Published: Dec. 13, 2007
Updated: Oct. 5, 2011
The eye is essentially a camera. The role of the eye is to focus light and images from the outside world onto the retina. This is analogous to the role of a camera, which is to focus light and images onto the film. In the eye, the cornea and lens are responsible for focusing light to a pinpoint focus on the retina.
The retina is the part of the eye that is like the film of a camera. Important vision cells in the retina, notably the rods and cones, convert the focused light into an electrical signal, which then travels to the brain through the optic nerve. In the brain that electrical signal is experienced as vision. There are two parts of the retina: the macular retina (responsible for straight-ahead central vision) and the peripheral retina (responsible for side vision).
The macula is the part of the retina responsible for straight-ahead central vision. The macula is used for reading, recognizing faces, and watching television. Any disease that affects the macula, such as age-related macular degeneration, will cause a change and impairment in the central vision.
Age-related macular degeneration (AMD) is the leading cause of central vision loss in the Western world in persons over the age of 55. It is an age-associated degenerative disorder of the macula, the part of the retina responsible for straight-ahead, central vision. As some people age, the macula weakens and its cells begin to break down. This may result in the loss of central vision.
Macular degeneration currently affects approximately 12 million people in the United States. Over the next 20 years, as our population ages, the number of people with AMD is expected to more than double.
There are a number of reasons why people may develop AMD, but age appears to be the main risk factor. In fact, the chance of developing AMD increases with each passing decade after age 50, with 30 percent of people over age 70 exhibiting some sign of the disease.
There are genetic and environmental risk factors as well. Since pigment in the eyes appears to be protective, Caucasians, particularly women, appear to be at a greater risk. Smoking, family history, and sunlight exposure over the course of a lifetime also play a role.
Dry AMD is the most common form of macular degeneration, affecting 90 percent of people with the disease. In the dry form, aging changes called "drusen" become deposited underneath the macula. The changes that AMD patients develop as they age don't necessarily affect quality of life. In fact the vast majority of patients with drusen have no visual changes. However in some AMD patients, drusen can cause the macula to thin, resulting in a gradual decrease in central vision. This late stage of the dry type is called geographic atrophy. If the drusen cause substantial weakening of important layers of the macula, they can set the stage for the "wet" form of AMD.
Wet AMD develops when abnormal blood vessels start to grow through important layers of the macula that have been weakened by the dry form of AMD. This abnormal growth of blood vessels, called choroidal neovascularization (CNV), can cause bleeding, leakage of fluid, and scar tissue formation in highly sensitive parts of the macula. When this happens, loss of central vision can be rapid and severe.
Although only one in 10 patients with AMD will convert from the dry to the wet form, the wet form accounts for 90 percent of the vision loss associated with AMD.
The average chance of converting from the dry to the wet form of AMD is about 2 percent per year. If you have already developed wet AMD in one eye, the chance of developing wet AMD in the other eye can range from 10-75 percent over the next five years depending on certain findings in the retina.
The vast majority of patients with dry AMD will not notice any change in their central vision. However, patients with advanced dry AMD may notice a gradual decrease in their central vision over many months or years. This decline in vision is often accompanied by blank spots that slowly develop in and around the central vision. The most common symptom of wet AMD is the sudden onset of blurred or distorted central vision that may occur over several days or weeks.
Because AMD is a relatively silent disease until advanced stages develop, the only way to know if you have it is to visit your eye care specialist for a dilated eye examination. By dilating the eyes, your doctor can look at the macula for signs of AMD. In some circumstances, your doctor may recommend special photographs to see if there are signs of the wet form of AMD.
It is recommended that all patients over the age of 55 have a dilated eye examination on an annual basis to look for signs of AMD. Now that treatments are available for most patients with either the dry or the wet form of AMD, it is important that AMD be diagnosed as early as possible so that appropriate treatments can be started promptly.
If you have dry macular degeneration and you suddenly notice new distortion or a new blank spot in your vision, you should notify your eye care professional immediately. These symptoms may suggest the development of wet AMD.
You can monitor your vision by regularly covering one eye and looking at a straight object (e.g. a door frame) and asking yourself if it appears straight. Alternatively, you may use an Amsler grid to monitor your vision.
Although AMD can significantly challenge a person's central vision, it is important for patients with AMD to understand that this disease only affects the center of the vision and will not cause them to go "completely blind." In fact, in 99 percent of the cases, the side vision remains unaffected, allowing for independent living and getting around. Furthermore, vision rehabilitation specialists can often assist AMD patients who have sup-optimal central vision to learn how to use their side vision more effectively. This can result in enhanced quality of life for many patients with AMD.
The various treatment options for AMD depend on the type and stage of AMD that is present.
At this time, the only treatment for dry AMD is high-dose antioxidant vitamin therapy.
Treatment options for the wet form of AMD include:
The Age-Related Eye Disease Study (AREDS) showed that taking high-dose antioxidant vitamins and zinc significantly slowed the rate of progression of vision loss in patients who had more advanced forms of AMD.
AREDS II is an ongoing study to understand the role of certain other vitamins.
The following vitamin combination was proven effective in the Age-Related Eye Disease Study (AREDS):
Vitamin therapy for AMD will help slow the progression of AMD. Vitamins are not a cure for AMD and will not give back any vision that has already been lost.
Only those patients with intermediate to advanced forms of AMD should be taking the high-dose multivitamin formula. Ask your doctor if you should be taking this vitamin supplement.
Age-Related Eye Disease Study (AREDS) researchers say it is unclear if the possible increased risk associated with very high doses -- 500 IU to 2000 IU -- of vitamin E applies to people taking 400 IU. An increased risk of mortality was not found among those taking about 400 IU of vitamin E.
The National Institutes of Health Office of Dietary Supplements has a fact sheet on vitamin E that summarizes the research on vitamin E and different chronic diseases.
We do not believe that people who do not have AMD should supplement with the high-dose vitamin formula in the hopes of preventing AMD from developing.
The Age-Related Eye Disease Study (AREDS) vitamin formula is available over the counter without a prescription in most pharmacies, retailers, and grocery stores. Common brand names include Ocuvite Preservision and Alcon ICaps® AREDS.
Lutein and zeaxanthin are natural pigments that are normally found in the human macula. They are thought to play a protective role in the macula. The effects of lutein and zeaxanthin in AMD are being studied in the AREDS II trial.
Most patients in the Age-Related Eye Disease Study (AREDS) continued to take their regular multivitamins in addition to the AREDS formula. We recommend that you check with your family medical doctor or internist to be sure that it is okay for you to continue to take all of these vitamins.
In hot laser therapy, a laser is used to cauterize the abnormal blood vessels growing underneath the retina in the wet form of AMD. Unfortunately, hot laser therapy also burns through the overlying retina in order to cauterize the blood vessels beneath. In doing so, hot laser therapy creates a permanent blank spot in a person's vision.
Hot laser therapy continues to be used in many patients when the abnormal blood vessels are not growing directly underneath the center of the macula (center of the vision).
The greatest reason for hot laser treatment failure is that the blood vessels can grow back up to 50 percent of the time. If you undergo hot laser treatment, your doctor will be following you closely to look for any signs of the blood vessels growing back.
Cold laser therapy was developed for blood vessels that lie directly underneath the center of the vision. In cold laser treatment, a light-sensitive drug is injected into your arm vein and travels with your circulation to the abnormal blood vessels underneath the retina. A cold laser is then directed at this area of your macula. This laser, unlike the hot laser, does not burn your overlying retina. When the cold laser light hits the light-sensitive drug in the abnormal blood vessels, it turns the drug "on." Once the drug is turned on, it causes a chemical reaction to occur, which leads to a blood clot forming in the blood vessels, closing them down.
Unfortunately, in cold laser therapy, the blood vessels have a tendency to "open up again." If this happens, a repeat cold laser therapy may be recommended again until the blood vessels stay closed. Your doctor will determine at regular intervals whether this therapy needs to be repeated. The goal of cold laser therapy is not to make the vision better, but to decrease the rate of the vision getting worse.
With the advent of newer anti-angiogenesis therapies (i.e. Macugen, Lucentis, and Avestin), this method of treatment is used less frequently. However, your doctor may use this for certain types of new vessel growth or in certain locations. Also, your doctor may recommend a combination of treatment modalities.
Macugen was the first anti-vascular endothelial growth factor (VEGF) therapy that used to target the underlying leaky blood vessels in the "wet" form of macular degeneration. This drug works by blocking vascular endothelial growth factor (VEGF165) protein that promotes blood vessel growth. Macugen is administered by intravitreal injection every six weeks for the course of a year. While Macugen is used less frequently than Lucentis and Avastin, it may still be used in certain health settings.
Lucentis is another drug that blocks vascular endothelial growth factor (VEGF). It also works to decrease blood vessel growth and leakage. Lucentis offers hope of improvement in vision for some patients and helps to stabilize vision for most patients. In the early treatment stages, Lucentis is repeated every four weeks. For subsequent treatments, reinjections may be performed based on the activity of the blood vessels or on a scheduled maintenance therapy. Optimal timing of re-treatments is still under investigation.
Before Lucentis was available, retina specialists started to use a similar drug called Avastin, which was available for cancer treatment. The results that retinal specialists have seen with Avastin appear to be similar to Lucentis. While both drugs are made by the same company, there is a large difference in cost: Lucentis is very expensive while Avastin is relatively inexpensive.
In macular translocation surgery, which was developed at Duke Eye Center, a surgical procedure is performed to rotate the macula away from the abnormal blood vessels and to a healthier part of the back of the eye. This surgery is useful for patients who have:
Cynthia Toth, MD, is a world leader in this surgical procedure and continues to perform groundbreaking discoveries in this area. Your doctor will tell you if macular translocation is an option for you.
Depending on the type of new blood vessels and the location, your doctor may talk to you about combining treatments to optimize treatment effect. Steroids work by decreasing inflammation and are sometimes used with combination therapy.
Although several treatments have been developed for wet AMD over the years, most of them remain sub-optimal for either very late stages of wet AMD or certain types of wet AMD that can remain stable.
In such circumstances your doctor may recommend observation rather than a treatment that will either have no benefit to you or potentially make the problem worse.
If your doctor has recommended observation, he or she will follow you closely to watch for any change in your blood vessels. Should your blood vessel characteristics change, your doctor may recommend a different course of therapy.
At the Duke Center for Macular Diseases, retina experts will be focusing on the treatment of your AMD. You will continue to see your general ophthalmologist or other eye care provider for all other routine eye care.
The treatment options for dry and wet AMD are still sub-optimal and aim to stabilize vision. Low vision services are often helpful for patients who have or may develop sub-optimal levels of vision secondary to AMD. A low vision specialist can train patients to use the vision they do have more effectively. Such an evaluation is custom-tailored to the specific needs of the patient.
See information about vision rehabilitation specialist Diane Whitaker, OD.
Learn more about macular degeneration: