One of the most promising new treatments for a leading cause of blindness may also be one of the most surprising.
A chemotherapy medication commonly used to treat colon cancer is one of the medications being used to treat one type of macular degeneration, an eye disease that is the primary cause of blindness in patients over age 55.
To understand how chemotherapy can treat an eye disease, it helps to understand how macular degeneration produces vision loss.
What is macular degeneration?
Macular degeneration is a disease that affects the portion of the eye known as the macula. The macula surrounds the central part of the retina, which is the inner lining of the eye that absorbs and processes light. The macula helps focus that light for tasks that require close, concentrated vision, such as reading or threading a needle.
In the early stages of macular degeneration, vision loss may be barely perceptible. It may be more difficult to see the squares of a crossword puzzle or read directions on a box, for example.
Eventually, nearly all central vision may be lost. However, since the disease doesn’t affect peripheral vision, complete loss of vision is rare.
‘Dry’ vs. ‘Wet’
There are two forms of macular degeneration. Both begin with a build-up of small protein deposits under the cells that nourish the retina; these deposits cause no symptoms and patients may not be aware of them until they have their eyes examined.
As the condition progresses, the cells that nourish the retina begin to deteriorate. In this “dry” form of macular degeneration, vision loss progresses slowly, so central vision can remain stable for years. “Dry” macular degeneration accounts for up to 90 percent of cases.
In the remaining 10 percent, however, vision may change suddenly, with marked distortions and wavy lines. This signals the development of abnormal blood vessels that grow under the retina and cause severe scarring around the cells that nourish it. This “wet” form of macular degeneration is recognized by the appearance of blood and scar tissue under the retina. The chemotherapy drug Avastin inhibits the growth of these blood vessels and can restore vision in patients with “wet” macular degeneration.
Avastin is the standard of care for patients with colon cancer; because it inhibits blood vessel growth in colon cancer tumors, ophthalmologists began using Avastin “off-label” (outside the scope of its approved usage) to treat macular degeneration patients. About a year later, the company that made Avastin released Lucentis, a non-chemotherapy form of Avastin that was then FDA-approved for macular degeneration treatment. Patients who have been treated with injections of Lucentis or Avastin have seen dramatic results; some legally blind patients have regained enough vision to read again. Treatment may need to be repeated in order to maintain the positive effects.
While there is currently no treatment for the “dry” form of macular degeneration, recent clinical research has suggested that certain nutrients may help reduce its progression.
The Age-Related Eye Disease Study (AREDS), a large, 10-year clinical trial sponsored by the National Eye Institute, suggested that multi-vitamins, antioxidants, copper and zinc could reduce progression by up to 30 percent over a five-year period. In another study, patients who ate three servings of spinach per week had a 43 percent lower risk of developing macular degeneration. Diets high in antioxidant carotenoids, colored pigments normally present in the macula that serve as a kind of protective coating against light damage, are associated with a decreased risk of the disease. Lutein and zeaxanthin are two such carotenoids.
Flavonoids, another group of natural antioxidants present in a wide range of fruits and vegetables, also are being studied as potential beneficial nutrients for the prevention of macular degeneration. Flavonoids evolved to protect plants from the oxidative damage induced by chronic exposure to ultraviolet light. They are believed to have many health benefits, including protection from cardiovascular disease and cancer.
In a collaborative effort between The Scripps Research Institute and The Salk Institute, we have been testing a variety of nutritional flavonoids to identify which specific compounds protect cells from the type of injury that leads to macular degeneration. Based on our early findings, we have compiled a list of fruits and vegetables with the highest concentrations of flavonoids found to be most effective. These vegetables include spinach, wild greens, onions (especially yellow), tomatoes, celery, hot peppers and chives. Among fruits, cranberries, cherries, blueberries, strawberries, kiwi, grapes, apples and citrus juices may be good choices.
” Anne M. Hanneken, M.D. is an ophthalmologist with Scripps Memorial Hospital La Jolla. Join Dr. Hanneken for a free seminar on macular degeneration on Friday, March 14, at 10 a.m. at the Schaetzel Center on the hospital campus. To register, call (800) SCRIPPS (800-727-4777).
