Vitamins and the Macula
BY LEO SEMES, OD, FAAO
Two years ago, the age-related eye disease study (AREDS) reported a roughly 25 percent risk reduction for progression for patients who have moderately advanced non-neovascular age-related macular degeneration (AMD). Here's a recap of the results and recommendations of the study.
Reviewing the Facts
Patients who have category 3 (one large [>125µm] druse, extensive intermediate drusen, geographic atrophy not involving the center of the macula or any combination of these] or category 4 (fellow eye with advanced AMD but study eye with none, small or intermediate drusen, or minimal pigmentary disturbance) AMD who took the study formula progressed at a slower rate (by about 25 percent) than those in the placebo group. The study formula consisted of antioxidant vitamins and zinc, and neither treatment alone showed as great an effect as the combination.
The AREDS did face some criticism. At the time of the design and enrollment of the AREDS, lutein had little scientific standing as a dietary supplement for managing AMD.
Looking Closer at Lutein
However, over the years we have created a better definition of this protein. Lutein leads the macular supplementation pack, and here's why: Researchers have established that both lutein and zeaxanthine (macular proteins present in green, leafy vegetables) are strongly associated with reduced risk for AMD. Early investigations suggested that lutein serum concentrations were parallel to oral dosing. That is to say, they would peak appropriately and dissipate on withdrawal. The next step is to discover whether serum concentrations are reflected in macular structure or function.
A yardstick for lutein "concentration" in the macula is a psychophysical, macular pigment optical density (MPOD). Thus, the greater the lutein concentration in the macula, the more robust the MPOD. Both dietary and supplement intake contribute to total serum and macular lutein. In current research, increased macular lutein has demonstrated a treatment benefit for AMD in short-term studies on small groups of patients. But, the promise will have to be extended to longer term and larger numbers.
Beware the Blue Light
How do lutein or antioxidants act to protect against macular degeneration? We have known for some time that blue light is the biggest enemy of the macula. Lutein absorbs this harmful segment of the visible spectrum and protects the macula from the effects of oxidation. Clearly then, antioxidants may function the same way and contribute to macular stability.
While no substitute exists for a healthy diet -- and knowing that supplements can only do so much -- we can make recommendations to our patients who are at risk for AMD.
Patients showing early drusen formation -- especially large drusen -- or pigmentary changes and those whose family histories, environmental risks or occupations consist of long periods of sunlight exposure are at risk. Remember, sunlight exposure is cumulative over a lifetime. Blue-light exposure is an alterable risk factor (like cigarette cessation) for developing AMD. Encourage a healthy diet, recommend quitting smoking and offer protection from blue light.
Take Care of Your Patients
We are still scratching the surface of our knowledge regarding nutritional supplements, but recommendations will evolve. It appears from AREDS and recent work on lutein that we should recommend these formulations to at-risk patients. Patients should follow the manufacturers' guidelines regarding dosing.
Other so-called fringe supplements may be useful, but have yet to attain scientific standing. Always keep your eyes open for new information.
Dr. Semes is an associate professor at the University of Alabama at Birmingham School of Optometry.