Information About Age-Related Macular Degeneration

Information courtesy of "The U.S. Foundation Fighting Blindness"

Age-related macular degeneration (AMD) is a retinal degenerative disease that causes a progressive loss of central vision. AMD is the most common cause of vision loss in individuals over the age of fifty. It is estimated that over six million Americans have this disease.

Clinical description

Central vision loss from AMD is caused by the degeneration of the macula. The macula is the central portion of the retina responsible for perceiving fine visual detail. Light sensing cells in the macula, known as photoreceptors, convert light into electrical impulses and then transfer these impulses to the brain via the optic nerve. Central vision loss from AMD occurs when photoreceptor cells in the macula degenerate.

Individuals with AMD may first notice a blurring of central vision that is most apparent when performing visually detailed tasks such as reading or sewing. Blurred central vision may also make straight lines appear slightly distorted or warped. As the disease progresses, blind spots form within central vision. In most cases, if one eye has AMD, the other eye will also develop the disease. The extent of central vision loss varies according to the type of AMD.

Dry AMD

There are two types of AMD: 'dry' and 'wet'. Dry AMD accounts for about 90 percent of all cases. Dry AMD is sometimes called atrophic, nonexudative, or drusenoid macular degeneration. With dry AMD, yellow-white deposits called drusen accumulate in the retinal pigment epithelium (RPE) tissue beneath the macula. Drusen deposits are composed of waste products from photoreceptor cells. For unknown reasons, RPE tissue can lose its ability to process waste. As a result, drusen deposits accumulate in the RPE. Drusen deposits are typically present in patients with dry AMD. These deposits are thought to interfere with the function of photoreceptors in the macula, causing progressive degeneration of these cells. Drusen deposits can, however, be present in the retina without vision loss.

Vision loss from dry AMD occurs very gradually over the course of many years. Central vision may even remain stable between annual eye examinations. Individuals with AMD do not usually experience a total loss of central vision. However, vision loss may make it difficult to perform tasks that require finely focused vision. Although there are extensive research efforts to find treatments for dry AMD, at this time no proven treatments exist.

Wet AMD

Wet AMD accounts for about 10 percent of cases. Wet AMD is also called choroidal neovascularization, subretinal neovascularization, exudative, or disciform degeneration. In wet AMD, abnormal blood vessel growth forms beneath the macula. These vessels leak blood and fluid into the macula damaging photoreceptor cells. Wet AMD tends to progress rapidly and can cause severe damage to central vision.

In some cases, if wet AMD is diagnosed early, laser surgery can prevent extensive central vision loss. In this type of surgery, laser beams destroy the leaky blood vessels that form beneath the macula. For laser surgery to be effective, it is critical that wet AMD be diagnosed before extensive vision loss occurs. Therefore, individuals should consult with an eye doctor at the first sign of blurred or distorted central vision. Doctors are also conducting clinical trials to test experimental treatments. If you are diagnosed with wet AMD, you may want to ask your doctor about these treatments.

Diagnosis

Along with regular examinations by an eye doctor, individuals can test their eyesight for possible symptoms of AMD with a simple home test known as the Amsler grid. The Amsler grid, consisting of parallel and perpendicular lines, looks much like a sheet of graph paper. By focusing on a marked spot in the middle of the grid, one can assess whether the lines appear blurred or distorted. While the Amsler grid is not a substitute for expert medical diagnosis, it does allow individuals to check their eyesight regularly for possible symptoms of AMD. To receive a free Amsler grid, please call the Foundation Fighting Blindness.

Risk factors

The causes of both dry and wet AMD are not well understood. Scientists are currently examining whether genetic inheritance, diet, cigarette smoking, light exposure, cardiovascular disease and hypertension are significant risk factors for AMD.

Inheritance

When a disease like AMD occurs late in life, scientists often have difficulties finding enough surviving family members to determine whether the disease is genetically inherited. Initial studies have found an increased incidence of AMD among family members of patients with the disease.

Recently, Foundation-supported researchers mapped a gene causing an autosomal dominant form of age-related macular degeneration (AMD) to human chromosome 1. Gene mapping is the process of identifying which of the 23 paired chromosomes contains a gene with disease-causing mutations.

While further work is needed, these studies indicate that genetic inheritance plays a role in the disease.

Nutrition

Scientists are conducting large-scale studies to determine whether nutrition might play also a role in preventing or minimizing vision loss from AMD. Preliminary data from one such study suggest that diets high in saturated fats and cholesterol may increase the risk of developing AMD. Preliminary data from another study suggest that diets rich in green, leafy vegetables may be helpful in reducing the risk of AMD. A third study is evaluating whether antioxidants can prevent or minimize AMD by protecting the retina from damage associated with light exposure. Antioxidant vitamins and minerals such as C, E, carotenoids, selenium and zinc are found in many fresh fruits and vegetables.

Although research has not yet established a clear benefit for antioxidants in the fight against AMD, vitamin companies have begun marketing antioxidant supplements claiming they may prevent or slow the disease. However, it is not known whether supplements confer the same nutritional benefits as do food sources rich in antioxidants. Moreover, large doses of antioxidant supplements can have detrimental health effects. Ongoing studies must show that antioxidants are effective in preventing or slowing the progression of AMD before dietary recommendations can be made.

Individuals with AMD should discuss dietary considerations with their doctor.

Low-vision aids

As central vision declines, individuals with AMD may benefit from the use of low-vision aids. Low-vision aids such as magnifying glasses and special lenses can optimize existing peripheral vision.

Computerized reading machines and print enlargers enable individuals to read small print. Low-vision specialists can also help individuals adapt daily living skills. Low-vision specialists are available through ophthalmology centers and physician referrals.

For more information contact:

Retina New Zealand inc.
P.O. Box 27 177
Wellington
NEW ZEALAND

Tel: [04] 389 1538
Fax: [04] 389 5254
Email: retinanz@ihug.co.nz