Eye Diseases: Age-Related Macular Degeneration (AMD)
In macular degeneration, damage to the macula (the central spot on the retina) causes diminished central vision.
Macular degeneration (MAK-yu-lar DEE-gen-or-a-shon) is a chronic, progressive disease that gradually destroys sharp central vision. It affects up to 10 million Americans and is so commonly associated with aging that it is also known as “age-related macular degeneration,” or AMD.
The leading cause of vision loss in those older than age 50, AMD occurs due to a deterioration of the macula, a tiny spot in the central portion of your retina comprised of millions of light-sensing cells that help produce central or “straight-ahead” vision.
As you age, these light-sensitive photoreceptors in the macula – the Latin word for “spot” – become thin, worn or damaged and covered with tiny hyaline deposits known as drusen. This can cause objects directly in front of you to appear blurry and lack in detail; AMD doesn’t affect peripheral (side) vision. There may be a fuzzy “hole” in vision. For instance, when looking at a face, an AMD patient may only see the ears clearly or when viewing a frame picture, the frame may be in focus but not the artwork itself.
There are two types of AMD:
- Dry macular degeneration occurs because of a thinning in the tissues in the macula and a dysfunction in the light-sensitive cells. This initially produces subtle vision loss, such as a fuzzy appearance of objects and eventually blank spots over the eye’s central vision. Dry AMD causes about 90 percent of cases.
- Wet macular degeneration is characterized by the development of abnormal blood vessels in the area between your retina and a layer of supporting tissues behind it, called choroid tissue. As these blood vessels leak fluid, they damage retinal cells. Over the course of days or weeks, scar tissue forms, creating a blind spot in the center of your vision. Although wet AMD occurs in only about 10 percent of cases, it’s responsible for nearly 90 percent of severe vision loss from this disease.
What causes these changes is unclear, but age and heredity appear to be the main culprits, although gender and race appear to play a role. Women are more likely than men to get AMD and it affects about one in nine Caucasians between ages 65 to 74 and approximately one in four older than age 75 but is uncommon in Asians, African-Americans, Americans Indians and other groups. Researchers also suspect these other risk factors:
- Long-term exposure to light, especially ultraviolet light and blue light (the wavelength just above ultraviolet)
- Low blood levels of minerals and antioxidant vitamins, such as A, C and E
- Cigarette smoking
- Heart disease, high cholesterol and other circulatory problems
- A diet rich in partially hydrogenated fats, such as those found in margarine and many snack foods
AMD usually develops gradually and painlessly. Symptoms of the disease tend to vary, depending on the type of macular degeneration you develop.
In dry AMD, you may notice:
- A gradual haziness in vision
- A “grayness” in vision and colors appearing to be more dim
- A blind spot in the center of your visual field
- Printed words becoming increasingly blurry
- In advanced cases, faces and printed words may become hard to recognize
In wet AMD, you may notice:
- Visual distortions, such as straight lines appearing wavy
- Sudden, decreased central vision
Although you cannot change your genetic makeup or stop Father Time, there are steps you can take that may increase your chances of preventing AMD or keep it from advancing:
- Eat healthfully. A diet rich in fruits, vegetables and other foods containing antioxidant vitamins A, C and E is believed to help prevent AMD. Good sources of these nutrients include deep green, yellow and orange produce such as cabbage, broccoli, chard, spinach, squash, cantaloupe, mango and sweet potatoes. Some researchers also suspect that food containing lutein and zeaxanthin — found in high concentrations in egg yolks, corn and spinach — may be beneficial. Many experts recommend at least five pieces or servings of produce each day. And some research suggests that zinc-rich foods such as oysters, fish and legumes may also offer a protective effect.
- Consider vitamin supplements. In addition to eating well to help prevent AMD, those diagnosed with the disease may lower their risk of advanced AMD by taking vitamin supplements. In a study published in the October 2001 issue of Archives of Ophthalmology, researchers found that that people at high risk of developing advanced stages of AMD lowered their risk by about 25 percent when they consumed a daily supplement rich in vitamins C and E, beta-carotene and zinc.The specific dosages used in the study included 500 milligrams of vitamin C, 400 international units of vitamin E, 15 milligrams of beta-carotene, 80 milligrams of zinc as zinc oxide and 2 milligrams of copper as cupric oxide. (Copper was added to prevent copper deficiency, which may be associated with high levels of zinc supplementation.) These dosages exceed the RDA and what is in most multi-vitamin formulas sold over-the-counter, so consult with your doctor before starting this or any vitamin therapy.
- Wear sunglasses when outdoors to help block out harmful ultraviolet rays. Orange, yellow, or amber-tinted lenses can filter out both ultraviolet and blue light that may damage your retina.
- Quit smoking. Smokers are two to three times more likely to develop AMD compared to non-smokers.
- Drink wine. A 1998 study found that people who drank wine in moderation were less likely to develop AMD. Although this finding needs additional study, and many experts don’t advise you start drinking wine if you don’t already, other research has found that drinking one glass of wine each day offers a protective effect against heart disease, which is also a risk factor for AMD.
- Get regular eye exams. Early detection of macular degeneration is the key to preventing serious vision loss. If you’re older than age 50, eye exams generally are recommended every year – especially if you have a family history of AMD. Eye exams are also important because a simple vision test using an Amsler grid — a chart with a grid of straight lines that may appear wavy, blurred or dark if you have a vision problem — can detect early changes in your vision that may otherwise be difficult to detect.If your doctor suspects wet macular degeneration, you may undergo a procedure known as fluorescein angiography to detect leaky blood vessels under your retina. In this procedure, fluorescent dye is injected into a vein in your arm and photographs are taken as the dye passes through blood vessels in the back of your retina and choroid to detect abnormalities in these blood vessels and the surrounding tissue.
Photodynamic therapy is sometimes used to treat some forms of macular degeneration. This procedure combines a cold laser and intravenously injecting a light-sensitizing dye that concentrates in the newly growing blood vessels under the macula. When the dye is hit by light from the laser, it releases substances that close off the blood vessels without damaging the retina.
Some people with wet AMD can be treated with:
- Macular translocation surgery, a new treatment in which a fold in the wall of the eyeball is created to move the central part of the macula from leaking blood vessels. To qualify for this procedure, you must have recent vision loss and healthy tissue in that portion of the macula.
- Thermal laser surgery, which is sometimes used in early stages to seal off blood vessels that have developed under your macula. However, the results are often disappointing and only 20 percent of AMD patients are candidates for this procedure.
In most cases, it’s not possible to reverse damage caused by AMD. But there are ways to cope with the disease and make the most of the sight you have. Using magnifiers and large-print books can help you read, and you can purchase large-face clocks and telephones; bright light may also help. AMD patients are advised to avoid driving at night or in heavy traffic and to remove hazards in their home, such as throw rugs and other tripping hazards.