Age-related macular degeneration is a leading cause of poor vision in people over age 60. It is rarely found in younger people.
Central vision is the vision in the center, or straight ahead. For most people, central vision provides the sharpest and most useful vision. When the macula of the eye deteriorates or is damaged, central vision is affected. Things may become distorted, blotted out, or obscured in a haze. Peripheral vision is side vision and does not depend on the macula. Due to this fact, macular degeneration will never lead to total blindness.
The retina is the light-sensitive membrane of nerve tissue lining the back of the eye. It is the screen upon which images of the outside world are focused. At the center of the retina is the macula. The macula is no larger than a pinhead, yet it contains all of the visual cells needed for color vision and central vision. When the cells of the macula are damaged, it becomes difficult or impossible to see fine detail and to read a printed page.
There are two main types of AMD: dry and wet. Dry is the most common type. It tends to develop slowly, as the tissue beneath the macula gradually deteriorates. In wet AMD, tissue deterioration is accompanied by tiny abnormal blood vessels called subretinal neovascular membranes. These membranes form under the retina and leak fluid or bleed. If the blood or fluid reaches the macula and lifts it out of position, vision becomes distorted and visual sharpness is lost. Progression of wet AMD is usually much quicker than dry.
Scientists have not yet learned why a macula that has functioned well for 60 years suddenly degenerates. It is likely that many factors are involved including heredity, exposure to bright sunlight, and smoking. Smokers and former smokers have been found to have a much higher risk of AMD; quitting smoking does not seem to reverse the degeneration, or even slow it down. It is also possible that normal tissue changes associated with aging somehow interfere with the macula getting enough oxygen. One thing is certain; use of the eyes does not impact the development or progression of macular degeneration.
With either type of AMD, the first symptom is typically blurred vision. If the blurring is gradual, it may go unnoticed, or seem unimportant or unalarming. Perhaps only one eye is blurred, and the other eye is picking up the slack. As time passes, a hazy or dark area may develop in the center of objects. Colors may begin to look different or lose richness. With wet AMD especially, straight lines like the edges of doorways may appear bent or crooked. These symptoms can occur in one or both eyes, and can be gradual or sudden.
Deposits called drusen may build under the macula. Although drusen are often a normal and harmless sign of aging, they can be warning signs of degenerative macular changes beginning.
A complete eye examination, including dilation (enlargement) of the pupils, is necessary to diagnose and treat AMD. Eye drops are used to induce dilation. Without large pupils, the doctor may be unable to see inside the eye well enough to make a correct diagnosis. A special lens is often used to help examine the retina and macula. Also, fluorescein angiography may be recommended. Fluorescein angiography provides retinal photographs that are a useful tool in determining the extent of the problem and evaluating its progression. For the angiography, an orange-colored dye (fluorescein) is injected into a vein in the arm. A series of photographs is then taken as the dye travels through the eye's blood vessels. If further information is needed, a dye called indocyanine green may also be used.
AMD usually develops gradually over many months, then slows or stops. Both eyes are usually affected, although degeneration in one eye may precede the other by a long time, even years. Wet changes occur unpredictably; there is some chance they will develop even in dry AMD, or they may recur in previously treated wet AMD.
It is possible, even with no laser treatment, for the degenerative process to stop before very much vision has been lost. However, it is more likely that vision will continue decreasing, probably to the point that reading is hampered and driving a car is no longer safe. Legal blindness is a term used to describe vision that eyeglasses cannot correct to 20/200 (the large E on the standard eye chart). This term is merely a legal definition used to determine eligibility for certain social services and an extra income tax exemption.
Even if degeneration is severe, side vision will remain normal and can be relied upon for many regular tasks. It is important for people with AMD to learn to use the vision they have to its fullest, perhaps working with a low vision specialist. The low vision specialist works with a person to select magnification devices for seeing better in specific situations. This specialist can introduce non-optical aids as well, such as large-type books and magazines, press-on numbers for your appliances, and even talking clocks.
When caught in its early stages, vision damaged by wet AMD can sometimes be stabilized with laser treatment. Laser is used to seal leaks or destroy abnormal blood vessels growing under the macula. No matter how accurately it is performed, laser treatment involves some risk to vision. The laser can destroy normal tissue neighboring the abnormal tissue that is targeted. Due to this risk, laser is recommended only if the danger is small and there is a reasonable chance for success. Laser is generally not indicated if the degeneration is too extensive, too advanced, or in too critical a location
Major clinical research, including research being done here at the University Center for Vision Research, continues to look for new forms of AMD treatment and prevention. For example, certain antioxidants, vitamins and minerals are being studied as a way to slow degeneration. Scientific evidence for the effectiveness of these supplements remains inconclusive. Several national studies are evaluating the effect of radiation therapy to treat abnormal subretinal blood vessels. The results of this treatment also appear variable at this time. There are currently no medications that have been proven effective for treating AMD.
In addition to having regular eye exams, there is an easy and important test people with AMD should do at home. An Amsler grid is a card printed with a pattern of crossing lines that form small squares. People with AMD should use this grid daily to test each eye separately. The lines of the grid should look straight and solid. If lines look wavy or have missing segments, wet changes could be indicated, and the ophthalmologist should be informed immediately. Such early wet changes may be treatable, so an eye examination should be done within a day or two. To obtain an Amsler grid, contact the administrator of this web page at email@example.com.
Many people find it comforting to talk to others who share similar problems. Support groups are often an ideal place to exchange ideas, frustrations and successes. Visit The Foundation Fighting Blindness website for more information about support groups in your area.
Always keep in mind that use of the eyes will never harm them. People with AMD should continue all usual activities as long as they feel comfortable doing them. Reduced vision does not mean that life can not be surprisingly normal and fulfilling.
For more information or questions about Age-related Macular Degeneration, or a referral, contact the University Center for Vision Care and Research with the online Information Request Form:
The Center for Vision Care and Research
550 Harrison Street, Syracuse, NY 13202