CHIPPING AWAY AT BLINDNESS: There is no effective treatment for retinitis pigmentosa, but researchers such as those at Retina Implant, AG, are making great strides to remedy this through implants that stimulate still-active nerves in the retina, the layer of tissue at the back of the inner eye. Image: Courtesy of Retina Implant, AG
Promising treatments for those blinded by an often-hereditary, retina-damaging disease are expanding throughout Europe and making their way across the pond, offering a ray of hope for the hundreds of thousands of people in the U.S. left in the dark by retinitis pigmentosa. The disease—which affects about one in 4,000 people in the U.S. and about 1.5 million people worldwide—kills the retina's photoreceptors, the rod and cone cells that convert light into electrical signals, which are transmitted via the optic nerve to the brain's visual cortex for processing.
There is no effective treatment for the condition, but researchers are making great strides to remedy this through implants that stimulate still-active nerves in the retina, the layer of tissue at the back of the inner eye. In mid-November Retina Implant, AG, got approval to extend the yearlong phase II human clinical trial of its retinal implant outside its native Tübingen, Germany, to five new sites—Oxford, London and Budapest, along with two additional locations in Germany.
The company's implant is a three- by three-millimeter microelectronic chip (0.1-millimeter thick), containing about 1,500 light-sensitive photodiodes, amplifiers and electrodes surgically inserted beneath the fovea (which contains the cone cells) in the retina's macula region. The fovea enables the clarity of vision that people rely on to read, watch TV and drive. The chip helps generate at least partial vision by stimulating intact nerve cells in the retina. The nervous impulses from these cells are then led via the optic nerve to the visual cortex where they finally lead to impressions of sight.
Thus far, some patients report having a narrow field of vision partially restored, providing them with enough acuity to locate light sources such as windows and lamps as well as detect lighted objects against dark backgrounds. The chip's power source is positioned under the skin behind the ear and connected via a thin cable.
Window on the world
For those suffering with retinitis pigmentosa, Retina Implant's technology creates a small black-and-white window on the world, says Eberhart Zrenner, the company's co-founder and director and chairman of the University of Tübingen's Institute for Ophthalmic Research in Germany. Retina Implant has successfully placed chips beneath the retina of nine patients since May 2010. A 10th patient experienced a problem when their optic nerve did not forward the information on the chip to the brain.
Looking ahead, Zrenner hopes to widen patients' field of vision further. "Because our chip has independent miniature photodiodes, we could arrange three of them in a row beneath the retina," he says. The ability to produce accurate colors via retinal implants, however, is very complicated and may not be possible for years, he adds. Retina Implant has also developed an outpatient treatment for early-stage retinitis pigmentosa called Okuvision, which uses electric stimulation to help preserve retinal cells.
Sights set on the U.S.
The phase II extension expands Retina Implant's trial to an additional 25 patients beginning early next year and follows a partnership the company struck in March with the Wills Eye Institute in Philadelphia. Wills is looking to become the lead U.S. clinical trial investigator site for Retina Implant's technology and to help the company through the U.S. Food and Drug Administration's (FDA) review process.
Cutting-edge technologies such as sub-retinal implants are typically at a disadvantage when seeking FDA approval due to the lack of a track record, but Retina Implant's work in Europe provides a precedent for the FDA to consider, says Julia Haller, Wills's ophthalmologist in chief. "There's information available to U.S. regulators about how patients have responded so far," she adds.