Age-Related Macular Degeneration
The National Eye Institute has identified age-related macular degeneration (AMD) as a major problem with increasing prevalence as the average lifespan increases. Scheie Eye Institute is a world leader in basic and clinical research on AMD. Recent advances at Scheie have included evidence of association between inflammation and iron overload with AMD. Ophthalmologists on Scheie’s Retina Service perform basic and clinical research and take care of patients in the practice.
What is Age-Related Macular Degeneration?
Macular degeneration is the leading cause of severe vision loss in people over age 50 in the western world. This condition is also referred to as age-related macular degeneration or “AMD.” In macular degeneration, vision loss occurs when the cells in the light sensitive region of the eye, known as the retina, start to deteriorate or break down. The most severely affected cells are those within a special region of the retina known as the macula, which is responsible for fine detail vision. The type of vision loss - central detail vision - affects reading, driving, sewing, watching TV, and any other task that requires focusing on small objects.
Although macular degeneration reduces central vision, side vision remains clear. Macular degeneration alone does not result in total blindness and most people continue to have some useful vision and are able to take care of themselves.
Dry Macular Degeneration
There are two main types of macular degeneration: “dry” and “wet.” Dry is the most common type of macular degeneration and vision loss is usually gradual. Some patients with dry AMD maintain good reading vision for their entire lives. In its early stages, changes in vision may be hard to notice. One may notice that straight lines appear wavy, or that there are blank spots in the center of vision. Colors may look dim. There is no way to restore vision lost from dry AMD. However, dry macular degeneration must be monitored because it can turn into wet macular degeneration.
Wet Macular Degeneration
Wet macular degeneration results when abnormal blood vessels form underneath the retina and leak blood or fluid thus causing that portion of the retina to bulge. This bulging of the retina distorts vision. An eye with wet macular degeneration will usually lose its ability to see fine detail, although prompt treatment may slow, minimize, and sometimes reverse vision loss. While only 10% of people with macular degeneration have the wet kind, it accounts for about 90% of the cases that lead to severe vision loss.
Causes of Macular Degeneration
Many older people develop macular degeneration as a part of the natural aging process. In addition to age, there are several characteristics that people with macular degeneration have in common. These include family history, smoking, or having blue or light colored eyes. Although seen as common factors in people with macular degeneration, it is not specifically known to what degree these characteristics actually increase one’s risk for developing macular degeneration.
The development of drusen may also be a precursor to the development of macular degeneration.
What are Drusen?
Drusen are deposits that lie beneath the retina. Drusen can be thought of as backed up waste products from various layers of the retina. Drusen can be a marker for macular degeneration (especially in the over 50 age group) because there appears to be an increased risk for macular degeneration as the number of drusen increases. Fat also accumulates in Bruch’s membrane with age. This may also contribute to drusen formation.
Drusen occurs in two forms:
- Hard, small – these do not increase with age and do not pre-dispose to macular degeneration
- Soft, large – these are associated with age, may enlarge, and may predispose to macular degeneration.
Persons with large, soft drusen may also be at risk for subretinal bleeding.
Prognosis and Treatment for Drusen
The appearance of drusen is a common finding in older patients and 7does not necessarily indicate the onset of vision loss. There is no clinically effective way to treat drusen. However, several clinical trials are underway to evaluate various methods, including laser treatments, and their effects on drusen reduction, and on the progression of macular degeneration.
It is very important to be followed closely by an ophthalmologist if drusen are present. On ophthalmologist can monitor subtle changes in the retina, and manage any complications that may arise. Persons with drusen should also perform a self-test called an Amsler grid, or a routine basis to monitor for the presence of visual distortions.
Prevention of Macular Degeneration
The cause of macular degeneration is not clearly understood and thus, most methods of prevention are unproven. The AREDS study demonstrated convincingly that a mixture of antioxidant vitamins could significantly reduce the risk of vision loss in patients with a certain number of large or intermediate size drusen. These vitamins a not entirely without risk, and should only be taken under the guidance of an ophthalmologist.
Demographic studies examining people with macular degeneration and their common characteristics suggest that there may be ways to minimize one’s risk for developing macular degeneration. These include cessation of smoking, wearing sunglasses, and eating a diet rich in fruits, vegetables, and fish. Although studies examining these interventions have produced conflicting results with regard to preventing or minimizing macular degeneration, studies showing the general health value of stopping smoking and eating a diet rich in antioxidants are well supported.
Detection of Macular Degeneration
In the early stages of macular degeneration, vision may seem blurred or somewhat distorted; or a blank spot may be seen in one’s vision. Straight edges may seem bent or wavy. One may notice that each eye perceives the size or color of an object differently. Many people may not even notice early changes in vision because only one eye is affected while the other continues to see well. It is very important that any distortion of vision be promptly reported to an ophthalmologist for further evaluation.
Treatment of Macular Degeneration
Despite ongoing research, there is no cure or medical treatment for the “dry” form of macular degeneration, other than prevention with antioxidant vitamins. However, low vision rehabilitation is very useful in helping people use their remaining vision in order to perform activities of daily living and maintain as high a level of independence as possible.
Certain types of “wet” macular degeneration can be treated with laser therapy. Traditional laser therapy uses a highly focused light to dry up leaking blood vessels or preventing them from continuing to grow. The area treated with the laser becomes a permanent blind spot. However, the vision loss is usually less severe than if laser therapy was not done. Laser treatment does not permanently stop the formation of new blood vessels. Therefore, repeat treatments are usually needed.
Photodynamic Therapy (PDT)
Another type of laser treatment, PDT, uses the medication Visudyne that causes light sensitivity, and a low intensity laser. PDT may slow vision loss and in some cases, improve vision. Research suggests this treatment may be effective for 10 – 15% of people with the “wet” form of macular degeneration. Unlike traditional laser therapy, PDT does not cause a blind spot on the retina.
PDT treatment is considered effective for AMD when vision loss results from blood vessels leaking under the center of the retina. A test known as fluorescein angiography can determine whether a particular person with AMD can be treated with PDT. About 10% to 15% of people with wet macular degeneration may benefit.
Lucentis, Avastin, and Macugen
The growth of blood vessels under the retina in wet macular degeneration is fueled by a growth factor called vascular endothelial growth factor (VEGF). Several drugs that can be injected into the eye through a tiny needle have been developed to target VEGF and prevent it from stimulating blood vessel growth. In large clinical trials, Macugen was shown in a large clinical trial to reduce the risk of vision loss and Lucentis was shown in a large clinical trial, on average, to improve vision. Avastin, which is very similar to Lucentis, has been used off-label on many patients and improved vision in published reports testing small numbers of patients. Patients who receive injections of Avastin, Lucentis, or Macugen often need repeat injections to prevent recurrence of wet AMD. The optimal frequency and number of injections is a subject of intense study.
Low Vision Aids
Vision aids can help with tasks that require detail vision. It is also helpful to see a low vision specialist, a doctor specifically trained in low vision rehabilitation. Aids such as magnifiers, writing guides, large-faced appliances and clocks, and large print books can help people continue to read and take care of themselves.