Age-Related Macular Degeneration
What Is AMD?
Age-related macular degeneration (AMD) is a common condition affecting people age 50 years and older that is associated with central vision loss, which affects one's ability to read, drive, or see someone’s face if it progresses to more advanced stages.
The macula refers to the central portion of the retina. The retina is similar to film inside a camera. The image one sees is focused by the cornea and lens of the eye onto the center of the retina (macula.) Many people with AMD have minimal visual symptoms and may retain good vision indefinitely. A relatively small percentage of people with AMD will lose central vision, which may impair their ability to read and drive a car. There are two major types of AMD, a "dry" (non-neovascular) and a "wet" (neovascular) form.
Dry AMD, affecting about 90 percent of all people with AMD, is characterized by drusen. Drusen are small yellow deposits that are visible to the doctor on clinical examination of the macula and are the hallmark of AMD. Most people with drusen alone do not have significant visual changes or vision loss. A minority of people with dry AMD will advance to central vision loss due to geographic atrophy, which involves the loss of pigmented cells beneath the macula (these pigmented cells normally act to support and nourish the photoreceptor cells). There is currently no treatment or cure for geographic atrophy, though investigative research is ongoing.
Wet AMD affects only about 10 percent of people with AMD, yet accounts for the majority of central vision loss due to AMD. The word "wet" implies leakage and bleeding in the macula due to abnormal blood vessels (choroidal neovascularization) that may develop spontaneously in AMD. If left untreated, these abnormal blood vessels result in permanent scarring of macular tissue and severe central vision loss. While there is still no cure for wet AMD, we currently have a few medications that are very effective in treating this condition.
Causes And Associations
AMD is a complex, degenerative condition that becomes increasingly prevalent with advanced age. It is typically found in people ages 50 years or more, although drusen sometimes can be seen in younger people. Family history is another important association, although simply having a blood relative with AMD does not necessarily mean or guarantee that one will definitely develop AMD. Other risk factors for AMD may be modifiable or controllable, including smoking, poor nutritional intake, and high blood pressure.
Genetics And AMD
In addition to aforementioned associations, genetics play a key role in AMD, with heredity representing over 70% of the risk of developing the disease. Genetic markers have recently been identified that strongly influence the risk of progression to advanced AMD with vision loss. Several of these gene variants promote inflammation by altering activation of the complement cascade, which is an active part of our immune system. Other gene variants affect mitochondrial function and increase oxidative stress in the retina, consistent with both the role of smoking as a risk factor and the benefit of antioxidants in delaying disease progression. Cholesterol metabolizing enzyme variants are also associated with this disease, consistent with the known biochemical composition of drusen.
Early identification of higher risk patients may help prevent vision loss or slow down disease progression. Environmental risk factors can be identified, lifestyle modifications can be made, and nutritional supplementation can be instituted in these situations to further reduce risk of disease progression. Frequent monitoring of these individuals may result in early detection of wet AMD, leading to better visual outcomes through earlier treatment.
Symptoms Of AMD
Many people with mild dry AMD have little to no visual symptoms. Some people, however, will require more light to read, have difficulty adjusting between dark and light conditions, or notice mild blurring of vision. Occasionally, significant loss of central vision can occur. Vision loss associated with dry AMD is usually gradual or slow. Because AMD affects the macula, the symptoms are typically related to central vision tasks such as reading or driving. Peripheral vision is typically not affected.
Those with wet AMD often have more rapidly progressive loss of central vision, typically over days to weeks. Visual distortion is a common symptom of this stage. Occasionally, however, people may not be aware of these visual changes because their other eye sees well. Therefore, it is important to test vision in each eye separately by covering one eye at a time when checking vision.
An Amsler grid is a self-monitoring tool that allows people to check their vision one eye at a time to monitor for blurring or distortion that may signify the conversion from dry to wet AMD. People with AMD progression may notice changes on the Amsler grid, and if this occurs, they should contact their ophthalmologist promptly.
The Amsler Grid Chart should be used to check the central part of your visual field, the area that can be damaged by Macular Degeneration.
Instructions for Use:
- View the chart (with your reading glasses on) at normal reading distance.
- Completely cover one eye and look at the central dot on the chart.
- Notice if there are any areas within the grid that appear gray (or black), or if there are any areas where the straight lines appear bent, crooked, or missing.
- Check the chart regularly (daily or weekly).
- Call your doctor if new changes occur.