Photodynamic Therapy

Photodynamic therapy (PDT) using Visudyne^® is a widely-used method for the treatment of wet macular degeneration. Wet macular degeneration is characterized by neovascularization (the new growth of fragile and abnormal blood vessels).

Neovascularization in macular degeneration patients is classified depending on where new blood vessels form in relation to a part of the eye called the fovea. The fovea is a small region at the center of the macula that is dense in light-sensitive cells, and provides the sharpest vision. PDT has proven to be most effective in treating wet macular degeneration when the abnormal blood vessels and their bleeding are well defined. This is particularly true in patients classified by “subfoveal” neovascularization (growth of abnormal blood vessels under the center the fovea).

There is little evidence for any beneficial effect for the use of PDT as a treatment in patients with “juxtafoveal” or “extrafoveal” neovascularization, two conditions in which the growth of new blood vessels is not directly under the center of the fovea. For these types of neovascularization, thermal photocoagulation may be a better option. This was determined following the results of the Macular Photocoagulation Study (MPS), a large scale clinical trial funded by the National Institutes of Health (NIH).

During the photodynamic therapy procedure, the light-sensitive drug, Visudyne^®, is injected into a vein in the arm. The drug enters the bloodstream and travels throughout the body. Ultimately, it is absorbed by tissues that are growing faster than normal, such as the blood vessels growing underneath the macula. A low-intensity laser light is then directed to a broad area of the retina, including the region in which the abnormal vessels are growing. The laser light activates the drug and sets into motion processes that result in the blockage of the abnormal vessels, inhibiting the neovascularization. Because the laser light is low-intensity, it does not damage the retina or other cell layers that overlie the abnormal vessels. The treatment may help to stabilize vision, but it will not restore vision that is lost and is not likely to improve vision.

Photodynamic therapy is relatively painless. It takes about 30 minutes and can be performed in a doctor’s office. Because the drug is activated by light, patients must avoid exposing their eyes or any part of their skin to sunlight or bright indoor light for up to 5 days after treatment. Headache, injection site reaction (i.e., oozing or rash), and blurred or reduced vision may occur.

In about two-thirds of treated patients, photodynamic therapy slows the rate of vision loss. It does not stop vision loss or restore vision in eyes already damaged by the disease. It is not suitable for all wet AMD patients nor for any patient with the “dry” AMD, which does not involve abnormal blood vessel growth.

Treatment results often are temporary, so photodynamic therapy is typically provided on a routine basis to prevent regrowth of the abnormal vessels.

So far, the U.S. Food and Drug Administration has approved only one drug for use in photodynamic therapy—verteporfin (brand name: Visudyne^®). Other light-sensitive drugs are in various stages of evaluation. Researchers are also studying the use of verteporfin in combination with other types of therapies.

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