Nearly 2 million Americans ages 40 and older are affected by age-related macular degeneration (AMD), which is a leading cause of vision loss in older adults, according to estimates from the Centers for Disease Control and Prevention (CDC). This eye disorder is more likely to occur after age 60, but it can occur at earlier ages.
Also called macular degeneration, AMD causes damage to the macula, the part of the eye needed for sharp, central vision, meaning the ability to view objects that are straight ahead. Central vision is needed for seeing objects clearly and for doing such common activities as driving, reading, writing, cooking, dialing a phone and recognizing faces.
Macular degeneration is deterioration in the central area of the retina, called the macula, said Dr. Mark Fromer, an ophthalmologist and retina specialist at Lenox Hill Hospital, in New York City.
The macula is located in the center of the retina, the inside back layer of the eyeball that converts light and images into electrical signals that get sent to the brain. AMD can occur in one or both eyes, and it usually does not affect peripheral (side) vision.
The eye disorder is more common among people as they get older. AMD typically develops gradually and isn't painful, so early symptoms can be mistaken for normal age-related vision changes. In other people, the disease progresses more quickly, and may lead to vision loss in one or both eyes.
"If a patient notices any distortion in one eye, he or she should see an ophthalmologist immediately," Fromer told Live Science. Visual distortions may include the symptoms described below.
According to the Mayo Clinic, symptoms of AMD include:
- Straight lines or faces appearing wavy
- Doorways seeming crooked
- Objects appearing smaller or farther away
- Increasing difficulty adapting to low light levels
- Decreasing color intensity or brightness
- Difficulty recognizing faces
- Increasing vision haziness
- Blurry or blind spots in central vision
- Causes & risk factors
The exact causes of AMD aren't known, but the risk of developing macular degeneration can increase with age. Genetics, certain physical conditions and lifestyle habits can also play a role. According to the National Eye Institute (NEI), these risk factors include:
- Being age 65 and older (but it can occur earlier)
- Family history of AMD
- High blood pressure
- High cholesterol
- Being Caucasian
- Being female
- Having blue eyes
- Diet low in fruits and vegetables
There are two types of AMD: wet and dry.
Dry AMD (also called geographic atrophy) is the most common form of macular degeneration affecting about 80 percent of people with AMD. It generally affects both eyes and its symptoms progress slowly. Dry AMD occurs when light-sensitive cells in the macula gradually deteriorate. Yellow deposits of protein, called drusen, form behind the retina. Drusen can dislodge the macula from its usual location in the eye. The size and number of drusen often indicate how severe dry AMD has become. Most people develop very small drusen as they get older, but when drusen are numerous or large, dry AMD is usually more advanced, according to the NEI. Changes in the pigment of the retina can also be a sign of the disease.
Wet AMD (also called neovascular AMD) is the less common form, occurring in only about 10 to 15 percent of all cases, but it is more serious than dry AMD and can trigger rapid vision loss, according to the NEI. It develops when abnormal blood vessels grow underneath the retina and leak blood or other fluids, causing scarring and damage to the macula.
AMD has three stages, partially defined by the size and number of drusen beneath the retina. People in early-stage AMD have medium-sized drusen and usually no vision loss. People with intermediate AMD have large drusen, pigment changes in the retina, or both, and most of those affected don't experience any vision loss. People with late AMD have drusen and vision loss, and can develop either dry or wet AMD, according to the NEI.
Diagnosis & tests
AMD may be suspected in people over 60 who experience recent changes in the center of their field of vision.
Several eye tests can help confirm the diagnosis, including:
Visual acuity test: An eye chart is used to measure how well a person can see at different distances.
Dilated eye exam: The pupils are dilated with eye drops so that the optic nerve and retina, located in the back of the eye, can be examined for signs of AMD, according to the Mayo Clinic. A special magnifying lens is used to perform this eye exam, during which an eye doctor is looking for fluid or blood or a mottled appearance. This indicates the presence of drusen under the retina.
Amsler grid: People are asked to look at this grid, which resembles a checkerboard with a black dot in the center. This grid can test for defects in a person's central vision If straight lines in the grid appear wavy or some lines appear to be missing, AMD is more likely.
Angiogram: During this test, a special camera can take pictures of the retina after a colored dye has been injected into a vein in the arm. This dye then travels to the blood vessels in the eye and highlights them. AMD may be present if the images show leaking blood vessels or retinal changes.
Tomography: This painless imaging test uses beams of light to identify whether retinal thinning, thickening or swelling associated with AMD is present, according to the Mayo Clinic.
Treatments & medication
There is currently no treatment for the dry form of AMD, but some people who have a lot of drusen may benefit from taking certain nutritional supplements. Taking a daily high-dose combination of antioxidant vitamins and minerals may slow the progression of dry AMD from the intermediate stage to the advanced stage by as much as 25 percent, according to a large study conducted by the NEI. The formulation includes:
- 500 milligrams (mg) of vitamin C
- 400 International Units (IU) of vitamin E
- 10 mg of lutein
- 2 mg of zeaxanthin
- 80 mg of zinc (as zinc oxide)
- 2 mg of copper (as cupric oxide)
Wet AMD has three main treatments, not all of which are appropriate for every person. They include:
- Injections into the affected eye with a drug that blocks a growth factor stimulating abnormal blood vessel development in the retina
- Laser surgery, uses a high-energy laser beam to seal leaky blood vessels behind the retina
- Photodynamic therapy, which includes the injection of a light-activated drug into the bloodstream. After the injection, a light is shined into the eye for 90 seconds, causing the drug to destroy new blood vessel growth, according to the NEI.
Several lifestyle changes can help AMD patients cope better with resulting vision loss, according to the Mayo Clinic. These include using magnifying lenses and glasses; adjusting computer font size and brightness level; using adaptive appliances such as clocks and telephones with extra-large numbers; trying large-print books, tablet computers and audio books; and brightening room light levels to make reading and other activities easier.
Additional reporting by staff writer Tanya Lewis and contributor Maureen Salamon