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 central 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.
Age-related macular degeneration, as its name implies, affects older individuals. As many as 10% of individuals over 65 and 35% of individuals over 75 will show some signs of this condition. It almost always affects both eyes to some degree, and usually starts with the dry form. The wet form affects approximately 10% of patients with macular degeneration. The most common uncontrollable risk factors for age-related macular degeneration include advanced age and genetic tendency for the disease. However, there are some controllable risk factors that patients are encouraged to actively address: cigarette smoking, nutritional deficiency, and cardiovascular risks such as hypertension.
Clinical Appearance & Symptoms
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 (vision <20/200) 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.
When macular degeneration is identified, your retinal specialist may perform additional testing to further evaluate the condition. The purpose is usually to identify areas of choroidal neovascularization so that potential treatment may be planned or followed. Fluorescein angiography may be employed in the diagnosis of macular degeneration. In this procedure, a dye is injected into an arm vein and travels through the circulatory system to the eye. The dye acts as a tracer and is photographed as it passes through the ocular circulation. Sites of leakage can be identified that correspond to areas of choroidal neovascularization in wet macular degeneration. Areas of drusen and RPE atrophy can be identified in dry macular degeneration. Optical coherence tomography (OCT) is commonly used to obtain a high-resolution image of the retina and any associated thickening from fluid leakage due to choroidal neovascularization. It can sometimes also show the location of the abnormal blood vessels. This technique is very valuable in quantifying the degree of fluid and monitoring response to potential treatment.
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 multi-vitamins. 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; please see the section of this website on prevention for further information on this formulation (the AREDS formula). Your doctor can determine if you would benefit from this product. Retinal intervention is generally aimed at preventing visual loss from choroidal neovascularization. Each therapy is explained in further detail in the Treatments section of this website. There is also a Medications section that reviews current pharmaceuticals used in treating wet age-related macular degeneration.
Antineovascular 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 antineovascular agents and include the drugs Macugen, Avastin, and Lucentis. 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. Retreatment is typically required at 4 to 6 week intervals, depending on the drug used.
Photodynamic Therapy: This treatment involves a combination of drug and laser. A light sensitive drug (photosensitizer) is injected into an arm vein and travels to the retina through the circulation. After 15 minutes, the drug is activated with a low-energy laser targeted at the abnormal growing blood vessels (choroidal neovascularization). This therapy has also shown benefit in preventing or slowing visual loss compared to no treatment. As with the antineovascular agents, most patients will not gain significant vision after treatment; retreatment is typically required at 3 month intervals.
Thermal Laser: In certain cases, a thermal (hot) laser is used to burn the abnormal blood vessels and prevent further growth and corresponding visual loss. The above treatments have largely replaced this method, although thermal laser still has a place in the treatment of wet macular degeneration. Your doctor will discuss all reasonable options for your particular case and decide upon the best treatment with you.