Macular degeneration, often referred to as age-related macular degeneration (ARMD or AMD), is the leading cause of blindness in the United States. ARMD primarily affects people aged 65 and older. Some macular complications that affect younger people are sometimes referred to as macular degeneration, but the term generally refers to age-related macular degeneration. The part of the eye affected by ARMD is the macula, the sensitive part of the retina responsible for sharp, central vision.
Vision loss in early cases of macular degeneration is so gradual that most people do not notice it. Pain is not usually experienced. As the disease progresses, vision may be blurred and objects may appear distorted. Patients may complain of missing letters in words or difficulty seeing smaller print. In more severe cases of AMD, there may be a profound loss or graying of central vision, while peripheral vision remains unchanged. Furthermore, color vision may be altered.
Macular degeneration is related to advancing age. Although one’s environment may contribute to the development of AMD, current research is focusing on certain genes that some individuals possess which may increase or decrease their risk for developing AMD. In macular degeneration, a noticeable change occurs in the pigmented cells in the macula. Cellular debris begins to build up, producing yellow or white particles known as drusen. In some cases, a perceived lack of oxygen in the retina signals chemical mediators to begin new blood vessel growth, or "neovascularization." The new blood vessels are weak and may leak fluid and blood into the retinal tissue.
In addition to age, there are several known risk factors for developing age-related macular degeneration:
- Light eye color
- White ethnicity
- Cardiovascular disease
- Family history
- Female gender
- Sun exposure
There are two major types of age-related macular degeneration, "dry" macular degeneration and "wet" macular degeneration.
- Dry (non-neovascular) AMD:
Dry AMD is the most common type and accounts for about 90 percent of all AMD cases. In dry AMD, an observable change in the pigmented cells occurs, leaving areas of depigmentation, pigment clumping and drusen. Dry AMD usually progresses very slowly. Amount of vision loss varies but rarely progresses to legal blindness. Some patients may develop macular tissue atrophy and mild scarring.
- Wet (neovascular) AMD:
Wet AMD accounts for approximately 10% of all AMD cases. Patients with the dry form of AMD may progress to the more severe, wet form. New blood vessel growth (neovascularization) occurs underneath the retina. Although these vessels are new, they are frail in nature. As the name implies, the appearance is wet: blood and fluid leak out of the new blood vessels, causing permanent tissue damage. Scarring may occur, causing significant loss of vision and many times, legal blindness.
The diagnosis of AMD is made after a comprehensive eye examination is performed by an optometrist or ophthalmologist. Both distance and near vision is measured. In addition, a test called an "Amsler grid" is performed to locate blind spots, waving lines or distortions in vision. A dilated retinal exam will also take place. This allows the doctor to see a magnified view of the macula. If AMD is suspected, a dye-injection test, called fluorescein aniography (FA), may be ordered. Another diagnostic test, called optical coherence tomography (OCT), may also be performed. If AMD is detected, the patient is referred to a retinal specialist.
There is no known cure for macular degeneration. Treatment focuses on delaying or lessening the progression of the disease and varies depending on the stage of the disease that exists. Based on the Age-Related Eye Disease Study (AREDS) completed in 2001, nutritional supplements containing vitamins C and E, beta-carotene and zinc were shown to slow or delay the progression of dry AMD to advanced AMD by 28% in certain patients.
Treatment for wet AMD focuses on stopping the fluid leakage from neovascularization. Procedures such as "photocoagulation" and "macular translocation" have been performed in the past with variable results. More recently, anti-vascular endothelial growth factor (anti-VEGF) medications are being used for treatment of macular degeneration. These drugs are injected directly into the eye and act to stop new blood vessels from forming.
For patients with significant vision loss, low vision centers and doctors can recommend certain products or home modifications that can give back functional vision and improve quality of life. Some of these devices include high-powered reading glasses or bifocals, telescopic lenses, hand-held devices, magnifiers and closed-circuit televisions. Other recommendations, such as using large numbered clocks and stove dials, large print books, writing templates and electronic talking devices, may dramatically increase a macular degeneration patient’s quality of life.