Age-Related Macular Degeneration
Age-related macular degeneration is the most common cause of legal blindness in individuals 65 years or older*. This condition affects the macula, the sensitive middle portion of the retina that is responsible for fine vision (reading, driving, recognizing faces) and color perception. The condition is broadly divided into two forms: a “dry” form and a “wet” form.
The dry form involves aging changes in the tissue that nourishes the retina, the retinal pigment epithelium (RPE). This layer of tissue lines the wall of the eye underneath the retina and is supplied by a network of blood vessels known as the choroid. In the wet form of macular degeneration, abnormal blood vessels grow under the retina from the choroid. These new blood vessels (referred to as choroidal neovascularization) tend to leak fluid, blood, fats, and/or proteins from the bloodstream into the space under the retina; this is where the name “wet” comes from.
The dry form of age-related macular degeneration often starts without symptoms. Upon examination of the retina, patients show changes in the layer that nourishes the retina, the RPE. There are frequently “yellowish” deposits in the RPE layer, known as drusen. The RPE may also show dark clumps known as RPE hyperpigmentation. Finally, the RPE may begin to degenerate to a point where patches of RPE begin to disappear; this is referred to as RPE atrophy and is responsible for most cases of visual loss associated with dry macular degeneration. With the dry form, visual loss tends to be very gradual. Patients may note distortion, dark spots, or blind spots in their vision. Many individuals with dry macular degeneration may maintain excellent visual function for many years. However, those with large patches of RPE atrophy in the central macula may become legally blind from the dry form.
Wet macular degeneration tends to be the more serious form of this condition. As explained above, abnormal blood vessels grow from the choroid in a process known as choroidal neovascularization. These blood vessels may grow within the RPE or through the RPE into the space under the retina. The wet form gets its name from the resulting leakage of fluid, blood, fats, and/or proteins from the bloodstream that typically occurs with choroidal neovascularization. With the wet form, patients often note distortion of images in the earlier stages. With time, patients note dark spots or blind spots as the retina begins to deteriorate over the damaged RPE. Normally, it is the RPE that is responsible for nourishing the retina and keeping it healthy; a damaged RPE is unable to effectively perform this function.
In the later stages of wet macular degeneration, the abnormal blood vessels under the retina become scarred. Scar tissue in the central vision can have severe visual consequences; most patients will become legally blind at this stage and will not be able to read or recognize faces with the affected eye(s). On a positive note, patients with macular degeneration almost never become totally blind. The side vision is almost always preserved, as the macula (central vision) is generally the only area of the retina affected.
The most important aspect in the treatment of age-related macular degeneration is prevention. Patients who smoke are encouraged to stop immediately. Cardiovascular risk factors such as hypertension and elevated cholesterol should be controlled as well as possible. Those with nutritional deficits should improve their diets and consider supplementation with multivitamins. A specific higher risk group of patients will benefit from a specialized nutritional supplement with high doses of vitamin A, C, and E, as well as zinc.
Anti Neovascular Agents: Choroidal neovascularization is triggered by chemicals that are released from the retina. New drugs have been developed that block these chemicals and prevent or slow the growth of new blood vessels. These are termed anti neovascular agents and include the drugs Macugen, Avastin (off-label), and Lucentis (experimental). These drugs are injected directly into the eye and have shown benefits in preserving vision compared to no treatment. Unfortunately, many patients will not gain significant vision after treatment and a certain percentage will continue to lose vision despite treatment. Re-treatment is typically required at 4 to 6 week intervals, depending on the drug used.