The procedure, called "macular translocation surgery with 360 degree peripheral retinectomy" (MT360), is a two-stage surgery that involves first internally rotating the retina to shift the degenerating macula to a healthy area, away from abnormally growing blood vessels and scar tissue. In the second procedure, the eye is rotated to account for the ensuing tilt in a person's visual field. The macula is the central portion of the retina and is used for activities that require fine-detail vision, such as reading or sewing.
"Until now MT360 had been used in patients with recent central vision loss from AMD in their newly affected second eye, but it hadn't been evaluated in patients who had undergone previous macular treatment," said Cynthia Toth, M.D., associate professor of ophthalmology and an eye surgeon at Duke. "We now have shown that this may be an option for patients who are experiencing continued vision loss despite previous treatments for AMD. This technique often allows us to recover a patient's reading vision. It isn't a cure, but our patients' feedback has been very exciting."
The latest Duke research into MT360 appears in the Nov. 1, 2003, issue of the American Journal of Ophthalmology. The authors are reporting that patients who have received a round of a standard treatment called ocular photodynamic therapy (PDT) and continue to experience vision loss recovered reading vision after MT360.
Macular degeneration, a disease that may cause blurring of central vision, occurs in two forms, wet and dry. The dry type is more common and occurs when deposits, called drusen, accumulate under the retina. The dry type may set the stage for the less common but more severe wet form in which blood vessels and scar tissue begin to grow abnormally beneath the retina, leading to permanent damage of the macula.
The macula is located at the center of the retina, the light-sensitive tissue lining the back of the eye. The retina converts light, or images, into nerve impulses that are carried to the brain via the optic nerve. People with AMD may gradually lose their central vision, which can seriously impact their quality of life.
The procedure requires the efforts of two surgical teams. One, led by Toth, has worked to perfect the MT360 technique, which was pioneered by Duke eye surgeon Robert Machemer, M.D., who is now retired. The second team, led by Sharon Freedman, M.D., associate professor of ophthalmology at Duke, has developed the eye muscle surgery that works in tandem with MT360. The procedure offers the possibility of restoring reading vision to patients with end-stage, or wet, AMD.
"While not everyone is a candidate, we now have more options," added Toth. "I once had to tell patients, if they had bad scarring in their eyes and we had already tried conventional therapies, that we were out of options. It's rather rewarding to be able to help someone who can now see pictures of their grandchildren or who can read again."
During the first phase of MT360, called "macular translocation surgery," a surgeon detaches the retina and rotates it, using the optic nerve as the pivot point, thus moving the macula to a healthier area, away from the abnormally growing blood vessels. Because of the rotation, however, a tilted field of vision results.
The "tilt" is corrected during a second procedure in which four of the six muscles that hold the eye in place are adjusted. The muscles are detached from the outer wall of the eye, called the sclera, allowing the eye to rotate into a position that can counteract the relocation of the macula. The muscles are then reattached. The second procedure is typically done about two months after the first, allowing the eye to heal from the initial phase of surgery.
According to the researchers, the retinal surgery would not be possible without the partnership of eye muscle surgeons who were able to develop a way to counteract the ensuing tilted field of vision.
Not all patients with AMD are considered candidates for MT360, the researchers said. The best candidates are those who have central vision loss in one eye and have experienced recent vision loss -- specifically within the previous six-months -- in their second eye. AMD affects each eye at different rates.
The researchers are quick to point out that, as with any surgical procedure, there are risks involved with MT360.
"Patients can experience retinal detachment or other complications such as bleeding that are associated with any eye surgery," Toth stressed. "Fortunately, we have lowered the risk from about a 40 percent rate of retinal detachment to less than 10 percent. Double-vision or residual tilting may also occur, which we can treat with the use of special glasses or occasionally with additional muscle surgery."
Age appears to be the main risk factor for developing AMD. According to the researchers, a person's chance of developing the disease increases with each passing decade after age 50, with 30 percent of people over age 70 exhibiting some sign of the disease. The biggest environmental and genetic risk factors include smoking and a family history of the disease.
"Macular degeneration is becoming epidemic as the life expectancy of our society continues to increase," said Michael Cooney, M.D., assistant professor of ophthalmology and director of the AMD center at Duke. "The macular translocation procedure is continuing to improve as we learn more and our instrumentation advances."
The dry form of AMD is much more common than wet, occurring in more than 85 percent of all people with intermediate and advanced forms of the disease. Two-thirds of patients with advanced AMD have the wet form, which is the most severe and leads to significantly more vision loss, according to the researchers. Approximately one in 10 patients with dry AMD will eventually convert to the wet form, which accounts for 90 percent of vision loss in patients with AMD. A patient's average chance of moving from the dry to wet form is about 2 percent per year.
While there are no treatments that can prevent vision loss in AMD patients, there are treatments that can slow its progression.
"Treatments are limited, but we're making steady progress in developing new options at Duke," Cooney said, "Our goal is to focus on delivering high-quality care to our patients based upon the latest research and to anticipate and meet as many needs of our AMD patients as possible. It isn't enough to say 'we're sorry, but there is nothing more we can do for you.'"
Research funding for the PDT study was provided by Euan and Angelica Baird, benefactors of Duke Eye Center. Some of the research facilities used during the study are supported by a grant from the National Institute of Health. Carl Park, M.D., a vitreoretinal surgeon and former associate at Duke Eye Center, is an author on the article. Park now practices in Philadelphia.
Journal
American Journal of Ophthalmology