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What Is Macular Degeneration?
Macular degeneration is a condition that damages the macula, the central part of the retina. The macula is responsible for central vision and the ability to see detail.
When the macula is damaged, the eye loses its ability to see detail, such as small print, facial features or small objects. The damaged parts of the macula often cause scotomas, or localized areas of vision loss. When you look at things with the damaged area, objects may seem to fade or disappear. Straight lines or edges may appear wavy.
What Are the Different Types of Macular Degeneration?
There are two types of the disease: dry macular degeneration and wet macular degeneration.
Dry macular degeneration
Ninety percent of people who have macular degeneration have the dry form of the condition. In dry macular degeneration, waste products may accumulate in the tissues underneath the macula forming yellowish deposits called drusen.
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.
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.
Symptoms
Both the dry and wet form of AMD cause no pain. The most common early sign of dry macular degeneration is blurred vision. As fewer cells in the macula are able to function, people will see details less clearly in front of them, such as faces or words in a book. If the loss of these light-sensing cells becomes great, people may see a small -- but growing -- blind spot in the middle of their vision.
The classic early symptom of wet macular degeneration is that straight lines appear crooked. This occurs when fluid from the leaking blood vessels gathers and lifts the macula, distorting vision. A small blind spot may also appear in wet macular degeneration, resulting in loss of one's central vision.
Diagnosis
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.
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. Several tests are performed to assess your vision combined with examination of the internal structures of the eye after dilation of the pupil.
Testing Detail Vision: Visual Acuity Test
Your eye exam will typically begin with a visual acuity test. This test checks the sharpness of your vision by measuring accurate vision without correction, as well as best corrected vision confirmed by refraction. You may read black letters of varying sizes to determine how well you see at various distances.
Testing the Macular Area: Amsler Grid
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.
Examining the Inside of the Eye: Ophthalmoscopy
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.
Taking Pictures of the Retina: Angiography
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 takes 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.
Risk Factors
While there are no known causes of macular degeneration, many studies have been performed which illustrate factors that may put you at risk for the disease. There are risk factors you can't control, such as age and genetics, and risk factors that you can control, such as smoking and poor nutrition.
Risk Factors You Can't Control
- Age
- Race (Caucasians are at greater risk)
- Genetics
- Light eye color
Risk Factors You Can Control
- Smoking
- High blood pressure
- High cholesterol
- Poor nutrition
- Unprotected exposure to sunlight
- Excessive sugar and trans fats intake
- Obesity
- Sedentary lifestyle
An unhealthy lifestyle, which may include smoking, poor nutrition or limited exercise, could contribute to your risk of developing macular degeneration. As a result, many risk factors are within your control to reduce your chance of getting the disease and to promote better health.
What You Can Do to Reduce Risk
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.
- 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 have already been diagnosed with the disease.
Treatment
There are currently no medical or surgical treatments for dry AMD, though there are two clinically proven treatments for wet AMD.
1. Photocoagulation
A surgical procedure involving the application of a hot laser to seal and halt, or slow, the progression of abnormal blood vessels. This procedure may produce a blind spot on the retina.
2. Photodynamic therapy
A treatment that uses a non-thermal (cold) laser with an intravenous, light sensitive drug to halt, or slow, the progression of abnormal retinal blood vessels. This treatment does not leave a blind spot on the retina.
Early Detection
People under 50 should have an eye exam every three to five years. People with a family history of eye conditions or those with a medical condition associated with eye disease, such as diabetes, should have their eyes tested every year, particularly if they are over 65. If you notice changes in vision -- vision becomes blurry, for example -- visit your eye doctor immediately.
Once vision is lost due to the growth of abnormal blood vessels, it cannot be restored. Early detection and treatment of AMD can significantly increase the chances of an independent lifestyle.
Sources: Vision Australia, Lighthouse International and the National Eye Institute, National Institutes of Health