According to the Centers for Disease Control, age-related eye diseases represent a significant public health issue, particularly among those older than 65. This population group accounts for approximately 30% of all cases of visual impairment, one of the most feared disabilities among older adults.
The National Eye Institute (NEI) within the National Institutes of Health (NIH) estimates 38 million Americans over age 40 experience blindness or an age-related eye disease. This number is expected to grow to more than 50 million Americans by 2020.
The four most common causes of visual impairment are diabetic retinopathy, age-related macular degeneration, cataracts, and glaucoma. Management of these conditions is challenged on many fronts, including the fact that the standard of care for these conditions typically does not include a dietary component.
In 2004, health-screening data indicate that diabetic retinopathy, a common complication of diabetes, affects at least 40% of the diabetic population in the United States. This condition is the result of chronic elevated blood glucose, which directly damages the blood vessels in the eye, limits their ability to be sufficiently repaired, and ultimately results in permanent loss of vision.
Age-related macular degeneration (AMD) is an irreversible condition caused by abnormal vascularization of central retinal tissue. Approximately 54% of blindness among Americans of European heritage is attributed to AMD, the cause of which remains unknown. Various investigational/interventional treatments are in trials; all are expensive.
Cataracts, the most common form of age-related eye disease, presents as an opaque lens and subsequent diminished vision. It affects more than 50% of the American population over age 65. Some risk factors associated with cataracts include hypertension and diabetes and increased exposure to sunlight.
Glaucoma, a progressive disease that damages the optic nerve fibers, increases with age and with diabetes. This "silent thief of sight" is expected to affect 60 million Americans by 2010 and is two to three times more prevalent among older adults with African-American ancestry than among those of European heritage.
The two major types of glaucoma, primary open-angle glaucoma (POAG) and primary congenital glaucoma (PCG), may have a genetic component, CYP1B1. The CYP1B1 protein is involved in the metabolism of steroids, retinol, retinal, arachidonate, and melatonin. Based on some animal models, the diminished level or absence of this protein appears to contribute to the pathogenesis of this disease.
Reduced independence and capacity for sustaining activities of daily living caused by vision loss may, in part, represent opportunities for dietary intervention. Prophylactic intervention with some dietary components may reduce the risk of some forms of age-related eye diseases, including aspects of the visual cycle. However, some retinal dysfunctions reflect an accumulation of all-trans-retinaldehyde, which may require pharmacologic intervention in order to meaningfully reduce the level of this cytotoxic compound.
On the other hand, data from the Women’s Health Initiative suggest at least a real trend in that the consumption of foods containing the carotenoids lutein and zeaxanthin may reduce the prevalence of nuclear cataract, although the protective effect was not statistically significant. A 10-year follow-up assessment of these carotenoids and vitamins C and E among a subpopulation with 2,031 cases of cataracts suggested the consumption of lutein and zeaxanthin (6.7 mg/d) and vitamin E (262 mg/d) was associated with a decreased risk (RR=0.82 and 0.86, respectively) of cataracts between extreme quintile intakes. On the other hand, in a 7-year study (Cardiovascular Health and Age-Related Maculopathy) among 252 subjects, the consumption of dietary lutein/zeaxanthin (0.97 mg/d) and omega-3 fatty acids (2.0 g/d) was associated with approximately a 2.5-fold increase in the progression of AMD when compared to the lowest quintile.
The nutrients are not a cure for AMD, nor will they restore vision already lost from the disease. Yet nutrients are surely playing some significant role in helping people at high risk for developing advanced AMD keep their vision and independence.
References for the above studies are available from the authors.
by Roger Clemens, Dr.P.H.,
Special Projects Advisor,
ETHorn, La Mirada, Calif.
by Peter Pressman, M.D.,
Lt. Cmdr., Medical Corps, U.S. Navy