Thursday, April 02, 2009
Implantable Telescope for the Eye
A new device may help restore sight for people with severe macular degeneration.
By Emily Singer
Fighting blindness: A miniature telescope (show above) implanted into the eye improves vision in people with macular degeneration. The four-millimeter-long implant contains two wide-angle glass lenses, which magnify images onto the retina.
A miniature telescope implanted into the eye could soon help people with vision loss from end-stage macular degeneration. Last week, an advisory panel for the Food and Drug Administration unanimously recommended that the agency approve the implant. Clinical trials of the device, which is about the size of a pencil eraser, suggest it can improve vision by about three and a half lines on an eye chart.
"This is one of the few options for people with end-stage macular degeneration," says Kathryn Colby, an eye surgeon at the Massachusetts Eye and Ear Infirmary, in Boston, who helped develop the surgical procedure used to implant the device.
Macular degeneration is the leading cause of blindness in people age 65 and older, affecting more than 10 million Americans. The disease strikes the center of the retina, called the macula, which is especially important for reading, watching television, and recognizing faces. While some treatments exist to slow progression of the disease, no treatments are currently available for those in the latest stages of the disease, who have irreversible damage to the macula. An estimated 50,000 to 70,000 people per year fall into this category.
The implant, developed by VisionCare Ophthalmic Technologies, a start-up based in Saratoga, CA, consists of two lenses within a small glass tube. Once inside the eye, it works like a fixed telephoto lens, acting in conjunction with the cornea to project a magnified image of whatever the wearer is looking at over a large part of the retina. Because only the central parts of the retina are damaged in the disease, magnifying the image on the eye allows the retinal cells outside the macula to detect the object and send that information to the brain. (These cells are normally involved in peripheral vision and normally generate low-resolution visual information compared to the macula cells--you can't read a sign in your periphery, for example. But magnifying the image also has the advantage of making it easier for the cells to interpret.)"This change in vision is significant to patients," says Allen Hill, PCEO of VisionCare. In addition to improving vision, it "provides the ability to have normal eye contact, which is a crucial part of social interaction," says Eli Peli, a scientist at The Schepens Eye Research Institute, who has consulted for the company.
During the implant procedure, surgeons first remove cataracts from the eye. (Because both macular degeneration and cataracts are age related, most patients with end-stage macular degeneration also have cataracts.) They then insert the telescope, which is held in place by the resident tissue.
The device is implanted in only one eye--patients use this eye for detailed vision and the untreated eye for peripheral vision. That takes some getting used to, says Peli. "Instead of using two parts of the same eye, they must switch between two eyes; if they see someone coming but can't tell who it is, they need to switch to other eye."
One safety concern associated with the implant is loss of the endothelial cells that are responsible for keeping the cornea transparent. While cell loss occurs with any eye surgery, implantation of the telescope requires a larger incision than typical cataract surgery and thus destroys more endothelial cells. However, scientists have found that cell loss stabilizes over time. Patients with the implant lose about 3 percent of their endothelial cells per year, compared to about 2.5 percent to 3 percent for patients undergoing traditional cataract surgery. Because endothelial cells replicate, substantial loss of these cells can worsen vision.
The FDA is expected to approve the telescope, as the agency usually follows the advice of its advisory panels. VisionCare plans to market the device following FDA approval, estimated for late 2009. The device has already been approved for use in Europe, though the company plans to launch the product first in the United States.