What is AMD?
Age-related macular degeneration, also known as AMD, is a progressive, degenerative condition affecting the macula, or central portion of the retina. The macula, measuring approximately a quarter inch across, is the part of the retina responsible for fine, detailed, central vision. Damage to the macula, as occurs in AMD, can lead to blurring, distortion, or loss of central vision. Peripheral vision is usually maintained.
There are two basic types of AMD. In non-exudative, or “dry” AMD, there is typically slowly progressive damage to and degeneration of the pigmented epithelial cells which support and nourish the retina.
As these cells are injured, waste material and cellular debris is deposited beneath the retina forming drusen, yellow spots which are visible during an eye examination.
The loss of epithelial cells leads to injury to the overlying retina, eventually resulting in loss of vision. This process is usually slow, and good visual function is often maintained for many years after the disease is diagnosed. A normal macula is pictured to the right, and a macula with drusen to the left.
About 10-15 percent of patients with dry AMD will go on to develop exudative, or “wet” disease.In this case, the disturbance in the pigment epithelium and retina leads to the development of abnormal blood vessels beneath the retina, possibly as an attempt to heal the damage.
These vessels are abnormally fragile,however, and often leak and bleed under the retina. This leakage of fluid and blood often causes a sudden change in vision, noted as distortion or warping of straight lines, or even as a blank spot in the center of vision. If untreated, the affected area often heals with a large scar, causing permanent loss of vision.
How common is AMD?
AMD is the leading cause of vision loss in Americans over 50 years of age, with about 15 million people affected and 200,000 new cases diagnosed each year.
What causes AMD?
The exact causes of AMD are not known, though numerous risk factors have been identified. These include:
- Age: As the name implies, the risk of AMD increases significantly with advancing age. The disease affects about 18% of Americans between 70 and 74 years of age, and 45% of those over 85.
- Genetics: Genetics appear to play a significant role, with increased risk of AMD in first degree relatives of affected individuals. Individual genes responsible for the disease are presently being identified.
- Smoking: At least two studies have found that smoking increases risk, possibly twofold.
- High fat diet: A diet high in unsaturated fats may increase the risk of developing wet AMD.
- Ultraviolet light exposure: Though this remains controversial, some studies suggest that long-term exposure to sunlight may increase one’s risk of developing the disease.
How is AMD diagnosed?
During your eye examination, the doctor will carefully study your macula for changes consistent with AMD, including abnormalities of the pigmented epithelial cells, presence of drusen, or leakage of fluid or blood under the retina. If necessary, consultation with a retinal specialist may be arranged for special testing, including fluorescein angiography or ocular coherence tomography (OCT).
In fluorescein angiography, dye, which is injected into a vein in the arm, travels through the circulation until it reaches the blood vessels in the back of the eye. A series of photographs is taken, documenting the patterns produced as the dye moves through the retina and surrounding tissues. This test can often demonstrate changes which cannot be seen by the naked eye. OCT uses a special laser to scan the back of the eye, producing images of the retina and surrounding tissues. Similar to ultrasound, but with much better resolution and detail, OCT can identify abnormal areas of leakage which cannot be seen by examination alone.
Self monitoring for changes in vision is very important in macular degeneration.An Amsler grid is a tool used for this purpose, and is pictured to the right. This grid will help identify distortion of straight lines, often a symptom of wet AMD.
A full sized Amsler grid is available for download from the ‘download forms’ page.
How is AMD treated?
Treatment for AMD depends upon the type of disease present. Dry AMD has no specific medical or surgical treatment. Recommendations include reduction of as many risk factors as possible- stop smoking, control high blood pressure and cholesterol, and avoid excessive unsaturated fats. Recently, the results of a long-term, multi-center clinical trial supported by the National Institutes of Health were published. Known as the Age Related Eye Disease Study (AREDS), this trial found that treatment with a formula consisting of antioxidant vitamins and minerals, including vitamin C, E, A (beta carotene), zinc, and copper, reduced the risk of progression of AMD by about 25%. Based on this finding, this combination of nutrients is often recommended to AMD patients. A number of companies commercially produce vitamin formulas specifically for this purpose. Care must be taken, however, not to take too much of some of these vitamins. Also, beta carotene should not be taken by smokers, as this may increase the risk of lung cancer. Discuss any treatment with your eye doctor and primary care physician before starting.
There are a number of treatment options for wet AMD. Traditional thermal laser therapy involves treating an area of abnormal blood vessel growth with a thermal laser, destroying the vessels and preventing further leakage or bleeding. Thermal laser is effective, however is not currently appropriate for the majority of wet AMD patients due to the location of the blood vessels in the macula. A newer treatment, called photodynamic therapy, or PDT, is available to treat many of these patients. In PDT, a light-activated chemical, which is injected into a vein in the arm, is absorbed by the abnormal blood vessels beneath the retina. A “cold” laser is then focused on the macula, activating the chemical, which then destroys the abnormal blood vessels while avoiding damage to surrounding tissues. While PDT is quite effective, it too is unable to treat all AMD lesions.
A number of medications have become available in recent years for the treatment of wet AMD, including Lucentis®, Avastin®, and Macugen®. Injected into the eye, these medications bind to a molecule known as VEGF (vascular endothelial growth factor), which is responsible for the growth of the abnormal blood vessels in wet AMD. These VEGF-inhibitors have proven quite effective in the treatment of lesions which were untreatable in the past. They may be used in conjunction with PDT or thermal laser treatment, and are quickly becoming the standard therapy in this disease.
Diagnosis and treatment of AMD requires a thorough eye examination. If you are over 50, have a family member with the disease, or suffer any of the symptoms noted above, contact us today for an appointment with one of our physicians.