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More on Macular Degeneration
Despite the fact that macular degeneration is the leading cause of vision loss in people over 60, many know very little about the disease. Because macular degeneration mainly affects older adults, the disease is frequently referred to as Age-Related Macular Degeneration (AMD). While central vision may deteriorate with macular degeneration, side, or peripheral, vision remains intact. What follows: facts about the disease, warning signs, reducing your risk, treatments and information on vision rehabilitation that can help you cope with the changes that macular degeneration brings.
Facts About Macular Degeneration
- Approximately 25-30 million people around the world are affected by some form of Age-Related Macular Degeneration[1].
- One new case of macular degeneration is diagnosed every three minutes in the United States[2].
- People rarely become totally blind from macular degeneration. Since the disease affects only central vision, side vision remains. The loss of central vision, however, can make it difficult to read, drive or perform activities that use detailed, central vision.
What Is Macular Degeneration?
Before answering this question, it is helpful to be familiar with the eye and, in particular, the macula.
What Is the Macula?
The macula is the central area of the retina - the thin, light-sensitive tissue lining the back of the eye. The retina converts light patterns into nerve signals that tell the brain what you are seeing. The macula controls your central vision. Central vision enables you to do activities that require you to see detail, such as reading, driving, watching television and recognizing faces. The macula is also responsible for color and daylight vision.
The millions of cells in the macula use energy and nutrients to process images while also generating waste products. Most of the nutrients used by the macula are supplied by blood vessels from the layer under Bruch's Membrane called the choroid. The choroid is the layer of blood vessels beneath the retina.
In a healthy eye, nutrients from the choroid pass through Bruch's membrane to reach the cells in the macula, as waste products travel from the cells of the macula back to the blood vessels to be flushed away.
What Are the Different Types of Macular Degeneration?
Dry Macular Degeneration
In dry macular degeneration, waste products may accumulate in the tissues underneath the macula forming yellowish deposits called drusen.
- On their own, scattered drusen are not harmful and many people with drusen will not progress to the later, more serious, stage of the condition.
- When drusen have been noted in an eye exam, the doctor will monitor the condition and may order further testing.
- Some people with drusen may begin to experience mild vision loss.
The continued presence of drusen interferes with the blood flow to the retina and, in particular, to the macula. Less blood flow reduces the nourishment to the macula causing its light sensitive cells to stop working efficiently, or atrophy. You will sometimes hear dry macular degeneration referred to as atrophic macular degeneration.
Occasionally, a large area of cells will stop working. This is called geographic atrophy, which produces a distorted or blind spot, also known as a scotoma, in the central area of vision.
- 90 percent of people who have been diagnosed with macular degeneration have the dry form of the disease.
- The dry form progresses slowly and does not lead to rapid, severe vision loss.
- People who have dry macular degeneration may experience a gradual loss of detail vision.
Wet Macular Degeneration
Though the wet form of macular degeneration affects only 10 percent of people diagnosed with the disease, it accounts for almost 90 percent of the severe vision loss associated with the condition. Dry form patients who have large drusen without clear borders or who have many drusen that run together are at greater risk for developing the wet form of the disease.
With wet macular degeneration, new weak blood vessels may grow in or under the retina causing fluid and blood to leak into the space under the macula. As a result, wet macular degeneration is sometimes called exudative macular degeneration. (An "exudate" is material, such as fluid, which has escaped from blood vessels and has been deposited in tissues.)
You may also hear wet macular degeneration described as choroidal neovascularization. The choroid is the area of blood vessels beneath the retina and neovascularization refers to growth of new blood vessels in tissue. In choroidal neovascularization, blood vessels from the choroid grow into the macula.
The two main types of the wet form of macular degeneration are classic choroidal neovascualrization and occult choroidal neovascularization. In both, blood vessels grow into the macula.
Progression of Wet Macular Degeneration
In the later stages of wet macular degeneration, the continued growth of blood vessels combined with constant leakage can cause scarring of the macula. This is the last stage of the disease and often leads to significant loss of central vision. Side, or peripheral, vision will remain since damage is predominantly limited to the macula. Treatments for wet macular degeneration have been shown to slow or stabilize vision loss.
What Are the Warning Signs of Macular Degeneration?
Warning Signs: Dry Form
The most common warning sign of dry macular degeneration is blurred or distorted vision that may increase over a period of months or years, particularly in the central part of vision.
- You may need more light for reading and other tasks as the eye loses its ability to see detail.
- Color vision may also be reduced.
- In the later stages of the dry form, the damaged parts of the macula often cause localized areas of vision loss, or scotomas. Scotomas produce blurred spots, blank spots, blotches or distortion.
When you look at things with a damaged macula, objects may seem to fade or disappear. Over time, spots or blotches may darken or increase in size, causing deterioration of central vision.
People with dry macular degeneration may not even be aware that they have the disease, since changes in vision with the dry form can be very subtle. You may still see clearly and be able to perform tasks such as reading, driving, and watching television without difficulty. You may notice changes in vision only if both eyes are affected with the disease. It is important to get regular eye examinations to check for the disease even if you do not notice any warning signs.
Warning Signs: Wet Form
- In wet macular degeneration, objects may appear wavy or distorted. For example, the straight edge of a building may appear to be curved. This is due to blood vessels leaking fluid under the retina, causing the surface of the macula to become elevated and swollen.
- Another warning sign of the wet form is a sudden and rapid decrease in central vision.
- Blind spots may also appear if blood vessels break through the surface of the retina or cause leakage of blood (hemorrhage).
How Is Macular Degeneration Diagnosed?
Regular eye exams are the key to early detection of macular degeneration since symptoms may or may not be present in people who have the disease. Early drusen can be seen in an eye exam before symptoms develop, so you should visit your eye care professional regularly.
If you notice any of the warning signs described in the previous section, or if you begin to experience difficulty:
- recognizing faces,
- reading (print looks fragmented or distorted and colors appear muted),
- watching TV (image is blurry or parts of image are obstructed),
- seeing street or highway signs when driving
call your eye doctor immediately.
Eye Exam
During the eye exam, your eye doctor will inquire about any eye problems you may be having as well as your general medical and family history. He or she will typically perform several tests to assess your vision and then examine the internal structures of the eye. These include:
Your eye exam will typically begin with a visual acuity test. This test checks the sharpness of your detail vision. You may be asked to read black letters of varying sizes to determine how well you see at various distances.
Your doctor may test your macular area with an Amsler grid. The Amsler grid resembles a piece of graph paper (black lines on white background or vice versa) with a dot in the middle. Using the grid is one of the best methods of detecting areas of distorted, blurred or reduced vision -- common symptoms of macular degeneration.
Your doctor will ask you to cover one eye and stare at the dot in the center. If some lines of the grid appear wavy or distorted, or if certain lines are missing, these are signs of macular degeneration.
Some doctors may also provide an Amsler grid to take home so you can monitor your vision on a regular basis.
In the office, the doctor may also perform a macular visual field test, which is an automated visual field test for the macula only.
The procedure known as ophthalmoscopy allows the doctor to view the back of the eye (retina) to look for signs of macular degeneration. Before this portion of the exam, you may receive drops in your eyes to widen, or dilate, your pupils so it is easier to view the retina.
The doctor will look for the presence of drusen as well as other abnormal areas of the retina.
If the doctor suspects that you have macular degeneration, you may need an additional test called angiography. This test - most useful in determining whether you have the wet or dry form of the disease - is not painful.
During the test, a special dye, either fluorescein or ICG (Indocyanine green), is injected into a vein in the arm. Once the dye reaches the eye, the doctor will take pictures of the retina to document the pattern of blood vessels and whether dye leaks from the vessels. The doctor can determine which areas of the macula are damaged and whether there are abnormal blood vessels to be treated.
What Happens Once You Have Been Diagnosed?
Vision loss for patients with wet or dry macular degeneration will depend on the location and extent of damage to the macula. The dry form is a slowly progressive chronic disease that may not develop into a more severe form and, as a result, can allow you to maintain your vision for a significant period of time. With current treatments available to slow or stabilize the wet form, you can anticipate longer periods of stable vision.
Once you have been diagnosed with macular degeneration, there is much that can be done. The first thing to remember is that side, or peripheral, vision remains useful in both the dry and wet form. As a result, you will be able to use your side vision to assist you even if your central vision diminishes.
How Can You Reduce the Risk of Developing Macular Degeneration?
You can lessen the risk of developing macular degeneration by reducing risk factors within your control, such as smoking and high blood pressure. You are never too young to reduce your risk for disease, so, no matter what your age, you can incorporate the following guidelines into your life.
Guidelines for Reducing the Risk of Macular Degeneration
- Quit smoking.
- Control high blood pressure.
- Control cholesterol level.
- Control cardiovascular disease.
- Improve nutrition
- Wear 100% UV protective sunglasses.
- Curb sugar intake.
- Maintain ideal body weight.
- Exercise regularly.
By following these guidelines, you not only may reduce your risk of developing macular degeneration, but you may also be able to stabilize or slow the effects of vision loss if you already have been diagnosed with the disease.
Regular Eye Exams
Early detection of macular degeneration gives you the best options for successful treatment and stabilization of the condition in the future. You should have regular eye exams with an ophthalmologist or optometrist for early detection of the disease. If you have already been diagnosed with macular degeneration, it is important to continue regular eye exams to monitor the condition, and to check for other conditions such as glaucoma and cataracts. If you experience any sudden vision changes, contact your doctor immediately.
By Eleanor E. Faye, MD, FACS; Michael Fischer, OD, FAAO; Sarah Lloyd; Karen Seidman, MPA; Cynthia Stuen, DSW
[1] Source: AMD Alliance International
[2] Source: Macular Degeneration Foundation
[3] Source: National Eye Institute, National Institutes of Health