Macular Degeneration Update
By A.Paul Chous, MA, OD, FAAO
Age-related Macular Degeneration (AMD) is the leading cause of vision loss in the Western World, and currently affects more than 9 million Americans. Although several investigations have indicated that people with diabetes are no more likely to develop AMD than people without diabetes, the underlying biology of diabetic retinopathy and macular degeneration share many similarities, and it is likely that adopting lifestyle habits to reduce the risk of one disease will lower the risk of developing the other. It is also interesting to note that a 10-year prospective study of patients with newly diagnosed type 2 diabetes showed those patients with both diabetes and AMD are more likely to experience rapid vision loss and suffer from cardiovascular disease compared to patients with AMD and no diabetes, after controlling for other known risk factors. Moreover, a recent study of Korean adults with type 2 diabetes showed a marked 87% increased risk of early AMD compared to patients without diabetes, suggesting that ethnicity may play a role. Given these findings, what should those of us with and without diabetes do to lower our risk for AMD?
Lowering the Risk
Classic risk factors for AMD include:
• older age
• history of cigarette smoking
• light eye color
• fair skin complexion
• a family history of the disease
• obesity (elevated BMI).
At least two of these are more common in people with diabetes (older age and higher BMI). One very important new risk factor appears to be a person's dietary glycemic index—essentially consumption of higher amounts of highly refined carbohydrates like bread, rice, pasta, corn, and sugar-laden beverages that quickly elevate blood sugar levels. Recent work investigating the genetics of AMD suggests that it is largely an inherited disease, though it is believed that a person's environment may determine whether certain harmful genes are activated and actually cause the disease to develop.
Lowering the risk of developing AMD can be as simple as regular fish consumption, according to the Nurses Health Study. Genetic testing for AMD risk has also become available through many eye doctors' offices, and requires nothing more than a simple cheek swab to obtain cells for sophisticated genetic analysis (medical insurance typically covers the test if you have any early signs of AMD).
Another emerging risk factor for AMD and, potentially, diabetic retinopathy is the amount of pigment in the macula at the back of the eye's light-sensitive retina, what is referred to as macular pigment optical density (MPOD). Macular pigment is comprised primarily of two dietary carotenoids (fat soluble, plant-based pigments in the foods we eat)—lutein (pronounced loo-teen) and zeaxanthin (pronounced zee-uh-zan-thin). MPOD levels are lower in patients with diabetes and in those with AMD. Increasing MPOD levels by increasing consumption of carotenoid-rich foods (kale, collard greens, spinach, orange peppers) or using supplements that contain sufficient amounts of lutein and zeaxanthin (at least 12 mg combined) improves visual function (contrast sensitivity, night vision, abnormal blind spots) in patients with early AMD and is believed to lower the risk of AMD in those at higher risk. Low MPOD levels (< 0.25) are now thought to signify increased risk for AMD, and experts believe that levels > 0.50 are desirable. Interestingly, the normal macula contains twice as much zeaxanthin as lutein, though most dietary supplements contain far more lutein than zeaxanthin. Also of note is that higher blood levels of lutein and zeaxanthin are associated with a lower risk of developing diabetic retinopathy. Many progressive eye doctors are testing MPOD levels on a routine basis and I would encourage any patient concerned about AMD to inquire about this test at their next eye examination.
So, here is my updated list of things we can all do to avoid macular degeneration and diabetes-related eye disease:
1. Keep your blood glucose levels controlled.
2. Eat a diet with less refined carbohydrate (low dietary glycemic index).
3. Lose excess body weight (every 1 point increase in BMI above 30 increases the risk of diabetic retinopathy and severe AMD by about 5%).
4. Don't smoke (it triples the risk of severe AMD)—if you do, find a way to quit.
5. Eat a healthy diet that contains lots of brightly colored vegetables and whole fruits, including dark greens (kale, collards, spinach) and twice weekly consumption of cold water, fatty fish like salmon or sardines (or a daily high quality fish oil supplement containing 650 mg EPA and 350 mg DHA).
6. Get your MPOD level tested—if it's low, change your diet and/or supplement with zeaxanthin and lutein.
7. If you have any early signs of AMD, ask your eye doctor about getting an easy, cheek swab genetic test for AMD to help minimize the risk of disease progression.
For more information on diabetic eye disease, consult Dr. Chous' book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.
NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.
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