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Telescopic Implant Brings Sight to Diseased Eyes
August 31, 2007
Restoring vision to the blind is an age-old dream that may be within reach for patients who have the most severe form of macular degeneration, according to a study in the August Archives of Ophthalmology. But doctors have to be willing to make an unusually large incision in the eyes of their patients.
Macular degeneration eats away at the receptor-rich center of the retina, leaving a black hole, or scotoma, in the middle of the field of vision. In the most severe cases, the disease affects both eyes and is accompanied by an overgrowth of new blood vessels that leak, expanding the dark crater.
Several years ago, an Israeli researcher, Isaac Lipshitz, had the idea to create a miniature implantable telescope that would enlarge visual images so they would project onto healthy cells around the periphery of the damaged retinal center, reducing the impact of the scotoma. Ophthalmologists in the United States conducted a clinical trial of the device in 206 patients with end-stage bilateral macular degeneration. They found it improved vision and quality of life in the vast majority of patients.
Yet there was a cost. Cells lining the cornea were damaged in many patients—as many as 25 percent of cells, which exceeds the FDA’s limit of 17 percent cell death in corneal procedures. HMS assistant professor of ophthalmology Kathryn Colby, working with colleagues at several institutions, analyzed the trial results and found that much of the cell loss was due to the initial surgery, which is not surprising. “This is a very large device compared to the size of the eye,” said Colby, director of the Joint Clinical Research Center at the Massachusetts Eye and Ear Infirmary. To replace a lens in a cataract patient, doctors typically make an incision 3 mm long. To insert the miniature telescope properly, without scraping cells off the cornea, requires a 12 mm incision.
Of the 32 eye surgeons who participated in the clinical trial, the cornea specialists had the best outcomes. “We’d have made the benchmark,” said Colby, who is a cornea surgeon. “We’re used to making big wounds and then sewing them up. And we’re used to being very careful with the corneal endothelium.”
“You don’t have to be a cornea specialist to do this,” she added. “But people who are not used to making large incisions in the eye have to get used to it. That is the real take-home message—you can’t skimp on wound size.”
The device is currently awaiting FDA approval.