Macular degeneration

Definition
Macular degeneration is a breakdown of the macula that causes impaired vision.

Anatomy
The macula is a small area in the center of the retina (the light-sensitive tissue at the back of the eye that sends nerve impulses to the brain). The macula is responsible for central (straight ahead) vision. The macula also controls the sharp, detailed vision needed for close-up tasks, such as reading fine print or threading a needle.



Causes/associated factors
Aging is the most common cause of macular degeneration. In fact, age-related macular degeneration is a leading cause of irreversible vision loss for older Americans. The risk is higher among women, Caucasians, smokers and those who have high cholesterol levels. Injuries, infection or inflammation can also affect the macula. Sometimes the condition is inherited.

Types of age-related macular degeneration
There are two forms of age-related macular degeneration (AMD): dry and wet. About 90 percent of people with AMD have the dry type. It is considered less severe than the wet type, and the visual loss is gradual. Dry macular degeneration is caused by aging and thinning of the tissues of the macula. It often occurs in just one eye at first, but both eyes may eventually be affected. There is no way to determine if or when both eyes will develop the condition.
About 10 percent of people with AMD have the wet variety. It's considered the more severe form and is responsible for most cases of severe vision loss due to macular degeneration. Wet macular degeneration is associated with abnormally fragile blood vessels at the back of the eye. Eventually, these blood vessels leak fluid or bleed. The result can be rapid or severe vision loss. With time, the blood vessels grow and create scar tissue. Once the eye is scarred, vision loss is permanent.

In some cases, dry macular degeneration becomes the wet variety. The odds of this happening are greatest if the wet form is present in one eye and the dry form in the other.


Signs/symptoms
Symptoms of macular degeneration may be unique for each person. Peripheral (side) vision isn't usually affected, and the condition is often painless. Sometimes only one eye loses vision, and the condition may be barely noticeable at first. Possible symptoms include:
blurred vision that may go away in brighter light
a small but growing blind spot, sometimes described as a dark empty area or "whiteout" in the middle of a person's field of vision
straight lines may appear crooked
object distortion
dimmed color vision
trouble reading or with close-up tasks, especially if both eyes are affected
Remember, the symptoms of macular degeneration appear gradually. If you experience any sudden visual loss, consult your doctor immediately.


Diagnosis
Early detection and diagnosis are important. The first step is to check your vision. Here's what to expect during a medical eye exam:
Visual acuity will be tested to determine how well you see at various distances.

After using eyedrops to dilate (enlarge) your pupils, the doctor will examine the inside of your eyes with an instrument called an ophthalmoscope. Dilating your pupils gives the doctor a better view of the retina. Your eyes will be checked for drusen, small yellow deposits in the retina that may signify macular degeneration.

The doctor will use a test called tonometry to measure the fluid pressure in your eyes.

Next, you'll look at an Amsler grid, which looks like a checkerboard. The doctor will ask you to cover one eye and look at a black spot in the middle of the grid. If you have wet macular degeneration, the straight lines of the grid may look wavy to you.

Fluorescein angiography can help doctors confirm a diagnosis of wet macular degeneration. First, dye is injected into your arm. Then special photographs are taken as the dye passes through the blood vessels in the back of your eye. The photos help doctors find abnormal blood vessels under the retina.

If that test doesn't work, another dye test called indocyanine green angiography can also be done. This test identifies hidden blood vessels that grow underneath the retina.

Treatment
Despite ongoing research, there is no cure for either type of macular degeneration.
There is no specific treatment for dry macular degeneration. Researchers have found that taking supplemental antioxidants and zinc can slow down the progression of dry macular degenerative changes, however. Discuss nutritional supplements with your doctor before adding them to your diet.

Consider using visual aids to enhance your remaining vision. Magnifying lenses and tiny telescopes or microscopes mounted onto conventional eyeglasses can be helpful. Closed-circuit television, large-print materials and special lighting can also minimize the effects of visual impairment. Specialized training from low-vision specialists can help people who have macular degeneration make the most of their peripheral vision and learn to function with impaired central vision.

For some cases of wet macular degeneration, laser surgery can seal the leaking blood vessels that damage the macula. It can't cure the condition, but it can slow the rate of vision loss. Laser surgery leaves a small blind spot at the point of laser contact. The procedure can save more sight than is lost, however. During follow-up exams, the doctor makes sure the blood vessels have been sealed completely and checks for the growth of new blood vessels.

Photodynamic therapy (PDT) is a newer treatment that combines laser surgery with the medication verteporfin (brand name Visudyne). First, the medication is injected into your bloodstream. Then, you receive a laser treatment. This combination helps destroy abnormal blood vessels that damage the macula.

Other approaches being studied include low-dose radiation to shrink abnormal blood vessels, cell transplantation and the use of interferon (a drug that fights infections and tumors). Discuss these alternatives with your ophthalmologist.


Complications
Untreated wet macular degeneration can lead to irreversible blindness. Rarely, the fragile blood vessels can create a hemorrhage that causes sudden vision loss. When wet macular degeneration is treated with laser surgery, new blood vessels that also require treatment may grow back in a significant percentage of the treated areas.

Pregnancy-specific information
Pregnancy is not a risk factor for macular degeneration.

Senior-specific information
Age-related vision changes are common. People in their 50s have a 2 percent chance of developing macular degeneration. For those over age 75, the odds jump to 30 percent.

Prevention
If you're over age 50, be alert to any signs of possible macular degeneration. Learn the warning signs, and visit your eye doctor if you experience any of the symptoms. Yearly eye exams by an ophthalmologist are recommended for people over age 60, or earlier for those who have a family history of retinal problems.
To catch vision changes as early as possible, you may want to use an Amsler grid at home. You can also help to reduce your risk by controlling high blood pressure and avoiding high-cholesterol foods. If you smoke, quit. Finally, wearing sunglasses that block ultraviolet light may slow macular degeneration as well.