Macular Degeneration
Macular degeneration is an incurable eye disease that is the leading cause of blindness in the United States. Macular degeneration affects more Americans than cataracts and glaucoma combined. Ten million Americans have macular degeneration with 1.6 million of those experiencing severe loss of vision. Macular degeneration has reached near epidemic levels in the United States. Since many people diagnosed with macular degeneration are over age 55, the number of cases of macular degeneration in the U.S. will increase significantly as baby boomers age.
Age-related macular degeneration is a chronic eye disease that occurs when tissue in the macula, the part of the retina responsible for central vision, deteriorates. The retina is the layer of tissue on the inside back wall of the eyeball. The macula is made up of densely packed light-sensitive cells called cones and rods. These cells, particularly the cones, are essential for central vision. Degeneration of the macula causes blurred central vision or a blind spot in the center of the visual field. The specific factors that cause macular degeneration are not conclusively known.
The first sign of macular degeneration may be a need for more light for close-up work. Fine newsprint may become harder to read and street signs more difficult to recognize. The straight lines of a grid may appear distorted or crooked. Gray or blank spots may mask the center of the visual field. The condition usually develops gradually, but may sometimes progress rapidly, leading to severe vision loss in one or both eyes.
Macular degeneration affects central vision, but not peripheral vision; thus it doesn’t cause total blindness. Still, the loss of clear central vision — critical for everyday activities such as reading, driving, recognizing people’s faces and doing detail work — greatly affects quality of life. In most cases, the damage caused by macular degeneration is irreversible, but early detection may help reduce the extent of vision loss.
Macular degeneration usually develops gradually and painlessly. The signs and symptoms of the disease may vary, depending on which of the types of macular degeneration.
Types of Macular Degeneration
Macular degeneration occurs in two types:
Dry macular degeneration-Most people with macular degeneration have the dry form. In fact, macular degeneration almost always starts out as the dry form. The dry form may initially affect only one eye but, in most cases, both eyes eventually become involved.
In a normal eye, the light-sensitive cells of the macula continuously shed used-up outer segments as waste. At the same time, cones and rods continuously produce new outer segments to replace the discarded ones. In dry macular degeneration, the waste disposal system fails. Aging slows the process to a point where waste starts to accumulate. This accumulation causes the light-sensitive cells of the macula (both cones and rods) to degenerate.
Dry macular degeneration causes the following symptoms:
- The need for increasingly bright illumination when reading or doing close work.
- Increasing difficulty adapting to low light levels.
- Printed words that appear increasingly blurry.
- Colors that appear less bright.
- Difficulty recognizing faces.
- A gradual increase in haziness of overall vision.
- A blurred or blind spot in the center of the visual field combined with a profound drop in central vision acuity
- A need to scan an object to provide a more complete image
Wet macular degeneration: While it accounts for only about 15 percent of all cases, wet macular degeneration is responsible for the most severe vision loss. Developing wet macular degeneration in one eye greatly increases the odds of developing it in the other eye. Almost everyone with wet macular degeneration develops dry macular degeneration first.
Wet macular degeneration develops when new blood vessels grow underneath the macular portion of the retina. These vessels leak fluid or blood; hence the name “wet” macular degeneration. Central vision blurs and straight lines appear wavy or crooked. With the wet form of macular degeneration, sight loss is usually rapid and severe, resulting in legal blindness (defined as 20/200 vision or worse).
Wet macular degeneration causes the following symptoms, which may progress rapidly:
- Visual distortions, such as straight lines appearing wavy or crooked, a doorway or street sign that seems out of whack, or objects appearing smaller or farther away than they should.
- Decrease in or loss of central vision.
- A central blurry spot.
Another form of wet macular degeneration, called retinal pigment epithelial detachment (PED), occurs when fluid leaks even though no abnormal blood vessels have started to grow. The fluid collects under the retinal pigment epithelium, causing what looks like a blister or a bump under the macula. This kind of macular degeneration causes similar symptoms to wet macular degeneration, but visual acuity may remain relatively stable for many months or even years before it deteriorates. This form of macular degeneration usually progresses to the more common wet form of macular degeneration that includes newly growing abnormal blood vessels.
In either the dry or wet form of macular degeneration, the vision initially may falter in one eye but not the other. Since the good eye often compensates for the weak one, the symptoms of macular degeneration may not be recognized at its early stages. Vision and lifestyle are dramatically affected when macular degeneration develops in both eyes.
More information about macular degeneration can be found at www.nei.nih.gov and www.macular.org.
