loss. This disease, one of the most common forms of inherited retinal degeneration, affects about one in 4,000 people in the U.S. Age-related macular degeneration (AMD), a leading cause of vision loss in the U.S. among people 60 years and older, gradually destroys sharp, central vision. The macula (the light-sensitive retinal tissue at the back of the eye) degenerates in two ways: In "dry" AMD the macula's light-sensitive cells slowly break down; in the "wet" form abnormal blood vessels behind the retina start to grow under the macula, thereby displacing it.
Retina Implant's device is a three- by three-millimeter microelectronic chip (0.1 millimeter thick), containing about 1,500 light-sensitive photodiodes, amplifiers and electrodes that is implanted directly under the retina to generate artificial vision by stimulating inner retina nerve cells. The chip, which is placed in the retina's macular region, absorbs light entering the eye and converts it into electricity that stimulates any still-functioning retinal nerves. This stimulation is relayed to the brain through the optical nerve.
It takes the brain one or two days to adapt to chip-assisted vision, according to Zrenner. "Lines are typically all that can be expected to be seen initially by people with retinal implants," he says. "However, scientists are finding that the human brain can quickly retrain itself to interpret the lines and shapes of different gray levels into meaningful images." With the aid of a chip one Retina Implant patient reported seeing images and words slightly flickering as though they were viewed through small waves at the bottom of a pool, Zrenner adds.