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Macular Degeneration Research

Age-related macular degeneration (AMD) is the leading cause of blindness among Americans over age 50. The macula, which is about the size of this "o," is located in the center of the retina, the area we use for reading and central vision. No one knows the exact cause of AMD, even though age is a risk factor, or how to prevent it.

Patients with early forms of the disease may not experience any symptoms. They may have drusen, or yellowish deposits underneath the retina. Patients with later forms of the disease may experience a loss of central vision and may view straight objects, such as doorways or lines of print, as wavy or curved. There are two forms of late AMD: the nonexudative, or dry form, accounting for 80-90% of affected patients, or the exudative, or wet form, which affects about 10% of patients.

Wet AMD affects one-fourth of all Americans over age 75 and can significantly damage vision. Wet AMD can cause the pigment epithelium underneath the retina to detach, distorting vision. In addition, abnormal capillaries originating from the layer behind the retina called the choroid may form and leak fluid and blood underneath the retina. The choroid's blood vessels, combined with tissue, can form a scar-like membrane under the retina and block central vision. This membrane is called a choroidal neovascularization membrane (CNVM). A majority of patients with severe vision loss from AMD have CNVM.

One of the country's leading centers for AMD research, the Emory Eye Center is conducting a number of clinical and laboratory studies aimed at preventing or halting progression of the disease.

Age-Related Eye Disease Study
The Emory Eye Center is the only center in the South involved in a National Institutes of Health-sponsored study evaluating whether antioxidants and zinc can slow or arrest progression of AMD. This five-year study, called the Age-Related Eye Disease Study, is no longer enrolling patients. The patients already participating in AREDS will be followed at least until 2000, at which time study results will be published.

Complications of Age-Related Macular Degeneration
The Eye Center is conducting the Complications of Age-Related Macular Degeneration Prevention Trial to determine whether laser treatment is effective in preventing severe vision loss from AMD.

The NIH sponsors this trial. Drusen are among the first changes to occur in AMD. Patients with drusen are particularly at risk for developing CNVM. Research has shown that standard photocoagulation laser treatment, which is used to seal leaking blood vessels with CNVM, can make drusen disappear. The goal of this study is to determine if eliminating drusen with a light laser photocoagulater can decrease the risk of later developing CNVM.

Intravitreal Injections
Emory is studying intravitreal injections of an experimental new drug to block a chemical in the eye that promotes the growth of abnormal blood vessels that occur with wet AMD. The drug is injected directly into the vitreous, the jelly that fills the eye. Participants in this Phase I study will receive one injection.

Photodynamic Therapy
Photodynamic therapy is an outpatient procedure during which researchers inject a drug, Visudyne, in the arm. The drug concentrates in the abnormal blood vessels from the choroid. A non-thermal laser light shone onto the retina activates the drug. The purpose of photodynamic therapy is to seal leakage from new blood vessel growth and slow or stop progression of vision loss from CNVM. Patients who qualify for this therapy, which was approved by the FDA in April 2000, must have a clearly defined CNVM.

Retinal Translocation Surgery
Retinal or macular translocation is an experimental new treatment involving two procedures. During the first inpatient surgical procedure, a surgeon shifts the retina aside to move the critical vision zone away from the underlying leaking blood vessels of the choroid. A few days later after the area has healed, the surgeon uses a photocoagulation laser to seal the leaking blood vessels in the choroid during an outpatient procedure. Since the laser can destroy photoreceptors on the retina and cause blind spots, it is important to move the central vision zone first.

Patients who qualify for this treatment have had a relatively recent onset of symptoms (within two to three months) with evidence of leaking or bleeding in a small area of the macula. They should have no history of laser treatment in the affected eye. The risks of this treatment are still being determined, since only a small number of patients have been treated. Several participants report that their vision has improved significantly, while a few patients have actually lost vision, a risk of undergoing the procedure.

Submacular Surgery
The Eye Center is one of 15 centers participating in the Submacular Surgery Trials (SST), which are sponsored by the NIH. An alternative to photocoagulation laser therapy, which can cause blind spots, submacular surgery involves removing the leaking area of the choroid that extends into the center of the macula. The goal of the trials is to determine whether submacular surgery can stabilize or improve vision.

Researchers will enroll patients, who will be followed for four years, into one of three trials, depending on the extent of disease and level of visual acuity. Patients who have other eye diseases affecting vision are not candidates.

Transpupillary Thermal Treatment
Like photodynamic therapy (see above), transpupillary thermal treatment involves a laser and a drug. However, thermal treatment is an alternative treatment for patients who have a poorly defined CNVM and are not eligible for photodynamic therapy. During thermal treatment, the patient receives an FDA-approved drug, which moves to the retina. Next, a retina surgeon shines an infrared laser light through the pupil onto the retina to interact with the drug and internally heat the CNVM membrane. Researchers at Emory have used the infrared laser to treat patients with choroidal melanoma for several years. The goal of thermal treatment is to seal leaking vessels associated with CNVM.

Basic Science Research
Over more than a decade, the Emory Eye Center has developed a nationally recognized team of physicians and scientists who work closely together on the study of and treatments for AMD. These physicians work hand-in-hand with a team of research scientists who have expertise in molecular genetics, immunology, drug delivery, cell biology, ocular pathology, pharmacology, and biochemistry. Emory's laboratory research includes:

Antioxidants. Emory basic scientists and physicians are studying the effects of antioxidants on retinal cells. In a study published last year, researchers found that a dietary compound found in fruits and vegetables may help prevent the development of AMD.
Retinal cell transplantation. Emory is currently developing and refining special instruments and techniques for transplanting healthy cells in the damaged retina and looking at ways to keep the body from rejecting these cells once they are transplanted. This research is in the laboratory stage, with human clinical trials possible in the next few years.
IRBP and vitamin A. Basic scientists at Emory are studying the role of IRBP, a protein that transports vitamin A within the retina. This cellular transporting process is essential for vision. Defects in IRBP may be responsible for genetic retinal diseases, including macular degeneration.
Gene therapy. Researchers in Emory's laboratories are studying gene therapy, a treatment that may replace defective genes responsible for retinal degenerations.
Drug delivery systems. Researchers are studying new ways of delivering drugs to the retina through the sclera, the white part of the eye, to treat AMD. By combining drugs with various polymers-similar to the nicotine patch-the researchers have found that this type of delivery can provide continual treatment for months.
To make an appointment with a retina specialist, call 404-778-2020.

Media Contact: Joy H. Bell

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