Age-related Macular Degeneration (AMD)
Age-related Macular Degeneration (AMD), the leading cause of legal blindness in people 65 years or older in the United States, affects more than 10 million Americans according to Prevent Blindness America. People with AMD may have difficulty with daily tasks that require fine vision such as reading, driving, recognizing faces, and dialing a telephone. However, AMD does not typically damage the side vision, which is what one uses to get around without bumping into furniture or other objects.
What is Macular Degeneration?
The retina is a layer within the eye made up of nerve cells that perceive light which is then transmitted to the brain so that we have vision. Thus, the retina acts very much like the film in a camera. Vision is distorted or decreased with significant AMD.
The retina has blood vessels that run within it just like the pattern in a wallpaper, but it also depends on support for proper nourishment from an underlying layer of blood vessels called the choroid. In between the choroid and the retina is a barrier filter called Bruch’s membrane that prevents unwanted fluid from accumulating under the retina. Although we talk of the macula as the central part of the retina the critical area within the macula is called the fovea. This is only 1/15 of an inch in diameter, about the size of a pinhead. Thus, our central vision which allows us to read and see fine detail depends on the health of this small, but very highly specialized area.
What Causes Macular Degeneration?
While we do not understand completely how the changes occur, dry macular degeneration is due to atrophy (wasting away of retinal tissue). In the wet form vision loss is usually caused by the growth of abnormal blood vessels that leak fluid and blood under the foveal area of the macula. The dry type of macular degeneration affects 90% of patients and the wet type the remaining 10%. Most macular degenerations start out as the dry type. The rate of visual loss in the dry stage is highly variable and many people maintain reading vision and good distance vision for years. At any time in the course of the disease, however, the condition can convert to the wet type and, at that point, significant visual symptoms usually suddenly occur.
In the wet type of AMD abnormal blood vessels from the choroid grow through cracks in the barrier filter (Bruch’s membrane) like grass through cracks in the sidewalk. They then leak fluid or blood and it is this leakage that initially distorts or decreases the vision. Ultimately, a large scar may form secondary to the leakage and bleeding which has occurred under the retina.
Although there is no way to halt or reverse damage from dry age-related macular degeneration, certain lifestyle and dietary measures can be taken that can help to decrease the risk of disease progression to the more advanced stages.
If you smoke cigarettes, you should try to stop. Smoking increases your risk of disease progression. Studies also suggest that a diet rich in leafy green vegetables may be beneficial. (If you are taking certain types of blood thinners, ask your medical doctor first before making significant dietary changes since they could negate to some degree the affect of some blood thinners.)
Lastly, published results from the Age-Related Eye Disease Study (AREDS) showed that a certain formulation of anti-oxidant vitamins and minerals can reduce the risk of dry age-related macular degeneration progressing to more advanced stages and associated vision loss. The daily dose of vitamins used in the study is listed here:
- 500 mg. vitamin C
- 400 I.U. vitamin E
- 15 mg. of beta carotene
- 80 mg. of zinc oxide
- 2 mg. copper oxide
Please check with your doctor before starting this vitamin/mineral combination. In general, Vitamin E supplementation should not exceed 400 I.U. and smokers should not be on any beta carotene supplementation.
Risk Factors for AMD include:
- Family history of AMD (parents, brothers and sisters with the disease). Patients with a family history may show large drusen (yellow spots under the retina).
- High blood pressure and high cholesterol levels
Eight things You Can Do to Help Preserve Your Vision
- Do not smoke.
- Focus on healthy eating with a diet rich in green leafy vegetables, fruits, and fish once or twice a week.
- Cook with virgin olive oil, and avoid trans fats found in processed baked goods.
- Maintain normal blood pressure and cholesterol levels.
- Watch your weight.
- If you have been diagnosed with intermediate level dry AMD or advanced dry AMD in one eye, take the vitamin and mineral combination of vitamin C, vitamin E, beta-carotene and zinc, as stated earlier, in the form of Ocuvite or ICAPS after checking with your personal physician (once again smokers should not take beta-carotene).
- Screening of those with a family history of AMD and those who smoke should be encouraged so that if large drusen are noted, the appropriate nutritional supplements mentioned earlier can be recommended. Because macular degeneration is more common as one gets older we encourage those in the Medicare population to be screened as well.
A series of studies sponsored by the National Institute of Health have proven that selected patients with wet macular degeneration have a lower risk of severe visual loss if they are treated by laser photocoagulation than if no treatment is instituted. It is estimated that about 10-15% of patients with the wet type of macular degeneration may be candidates for standard laser therapy. While the treatment may successfully eliminate the abnormal vessels, in approximately 50% of patients the abnormal vessels cannot be permanently obliterated.
Photodynamic therapy (PDT) with verteporfin (Visudyne)
PDT utilizes both an injection of a photosensitizing drug called verteporfin (Visudyne) and a non-thermal laser light exposure to treat certain types of choroidal neovascularization. Clinical trials have shown PDT to be effective in slowing down or limiting the amount of vision loss in patients who have choroidal neovascularization located directly under the center of the retina. The treatment does not, however, lead to recovery of vision already lost from the disease process and it may not prevent additional loss in all patients. Currently, steroid solutions injected directly into the eye before or after PDT are being explored to see if they reduce swelling in the retina, thereby enhancing the effect of PDT.
Anti-Blood Vessel Medical Therapy
Many new drugs are being developed that block blood vessel growth factors in the eye which have been shown to be involved in the development of choroidal neovascularization. In wet AMD these drugs may inhibit or slow the growth of the neovascularization and also possibly reduce its leakiness. Recent clinical trials have shown that treatment for wet AMD with centrally located choroidal neovascularization significantly reduced vision loss associated with wet AMD, but only rarely did the treatment result in any vision improvement.