What is Macular Degeneration?
Age-related Macular degeneration (AMD) is a disease associated with aging that gradually destroys sharp, central vision. The disease attacks the macula, the central area of the retina that allows a person to see fine detail. Individuals can lose all but the outermost peripheral vision, leaving dim images or black holes at the center of vision. Central vision is needed is needed for seeing objects clearly and for common daily tasks such as reading, driving, identifying faces and watching television. AMD is a leading cause of vision loss and legal blindness in adults over 60 in the United States.
Two Types of Macular Degeneration
Macular degeneration is diagnosed as either dry or wet. Dry AMD is more common than wet AMD, with about 90% of people having the dry type and 10% of people having the wet type. However, even though the wet type is less common, 90% of severe vision loss comes from the wet type and only 10% from the dry type.
Dry AMD occurs when the light-sensitive cells in the macula slowly break down, gradually blurring central vision in the affected eye. It is diagnosed when yellow deposits known as drusen accumulate in the macula. Dry AMD causes gradual central vision loss, but the loss usually is not as severe as can be found with the wet type.
Wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula. These new blood vessels tend to be very fragile and often leak blood and fluid. This blood and fluid raises the macula from its normal place at the back of the eye, causing scarring and permanent damage to light-sensitive retinal cells, which creates blind or blurry spots in the central vision.
Cause of AMD
The cause of AMD is not complemtely known. However, the greatest risk factor is age. The risk of having AMD increases with age, from 10% at age 50 to about 30% at age 75. Other factors that increase the risk of developing AMD include family history of AMD, smoking, diet, weight and race. Caucasians are much more likely to lose vision from AMD than other races (*NIH). Lifestyle practices like not smoking, eating a healthy diet high in green leafy vegetables and fish, exercising and maintaining normal weight and blood pressure may play a role in reducing the risk of developing AMD.
Especially with the dry form, symptoms may develop gradually. Also if only one eye is affected, a person may not notice changes in vision until the disease gets moderately worse because the unaffected eye helps to compensate for changes in vision. Having an annual eye exam is very important for detecting AMD and other ocular disorders early in their progression
Symptoms of AMD may include blurred vision, a dark area or “blind spot”, or a distorted appearance of straight lines or other objects. It is important for people with AMD to monitor their vision closely and to call their eye doctor if there is a change in vision. One way to monitor vision or detect a problem is with an Amsler grid. The Amsler grid, which looks similar to a section of graph paper, is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina. The Amsler grid is a very sensitive test that can reveal clinical changes before other visual symptoms develop. With new and reliable treatments for wet AMD, this tool is important for the early detection of wet AMD..
The National Eye Institute’s Age-Related Eye Disease Study (AREDS) found that taking a specific high-dose formulation of antioxidants and zinc can reduce the risk of progression of dry AMD in some patients. The AREDS formulation is not a cure for AMD. It will not restore vision already lost from the disease. However, it may delay the onset of advanced AMD. It may also help people who are at high risk for developing advanced AMD keep their vision.
Wet AMD can be treated with laser therapy, photodynamic therapy, and injections into the eye. Some patients receive one of these treatments and some patients receive a combination of these treatments. None of these treatments is a cure for wet AMD, but they may halt the progression of the disease and in some cases allow for some gain in visual acuity.
This procedure uses a high energy beam of light to seal or destroy the abnormal blood vessels to prevent leaking and further loss of vision. However, laser treatment may also destroy some surrounding healthy tissue and some vision. Therefore, only a small percentage of people with wet AMD are treated with laser surgery- mainly those whose leaky blood vessels have developed away from the central part of the macula. The risk of new blood vessels developing after laser treatment is high and repeated treatments may be necessary.
This procedure uses a combination of light and drug therapy to destroy leaking blood vessels. First a drug called Verteporfin is injected into a patients arm. It travels throughout the body, including to the eye, where it “sticks” to the surface of new leaky blood vessels. Next, a light is shone into the eye for about 90 seconds. The light activates the drug which destroys the new blood vessels, leading to a slower rate of visual decline. Unlike laser surgery, the drug does not destroy surrounding healthy tissue. This therapy slows the rate of vision loss, but does not stop vision loss altogether or restore vision in eyes already damaged by AMD. Treatment results are often temporary and may need to be repeated.
Anti-VEGF Therapy (Intravitreal Injections)
The treatment of AMD has evolved in the last 5 or so years from limiting the degree of vision loss to maintaining and even improving existing vision in some cases. This is due in no small part to Anti-VEGF (Vascular Endothelial Growth Factor) therapy. Anti-VEGF therapy works by blocking the action of VEGF, the molecule that promotes the growth of abnormal blood vessels under the retina. These drugs are injected directly inside the eye to provide maximum concentration in the area where they are needed. The eye is numbed before each injection. There may be slight discomfort and soreness on the day of the injection, but not pain. Multiple injections will be given as often as monthly, with the goal of achieving up to 3 to 6 months between injections. These drugs maintain vision in up to 90% of all patients treated. Vision may improve in up to 1/3 of treated patients.