A new eye implant that transmits images to the brain is one step closer to reality. The device has already restored partial sight to patients with total vision loss. This ScienCentral News video has more.
New Vision
Millions of people struggle with the activities of daily living because of vision loss from eye diseases such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP), which damage light sensing cells in the eye's retina.
The retina, the lining of the inside of the back of the eye, consists of cells called "rods" and "cones" that detect light and translate it into electrical impulses. These impulses are interpreted by vision areas in the brain as images of the world around us.
Diseases that damage the retina are a leading cause of vision loss. "What happens is that the light sensing cells, rods and cones, are no longer there, and therefore when the light goes into the eye, the patient cannot see in these areas," explains Mark Humayun, M.D., Professor of ophthalmology and biomedical engineering at the Doheny Eye Institute, part of the University of Southern California.
Hymen Marder (left) has macular degeneration, which puts blind spots in the middle of his retinas.
Now Humayun is developing a device that mimics the function of the retina and which he hopes will one day restore a useful degree of sight in patients affected by retinal diseases. This year, in collaboration with several U.S. research centers and the Department of Energy, Humayun will begin testing an artificial retinal implant that builds on information gleaned from an earlier and simpler device first implanted by his team in 2002.
The retinal implant consists of a set of electrodes on a chip that is surgically attached to the retina. It wirelessly receives images from a tiny lightweight video camera mounted on a pair of glasses. "By electrodes we mean tiny wires that can pass the current to the retina, so the camera converts the image and then through…the tiny wires the information stimulates the remaining cells (of the retina) allowing the patient to see," he says.
The first model of the implant allowed patients to perceive light and to detect motion using just sixteen electrodes. The new model uses sixty electrodes or pixels. Humayun says the difference between the two versions of the implant, which were developed by the California-based Second Sight Medical Products, Inc., "is like a train and a plane, they're that different."
He hopes the new version will provide a level of sight that enables mobility and orientation, including the ability to detect contours of obstacles such as curbs and doorways.
Mark Humayun, Doheny Eye Institute
He says tests with the sixteen pixel model allowed his team to determine how much image information was essential to provide visual perception and what information could be eliminated or ignored to reduce the size, complexity and power demands of the implant. Those tests also demonstrated that the device would survive and function in the warm, salty environment inside the body and maintain its "biocompatibility" for a period of at least five years.
The new implant with sixty pixels, he says, is one quarter the size of the original and requires only 90 minutes to implant as compared with nearly seven hours for the earlier device.
Humayun reported at the annual meeting of the American Association for the Advancement of Science that the Food and Drug Administration has approved clinical trials of the new implant, which will take place over the next two to three years in several research centers across the U.S. Recipients of the implant must be at least 50 years old and must have previously had useful vision.
"We hope and we believe that the 60 electrode will allow much more detailed resolution," Humayun says, "but it still probably will not allow someone to read or recognize faces."
The chip is implanted in the back of the eye, and a small camera is mounted on a pair of glasses that transmits images to the chip. The signals are sent along the optic nerve to the patient's brain. image: Doheny Eye Institute/USC
That would be helpful to patients with total vision loss, he says, but not sufficient for patients with AMD whose remaining peripheral vision already allows them mobility. Exactly how much improvement can be achieved won't be clear, he says, until testing is underway. "The brain is the wildcard," he says, noting that his team was surprised by the extent to which the brain was able to "fill in" visual information from the limited number of pixels in the first model.
Humayun says he expects tests with the new implant to provide the information researchers need to design a third generation device that will have the image resolving power necessary to benefit AMD patients. That would be an implant with hundreds or even a thousand electrodes. "That's where we're headed," he says, "so we can get to the point of allowing the patients to read and recognize faces."
Based on testing of the current implant, Humayun hopes to receive FDA approval for a device that restores partial vision for RP patients to the market in two to three years. And with continued advancements, AMD patients could also see light at the end of the tunnel.
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