Low vision — poor eyesight that can’t be corrected by glasses, contact lenses, surgery or medication — afflicts more than 2 million Americans, according to the National Eye Institute (NEI). But this is a conservative estimate. Some 14 million Americans suffer from visual impairment if you include those with eye problems that hamper the performance and enjoyment of everyday activities. While the problem has many possible causes — among them, diabetic retinopathy, retinitis pigmentosa, glaucoma and cataracts — age-related macular degeneration (AMD) is the single greatest culprit. The specific causes of AMD, marked by abnormal cell development in the macula, the central part of the retina, are not known.
Age, however, is the biggest risk factor. The prevalence of AMD increases almost fourfold between the ages of 49 and 80, according to the National Eye Institute (NEI). Women, smokers and people with a family history of AMD are at higher risk. People with high cholesterol levels may also face a greater risk for developing the so-called wet form of the disease. The wet form involves more rapid loss of sight. The dry form, which is much more common, is more gradual.
Because the condition affects central but not peripheral vision, AMD patients rarely become totally blind. But enough vision may be lost to require major changes in their lifestyle and routines.
Neither the wet nor the dry form of the disease causes any pain. The most common symptom of dry AMD is blurred vision and difficulty with reading. Some people find they need more light to read, and must be close in order to recognize faces or read street signs. As cells in the macula cease working, some people experience blurred spots in their central vision. Many people are unaware they have a problem as long as it is confined to one eye. If the second eye starts to deteriorate, the effects are more evident.
Early diagnosis may give patients more options for treatment. A doctor will look for drusen, tiny yellow deposits in the retina, and may ask the patient to look at an Amsler Grid, a patterned chart that looks like graph paper or a checkerboard. Seeing straight lines as wavy or blank spots on the grid often signals a problem. Distortions occur in AMD because the abnormal blood vessels raise the macula from its normal position.
There is no treatment for dry AMD, but since it tends to develop slowly, it doesn’t usually cause drastic vision loss until the late stages.
Vitamins and supplements
An NEI study released in 2001 found that over a six-year period, patients at high risk of developing advanced AMD who took large doses of antioxidant vitamins and minerals reduced their chances of getting the disorder by up to 25 percent. The study found that the supplements only helped those with intermediate advanced AMD, not those at the early stage.
Since the NEI research data was released, many supplement companies have stepped up their marketing of the formulation used in the study. The principal investigator on the NEI study, Emily Chew, deputy director of NEI’s division of epidemiology and clinical research, says supplements should not be taken as a preventive measure or without consultation with an eye care professional.
Still, research in this area continues. A more recent study in the February 23, 2009, Archives of Internal Medicine examines the effect of B vitamin and folate consumption in women who have heart disease, or multiple risk factors for heart disease. High levels of homocysteine are associated with both AMD and heart disease; B vitamins and folate help the body break this amino acid down in the blood. The study found that daily supplementation of B6, B12, and folic acid may reduce the risk of AMD in women.
Laser surgery to cauterize leaking blood vessels was the first procedure used to control wet AMD and is a treatment still used today. Some retinologists use lasers on small feeder vessels, trying to cut off the supply of extra blood to the larger central vessels. There are risks — if the leaky vessels are in the center of the macula, the laser may scar or destroy some retinal tissue.
In a more recent approach known as photodynamic therapy, patients are injected with a light-sensitive drug. A light is then shined on the eye and activates the drug. This treatment usually slows the rate of vision loss, but it is often temporary. Repeat treatments are often necessary, but still may not help all patients.
Other drugs, such as ranibizumab and pegaptanib, are designed to stop the growth of new blood vessels in patients with moderate wet AMD. Several studies have found both of these drugs to be effective at slowing the loss of vision and in some cases more effective than photodynamic therapy.
Clinical trials are also underway to assess the effect of implanting miniature telescopes into the eyes of AMD patients. This creates an internal magnifier for distance viewing and reading. So far, the technology is promising, with patients showing improvements in vision even two years later. Larger scale studies are needed, however.
The NEI is also funding studies into the possibility of transplanting healthy cells into diseased retina, and the potential for anti-inflammatory treatments for wet AMD. Since many of these treatments are still in their experimental stages, people with AMD should discuss them with their doctors. But don’t expect miracle cures — not just yet, anyway.
Pratt S. Dietary prevention of age-related macular degeneration. J Am Optom Assoc; 1999 Jan;70(1):39-47.
Christen WG, et al. Prospective cohort study of antioxidant vitamin supplement use and the risk of age-related maculopathy. Am J Epidemiol; 1999 Mar 1;149(5):476-84.
Age-Related Macular Degeneration: What You Should Know. U.S. Department of Health and Human Services. October 2004.
National Eye Institute. Age-Related Macular Degeneration. April 2006. August 2010.
National Eye Institute. Summary of Eye Disease Prevalence Data. December 2006. August 2010.
National Eye Institute. Low Vision and Blindness Rehabilitation. December 2006.
Colquitt, JL, et al. Ranibizumab and pegaptanib for the treatment of AMD: A systematic review and economic evaluation. Health Technology Assessment. May 2008; 12(16): iii-iv, iv-201.
Brown, DM, et al. Ranibizumab vs. verteporfin photodynamic therapy for neovascular age-related macular degeneration: Two-year results of the ANCHOR study. Opthamology. January 2009; 116(1): 57-65.
Hudson, HL, et al. Implantable telescope for end-stage AMD: Long-term visual acuity and safety outcomes. American Journal of Opthamology. 2008; 146: 664-73.
Christen, W et al. Folic Acid, Pyridoxine, and Cyanocobalamin Combination Treatment and Age-Related Macular Degeneration in Women. Archives of Internal Medicine. Volume 169, Number 4. February 23, 2009.
American Heart Association. What is Homocysteine?