Mar 4, 2009 06:05 PM | 8
When vision fails, it's often the result of damage to the eye caused by an injury or degenerative disease. In an attempt to restore such vision loss, researchers for more than a decade have been working to develop an optical prosthetic that can restore sight by delivering images directly to the brain. And it appears they succeeded. The BBC reports that a 73-year-old man identified only as Ron, who received an optical implant at Moorefields Eye Center in London last summer, can see again for the first time in 30 years.
The BBC hails the Argus II prosthetic—made by Second Sight Medical Products, Inc., in Sylmar, Calif.—as a "bionic eye," although it's actually a wireless communication system implanted in the damaged eye that captures images and relays them to the brain.
The system works with the aid of eyeglasses, which hold a camera mounted on one of the lenses that captures images and sends the information to a video processor, also located on the glasses, according to the description of the technology on Second Sight's Web site. After the video processor converts the images to an electronic signal, a transmitter on the glasses sends that information wirelessly to a receiver attached to the surface of the eye. From there, the information is sent through a tiny cable to an electrode array implanted in the retina, stimulating it to emit electrical pulses. These pulses trigger signals in the retina that travel through the optic nerve to the brain, which perceives patterns of light and dark spots that correspond to the electrodes stimulated.
In addition to Ron, 17 other patients in the U.S., Europe and Mexico are trying out the Argus II system to see if it's safe and effective in restoring at least partial vision to people suffering from Retinitis Pigmentosa (RP), a genetic eye disease that causes blindness. Preliminary results indicate that there were no device failures and few "serious adverse events," the most serious of which resulted in the removal of an implant without difficulty or harm to the individual, the company reported in November. Eleven of the study participants reported that they could locate a door up to 20 feet (six meters) away and see and walk to the end of a 20 -foot line drawn on the floor with the aid of the implant.
Other researchers are also working on prostheses designed to help the blind see again. John Pezaris, a research fellow at the Harvard Medical School, is developing one that would use electrical microstimulation in the thalamus (a dual lobed mass of grey matter cells at the top of the brainstem that receives visual sensory images) to at least partially restore vision. (Scientific American.com covered Pezaris's work in March 2008.)
The prosthesis is worn like a pair of eyeglasses, with digital cameras covering the eyes that connect to an array of electrodes implanted in the brain. This doesn't promise to restore normal vision, but Pezaris is hoping the ability to convey enough information to the brain will enable a person with complete vision loss to be able to identify simple objects and even recognize faces.
"The retinal implant technology is advancing at an impressive rate, but the most interesting thing will be to see how the volunteer subjects who have received the initial Argus II implants will fare as time goes on," Pezaris says. "The brain is highly adaptable and, while some of the initial reports in the scientific literature suggest that retinal implants may have serious problems with poor resolution, it may be that with time, the visual system of implanted patients will adapt to the
new signals, the new form of sight, with slowly improving functionality." This has been the case with cochlear implants, he adds, where the brain needs some months to adapt to the new sensory patterns.
VisionCare Ophthalmic Technologies, Inc., in Saratoga, Calif., is testing visual prosthetic devices designed for individuals with age-related macular degeneration, a disorder of the central retina, or macula, that causes the afflicted person to see a dark spot in the center of his or her field of vision, impairing the ability to read, recognize faces and watch TV. (Scientific American.com first wrote about this technology in August 2007.) VisionCare's Miniature Telescope prostheses are mini telescope-like devices that work with the eye's cornea (the transparent, dome-shaped window covering the front of the eye) like a telephoto system, rendering an enlarged retinal image that reduces the area of diminished vision.
Once implanted, the device protrudes only 0.1 to 0.5 millimeter beyond the surface of the pupil but does not touch the corneal endothelium, a layer of cells lining the back of the cornea. The Miniature Telescope has received CE Mark [[http://www.cemarking.net/ ]] approval (a mandatory European certification indicating conformity with certain health and safety requirements) and is currently being reviewed by the U.S. Food and Drug Administration, the company reports on its Web site.
Image ©iStockphoto.com/ Seb Chandler
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