Macular Degeneration is a loss of vision in the exact center of the field of vision. It is caused by changes to the macula, the central portion of the retina. The retina is the nerve tissue that makes up the inner wall of the back of our eye, and the macula is the central part of the retina, which is responsible for clear, sharp focus. We can see objects in our off-center (peripheral) visual field, but if we really want to see their minute details (letters, for example) we need to point our macula at the object. Macular degeneration doesn’t cause total blindness, but it worsens your quality of life by blurring or causing a blind spot in your central vision. Central vision that is lost to macular degeneration cannot be restored, but later in this article you’ll find thoughts on prevention and aids in coping with the vision loss of macular degeneration.
Macular degeneration is a general term and there are many degrees of severity, including everything from a slight blur when reading to the inability to see even the largest letters on the eye chart. There are two main forms, wet and dry, and while the risk for both forms increases markedly after the age of 60, some younger people can show early signs of the condition.
Dry macular degeneration is caused by atrophy of the small blood vessels that nourish both the photoreceptors (cones and rods) in the macula and the RPE (retinal pigment epithelium)- a thin layer behind the photoreceptors that supports them by removing waste molecules. In the early stage of dry macular degeneration, small drusen (fatty deposits) appear between the cones and the RPE. The drusen may be deposits that indicate a failure of the RPE to remove waste molecules. The vision is as yet unaffected. Later, medium sized drusen appear and the RPE is beginning to show a mottled appearance. At this point vision is slightly blurred and more light or magnification may be required for reading. Later still, there are several large drusen and defects in the RPE, which causes further damage to the photoreceptors. At this point there will be well-defined blurry or missing spots in the central vision, which may expand over time to a large blurred or missing area in the central vision. It can affect one eye initially, but generally will eventually involve both eyes.
Wet macular degeneration is a more advanced form and usually starts as the dry form. In this case, weak and abnormal blood vessels develop in the vascular layer below the macula. They grow there in an attempt to aid the damaged RPE in its job of nourishing and removing waste. However these abnormal blood vessels will eventually leak and cause sudden onset of missing areas in the central vision. A few years ago, laser treatment was the only option available to seal off these leaking blood vessels, but the side effect was always damage to the healthy tissue. Today the retinal specialist can use injectible drugs like macugen or avastin, which inhibit the growth of these abnormal blood vessels without damaging healthy tissue. Currently the injections are expensive and must be given monthly, but these drugs offer great promise for the future.
Dry macular degeneration usually develops gradually and painlessly. You may notice the need for increasingly bright light when reading or doing close work. You may notice increading difficulty adapting to low light levels, such as when entering a dimly lit restaurant. You may have difficulty recognizing faces, a decrease in the intensity or brightness of colors, or a blurred or blind spot in the center of your visual field. Your vision may faulter in one eye while the other eye remains fine for years. You may not notice any or much change because your good eye compensates for the weak one.
Examination and Detection
As part of your routine dilated eye examination, the doctor will use a special lens to view your macula. The doctor will look for the presence of drusen and mottled pigmentation in the macula. The eye examination includes a simple test of your central vision and may include testing with the Amsler grid (see below). If you have macular degeneration, when you look at the grid, some of the straight lines may seem faded, broken or distorted. By noting where the break or distortion occurs– usually on or near the center of the grid– your eye doctor can better determine the location and extent of your macular damage. Regular screening examinations can detect early signs of macular degeneration before the disease leads to vision loss.
Amsler grid testing… Hold the grid 14 inches in front of you in good light. Use your corrective glasses or reading glasses if you normally wear them. Cover one eye. Look directly at the center dot with your uncovered eye. While looking at this dot, determine whether all of the lines of the grid appear straight, uninterrupted and have the same contrast. Repeat the above steps with your eye.
Angiography — To evaluate the extent of the damage from macular degeneration and to determine if it is wet or dry, your doctor may send you to a retinal specialist for fluorescein or indocyanine green angiography. In this procedure, dye is injected into a vein in your arm and photographs are taken of the back of the eye as the dye passes through blood vessels in your retina and choroid. The photographs are then used to detect changes in macular pigmentation or to identify small macular blood vessels.
Contributing factors for development of macular degeneration include:
- Age — In the United States, macular degeneration is the leading cause of severe vision loss in people age 60 and older.
- Family history of macular degeneration — If someone in your family had macular degeneration, your odds of developing macular degeneration are higher. In recent years, researchers have identified some of the genes associated with macular degeneration. In the future, genetic screening tests may be helpful for assessing early risk of the disease.
- Race — Macular degeneration is more common in whites than it is in other groups, especially after age 75.
- Gender — Women are more likely than men to develop macular degeneration, and because they tend to live longer, women are more likely to experience the effects of severe vision loss from the disease.
- Cigarette smoking — Exposure to cigarette smoke doubles your risk of macular degeneration. Cigarette smoking is the single most preventable cause of macular degeneration.
- Obesity — Being severely overweight increases the chance that early or intermediate macular degeneration will progress to the more severe form of the disease.
- Light-colored eyes — People with light-colored eyes appear to be at greater risk than do those with darker eyes.
- Exposure to sunlight — Although the retina is more sensitive to shorter wavelengths of light, including ultraviolet (UV) light, only a small percentage of ultraviolet light actually reaches the retina. Most ultraviolet light is filtered by the transparent outer surface of your eye (cornea) and the natural crystalline lens in your eye. Some experts believe that long-term exposure to ultraviolet light may increase your risk of developing macular degeneration.
- Low levels of nutrients — This includes low blood levels of minerals, such as zinc, and of antioxidant vitamins, such as A, C and E. Antioxidants may protect your cells from oxygen damage (oxidation), which may partially be responsible for the effects of aging and for the development of certain diseases such as macular degeneration.
- Cardiovascular diseases — These include high blood pressure, stroke, heart attack and coronary artery disease with chest pain (angina).
There is no treatment available to reverse dry macular degeneration. But this doesn’t mean you’ll eventually lose all of your sight. Dry macular degeneration usually progresses slowly, and many people with the condition are able to live relatively normal, productive lives, especially if only one eye is affected. Dry macular degeneration can, however, develop into the more rapidly progressive wet type of macular degeneration at any time. In the case of wet macular degeneration, a retinal specialist can use injectible drugs like macugen or avastin, which inhibit the growth of abnormal blood vessels without damaging healthy tissue. Currently the injections are expensive and must be given monthly, but these drugs offer great promise for the future.
Taking a high-dose formulation of antioxidants and zinc may reduce progression of dry macular degeneration to advanced macular degeneration. The National Eye Institute- sponsored Age-Related Eye Disease Study (AREDS) showed that a daily supplement of 500 milligrams (mg) or vitamin C, 400 international units (IU) of vitamin E, 15 mg or beta carotene (often as vitamin A — up to 25,000 IU), 80 mg or zinc (as zinc oxide) and 2 mg of copper (as cupric oxide) reduced the risk of progressing to moderate or severe vision loss by up to 25 percent. The AREDS 2 study is currently testing lutein and zeaxanthin, which are plentiful in spinach, as well as Omega 3 fatty acids as possible protection from macular degeneration. The study won’t be completed for years, but these nutrients should be condsidered since they may also provide benefits to our cardiovascular system in general.
The following measures may help you avoid macular degeneration:
- Eat foods containing antioxidants. Foods with antioxidants are those rich in vitamins A, C and E. People who eat diets rich in vegetables, particularly leafy green vegetables, may have a lower risk of macular degeneration. The National Eye Institute is currently sponsoring a clinical trial to assess the efficacy of three specific antioxidants — lutein, zeaxanthin and omega-3 fatty acids — in lowering the risk of macular degeneration. Lutein and zeaxanthin are found in high concentrations in egg yolks, corn, and spinach and other green leafy vegetables. Omega-3 fatty acids are found in fish as well as other foods such as almonds.
- Take antioxidant and zinc supplements. For people with moderate to advanced macular degeneration, findings from the National Eye Institute-sponsored Age-Related Eye Disease Study (AREDS) indicate that taking high doses of zinc, beta carotene, and vitamins C and E is effective in reducing the risk of further vision loss. However, beta carotene has been linked to increased risk of lung cancer in smokers. Too much vitamin E can be toxic. Ask your doctor about these supplements before trying anything on your own.
- Eat fish. A diet rich in the omega-3 fatty acids found in fish can result in a reduced risk of macular degeneration.
- Stop smoking. Smokers are more likely to develop macular degeneration than are nonsmokers. Ask your doctor for help to stop smoking.
- Manage your other diseases. For example, if you have cardiovascular disease or high blood pressure, take your medication and follow your doctor’s instructions for controlling the condition.
- Get regular eye exams. Early detection of macular degeneration increases your chances of preventing serious vision loss.
- Screen your vision regularly. If you’ve received a diagnosis of early-stage macular degeneration, your doctor may suggest that you regularly monitor your vision at home with an Amsler grid. Doing so may help you to detect subtle changes in your vision at the earliest possible time and seek help promptly.
If you have some vision loss because of macular degeneration, your eye doctor can prescribe optical devices called low-vision aids that will help you see better for close-up work. Or your doctor may refer you to a low-vision specialist. In addition, a wide variety of support services and rehabilitation programs are available that may help you adjust your lifestyle.
Macular degeneration doesn’t affect your side (peripheral) vision and usually doesn’t cause total blindness. But it can rob you of your central vision — which is important for driving, reading and recognizing people’s faces. A low-vision center may be able to assess your visual capabilities and suggest certain optical and household devices that can be helpful for some near-vision tasks. Ask your eye doctor if there are any low-vision centers in your area.
There are ways to cope with impaired vision. Below are a few suggestions:
- Use caution when driving. First, check with your doctor to see if driving is still safe based on your current visual acuity. When you do drive, there are certain situations to avoid. For example, don’t drive at night, in heavy traffic or in bad weather.
- Seek help traveling. Use public transportation or ask family members to help, especially with night driving.
- Travel with others. Contact your local area agency on aging for a list of vans and shuttles, volunteer driving networks or ride shares.
- Get good glasses. Optimize the vision you have with the right glasses, and keep an extra pair in the car.
- Use magnifiers. Large-print books and magazines can help you read more easily.
- View with large type on the Internet. Look for Web sites that use large-sized type fonts, or change the font size on your display.
- Obtain specialized appliances. Some clocks, radios, telephones and other appliances have extra-large numbers.
- Have proper light in your home. This will help with reading and other activities.
- Remove home hazards. Eliminate throw rugs and other possible tripping hazards in your home.
- Ask friends and family members for help. Tell them about your vision problems so that they can help you perform certain tasks and help you recognize people.
- Don’t become socially isolated. A common frustration of people with macular degeneration is the inability to recognize other people and greet them by name. If this happens to you, try asking people you know to say hi and tell you their names when you meet them on the street or in other situations so that you can greet them back.
- Take advantage of online networks. The Internet is a good source for support groups and resources for people with macular degeneration.
Some people have turned to complementary or alternative therapies, such as bilberry, ginkgo and shark cartilage, in the belief that they can help prevent the progression of macular degeneration. However, there’s no conclusive evidence that any of these products are effective for macular degeneration, and some may interact with other medications you’re taking. Check with your doctor before taking any dietary or herbal supplement.