Approximately one in 28 persons over the age of 40 in the United States is visually impaired. Adults over 80 years of age comprise less than 10% of the population but account for 70% of individuals with significant visual loss.
Age-related macular degeneration (AMD) is the most common cause of irreversible visual loss in older Americans.
What is Age-related Macular Degeneration?
The macula is an area of highly concentrated neurons in the central retina. Whenever a person looks directly at an object, the eyeball is instinctively moved so the image falls directly on the macula; this “sweet spot” makes it possible for the brain to receive the most detailed information possible about the object of interest.
A healthy macula is necessary for reading, driving, or recognizing detail (such as the faces of other people).
Macular degeneration occurs when the neurons in this critical area are damaged or deteriorate.
Two different forms of AMD occur:
- Exudative AMD (wet, or neovascular form): a network of fragile capillaries forms beneath the macula; these vessels bleed or leak into the area behind the retina, lifting the macula away from the underlying structures. This form – which progresses rapidly if untreated – accounts for 10% of all cases of AMD, but causes 90% of the blindness associated with AMD.
- Atrophic AMD (dry form): gradual degeneration of the macular neurons occurs without bleeding or fluid leakage into the macula.
Risk Factors for Developing Age-related Macular Degeneration
Since the specific cause(s) of AMD are unknown, all of its risk factors have not yet been fully described. Some causal associations include:
- Increasing age increases one's risk for AMD.
- AMD is more common in non-Hispanic whites than in blacks or Mexican-Americans.
- Heredity plays a role; in 2008, scientists described mutations in the SERPING1 gene – which is normally involved in clearing infections and foreign material from the eye – that were associated with higher risk for AMD (Ennis S, et al. Association between the SERPING1 gene and age-related macular degeneration: a two-stage case-control study. Lancet. 2008;372[9652]:1828-34)
- Smokers have a three times higher risk for exudative AMD than nonsmokers.
- Sunlight exposure – specifically, exposure to the blue spectral bands in sunlight – may increase risk, particularly in persons who spend more than five hours daily in the sunshine.
- Cataract excision may pose a higher risk for AMD; removal of the lens allows previously filtered light to pass unobstructed to the retina.
- High fat intake (especially trans fats) is associated with a higher prevalence of AMD in both men and women.
- Obesity – possibly due to coexisting hypertension or high dietary fat intake – is associated with a higher incidence of AMD (particularly if one’s BMI is over 30).
- Individuals with elevated cholesterol levels, cardiovascular disease, and high blood pressure are disproportionately represented among patients with AMD.
- Exudative AMD appears to be more prevalent in women than in men.
Preventing Age-related Macular Degeneration
Among the modifiable behaviors that might lessen one’s risk for AMD are the following:
- Stop smoking
- Wear hats and blue-blocking sunglasses (yellow-tinted lenses block blue light; some, such as NoIR lenses, block both blue and UV light)
- Exercise for 30 minutes at least four times weekly to help maintain ideal body weight and optimal blood pressure
- Reduce dietary fat to 20-25% of total dietary calories; decrease red meats, whole milk, cheese, and butter while increasing consumption of omega-3 fatty acids (e.g., cold-water fish, canola oil, etc.)
- Eat more green leafy vegetables and/or use lutein-zeaxanthin supplements. These pigments help to reduce the effects of blue light as it penetrates the macula
- If undergoing cataract surgery, ask about an AcrySof implant, which helps to block blue-spectrum light
- Consider taking vitamin C (500 mg), vitamin E (400 IU), beta-carotene (15 mg), zinc (80 mg as zinc oxide), and copper (2mg as cupric oxide) daily. Although this regimen has not been shown to prevent AMD, evidence shows that these supplements slow the progression of established disease. Smokers should avoid taking beta-carotene. (Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene and zinc for age-related macular degeneration and vision loss. Arch Ophthalmol 2001; 119:1417-36)
Age-related macular degeneration is a significant public health problem. There is currently no cure for atrophic AMD, and exudative AMD must be treated promptly to prevent significant visual loss. A few lifestyle changes may help to delay or even prevent the occurrence of AMD in individuals at risk.
 |
