April 23, 2008 -- Could an implantable miniature telescope give macular degeneration patients a vision boost when they run out of other options? An FDA advisory panel takes up that question later this week.
Macular degeneration, the leading cause of severe vision loss in people over age 60, slowly steals central vision, which is needed for tasks such as reading and driving. Central vision gradually goes from being a little fuzzy to near blindness.
The Implantable Miniature Telescope (IMT), made by VisionCare Ophthalmic Technologies of Saratoga, Calif., is the first of its kind. It's 4 millimeters long and designed for people with central vision loss in both eyes from end-stage age-related macular degeneration.
"End-stage" means that "there's nothing we can do that will medically improve that eye," says ophthalmologist Bill Lloyd, MD, who writes WebMD's Eye on Vision blog.
Good candidates for the telescope have severely impaired vision but aren't totally blind, Lloyd says. Patients can only get the telescope in one eye, because they need their other eye for peripheral vision, which the telescope reduces.
In the telescope's clinical trial, patients' vision improved and so did their quality of life. "It's a promising device," Lloyd says.
Kathryn Colby, MD, PhD, director of joint clinical research at the Massachusetts Eye and Ear Infirmary in Boston, agrees. "I think it's a very good device for people for whom there are no other options," says Colby, who participated in the telescope's clinical trial. "I have probably 60 patients on a waiting list that are waiting for the FDA to make its decision."
But the telescope isn't a cure -- and it does have risks. "It doesn't give people back their 20-year-old eyes which are normal in every other way. So it's very important for patients to have realistic expectations going into this," Colby says.
About Macular Degeneration
"The macula is the central-most area of your vision," Lloyd says. "Think about a map of the United States -- the macula of your retina is like Kansas City. It's a relatively small piece of real estate compared to the entire map. But nonetheless, so much of our visual input, which is 70% of what we experience in life, is processed by that tiny little island of dense photoreceptors."
In end-stage macular degeneration, "that's gone," Lloyd says. But "you still have plenty of other real estate that's not as good, not as rich in photoreceptors."
"Unfortunately," Lloyd says, the density of the photoreceptors in these outlying areas is not as precise as it was in the macula... It's not the same as seeing 20-20, but it's certainly much better."
How the Implantable Telescope Works
The telescope magnifies images by recruiting other parts of the retina to make up for the loss of the macula. "What it does is it enlarges the image that the patients can see to compensate for their macular degeneration, Colby says.
In the telescope's clinical trial, 206 patients took eye tests before getting the implantable miniature telescope. One year later, 67% of them could read at least three extra lines on the doctors' eye chart, compared to their eye test results before getting the telescope.
"One of the patients I implanted actually was able to return to a long-loved avocation of sculpting that he had had to give up," Colby says.
Implanting the telescope is "challenging surgery," says Colby, who wrote a paper about the procedure in the August 2007 edition of the Archives of Ophthalmology.
Four millimeters may sound small, but for the eye, "it's a large device, so it needs to be placed in the eye carefully to avoid damaging other structures within the eye," Colby says.
Those structures include the cornea, which is the eye's outermost layer.
In the telescope's clinical trial, patients had lost 25% of certain corneal cells one year after surgery. That didn't meet the study's benchmark of losing no more than 17% of those cells. Cornea specialists met that goal, but not all of the surgeons who took part in the study were cornea specialists, Colby notes.
The trial's results, published in Ophthalmology in November 2006, show that most of the corneal cell loss occurred from postsurgery swelling, not because of ongoing trauma caused by the telescope.
Lloyd notes that after getting the telescope, several patients in the clinical trial later needed a corneal transplant. That may be in part because of their advanced age (participants were 76 years old, on average), Lloyd says.
Tips for Patients
If the FDA approves the implantable miniature telescope, Lloyd and Colby have some advice for patients.
First, keep your expectations reasonable. For instance, "it's not realistic to hope that you're going to be able to drive," Colby says.
Second, choose your surgeon carefully. Lloyd suggests asking these questions:
- What are the risks, the benefits, and the alternatives?
- Where did you learn how to do this procedure?
- How many of these operations have you done?
- What is your success rate with this operation?
"It's early going. These things are going to require a lot of care and a lot of follow-up, and a steep learning curve," Lloyd says.