What Is Macular Degeneration?
Age-related macular degeneration (AMD, or just macular degeneration) is a common eye disease associated with aging. It blurs the sharp, central vision you need for "straight-ahead" activities, such as reading, sewing, and driving. In some people, macular degeneration advances so slowly that it has little effect on their vision as they age. But in others, the disease progresses faster and may lead to a loss of vision in one or both eyes.
About 1.7 million Americans have some form of macular degeneration. It is the leading cause of vision loss among Americans ages 65 and over.
In order to understand macular degeneration, it is helpful to understand the parts of your eye involved with sight. These structures include the cornea, iris, pupil, lens, macula, and retina.
Your cornea is a thin, clear layer on the outside of your eye. The iris, or the colored part of your eye, is a muscle that controls the amount of light going through your pupil, which is the round opening in the center of your eye. Behind the iris sits the lens, which is just larger than your pupil. The iris is enclosed by a thin, clear capsule that holds the lens in its proper place.
When light enters your eye, the cornea and lens form the light rays into a beam of light that is focused directly onto your retina -- the light-sensitive tissue at the back of the eye. The retina instantly converts light, or an image, into electrical impulses. The retina then sends these impulses, or nerve signals, to the brain through the optic nerve. The optic nerve is a bundle of more than one million nerve fibers connecting the retina to the brain.
The macula is located in the center of the retina. It is made up of millions of light-sensing cells that help to produce central vision.
Types of Macular Degeneration
There are two types of macular degeneration. About 90 percent of people with macular degeneration have what's known as the "dry" type, and the remaining 10 percent have the "wet" type. However, the wet type accounts for 90 percent of all blindness from the disease.
In
wet macular degeneration, new blood vessels grow. Because these new blood vessels tend to be very fragile, they will often leak blood and fluid under the macula. This causes rapid damage to the macula, which can lead to the loss of central vision in a short period of time.
In
dry macular degeneration, the light-sensitive vision cells deteriorate, but there is no bleeding. Scientists are still not sure what causes dry macular degeneration. Studies suggest that an area of the retina becomes diseased, leading to the slow breakdown of the light-sensing cells in the macula and a gradual loss of central vision.
No one knows exactly what causes macular degeneration, and doctors can seldom explain why one person gets it and another does not. However, research has shown that people with certain risk factors are more likely than others to develop macular degeneration. A risk factor is anything that increases a person's chance of developing a disease.
Specific risk factors of macular degeneration include:
(Click Causes of Macular Degeneration for more information.)
Macular degeneration rarely leads to complete blindness, but often causes severe and irreversible loss of central vision. Side vision remains, but the center of vision, which is needed for daily tasks like reading and driving, is destroyed.
Common symptoms include:
- Blurry vision
- Seeing straight lines as crooked or wavy
- A dark, empty area appearing in the center of vision
- Drusen, which are yellow deposits under the retina.
Pain is not a symptom of macular degeneration.
In order to make a diagnosis, your doctor will ask you a number of questions about your medical history and will also perform a comprehensive eye exam.
- Visual acuity test
- Dilated eye exam
- Tonometry
- Amsler grid
- Fluorescein angiogram.
(Click Diagnosing Macular Degeneration for more information.)
Treatment for Macular Degeneration
There is no cure for macular degeneration. Treatment options depend on the type of macular degeneration.
Your doctor can describe your treatment options and the expected results of each. You and your doctor can work together to develop a treatment plan that meets your medical needs and personal values. Choosing the most appropriate treatment for macular degeneration is a decision that ideally involves the patient and health care team.
