Understanding the risk factors for macular degeneration
Q: I was recently diagnosed with wet macular degeneration and am now receiving periodic injections for the disease. What causes it? Are there any risk factors, such as drugs or diet?
A: Age-related macular degeneration (AMD) is the leading cause of adult blindness in industrialized countries. AMD causes damage to the central portion of the retina, leading to a loss of central (foveal) vision. Central vision is necessary to see those details that allow people to read, drive, watch TV and perform many of the activities of daily living.
There are two types of AMD, a dry type and a wet type. Each causes a change in the retina, which consists of layers of cells in the back of your eye. For those who remember using a camera with film, the retina is like the film upon which images are exposed.
Dry AMD is much more common than wet AMD, constituting 85 to 90 percent of all cases. There has been no single cause established for dry AMD, which occurs when a mixture of protein and fat (called drusen) builds up behind the retinal layers. Dry AMD leads to a slow progression of vision loss that occurs over many years. People with dry AMD in both eyes have a 1 to 4.7 percent yearly risk of developing wet AMD.
As for wet AMD, it's caused by the growth of abnormal blood vessels behind the retina. These blood vessels leak, causing both fluid and blood to pool behind the retina. I regret to say that without treatment, the prognosis is not good. The condition can lead to rapid vision loss, causing blindness within months or even weeks. While wet AMD accounts for only 10 to 15 percent of all cases, it accounts for 80 percent of the blindness caused by AMD.
The biggest risk factor for both types of AMD is age, with people ages 55 to 64 having a 0.2 percent risk of developing the condition, and those older than 84 having a 13.1 percent risk. Smoking cigarettes increases the risk of developing AMD by a factor of two to four, and the risk persists many years after stopping smoking. It also causes the degeneration to progress faster.
Other risk factors: Having a family history of early-onset or severe AMD and having had a prior stroke or heart attack. There may be an association between AMD and aspirin or blood pressure medications (especially beta-blockers and nitroglycerin), but as of now no causality has been defined. Heavy alcohol consumption (more than three drinks per day) has been associated with early-onset AMD, but not with late-onset.
In regards to diet, one study followed the dietary habits of 2,525 patients with age-related eye disease. Those who adhered to a Mediterranean diet had a 26 percent reduced risk of developing advanced, severe macular degeneration. Mediterranean diets are high in nuts, fish, vegetables, fruits and whole grains and low in red meat, processed meats and saturated fats.
Antioxidant combinations that include vitamin C and vitamin E, as well as supplements of lutein with zinc, have also been linked to a decreased risk in progression of AMD. So it is possible that deficiencies in these substances may increase your risk.
People who want to decrease their risk factors for AMD should stop, or not start, smoking; they should avoid heavy alcohol use; and if their diet is high in saturated fat, they should consider switching to a Mediterranean diet.
• Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.Send your questions to askthedoctors@mednet.ucla.edu