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Macular degeneration, often called AMD or ARMD (age-related macular degeneration) occurs with degeneration of the macula, which is the part of the retina responsible for the sharp, central vision that we primarily use when reading or driving. Because the macula primarily is affected in AMD, central vision loss may occur
Wet and Dry Forms of Macular Degeneration
Macular degeneration is diagnosed as either dry (non-neovascular) or wet (neovascular). Neovascular refers to growth of new blood vessels in an area, such as the macula, where they are not supposed to be. The wet form of the disease usually leads to more serious vision loss.
The dry form is more common than the wet, with about 85-90 percent of AMD patients diagnosed with dry AMD.
Dry Macular Degeneration (non-neovascular). Dry AMD is an early stage of the disease and may result from the aging and thinning of macular tissues, depositing of pigment in the macula or a combination of the two processes.
Dry macular degeneration is diagnosed when yellowish spots known as drusen begin to accumulate from deposits or debris from deteriorating tissue mostly around the macula. Gradual central vision loss may occur with dry macular degeneration but is not nearly as severe as wet AMD symptoms.
No FDA-approved treatments are available for dry macular degeneration. A major National Eye Institute study (AREDS) has produced strong evidence that certain nutrients such as beta carotene (vitamin A) and vitamins C and E may help prevent or slow progression of dry macular degeneration.
Wet Macular Degeneration (neovascular). In about 10 percent of cases, dry AMD progresses to the more advanced and damaging form of the eye disease. With wet macular degeneration, new blood vessels grow (neovascularization) beneath the retina and leak blood and fluid. This leakage causes permanent damage to light-sensitive retinal cells, which die off and create blind spots in central vision. Neovascularization is the body’s misguided way of attempting to create a new network of blood vessels to supply more nutrients and oxygen to the eye’s retina. Instead, the process creates scarring, leading to sometimes severe central vision loss.
Wet macular degeneration falls into two categories:
Occult. New blood vessel growth beneath the retina is not as pronounced, and leakage is less evident in the occult CNV form of wet macular degeneration, which typically produces less severe vision loss.
Classic. When blood vessel growth and scarring have very clear, delineated outlines observed beneath the retina, this type of wet AMD is known as classic choroidal neovascularization (CNV), usually producing more severe vision loss.
Macular degeneration usually produces a slow, or rarely, sudden painless loss of vision. Early signs of vision loss from AMD include shadowy areas in your central vision or unusually fuzzy or distorted vision.
An Amsler grid consists of straight lines, with a reference dot in the center. Someone with macular degeneration may see some of the lines as wavy or blurred, with some dark areas at the center. This test is one way to check if you are having macular degeneration. Click here to try an Amsler grid test yourself.
If your eye doctor detects some defect in your central vision, such as distortion or blurriness, he or she may order a fluorescein angiography to examine the retinal blood vessels surrounding the macula.
Many forms of macular degeneration are linked to aging and related deterioration of eye tissue crucial for good vision. Duke University and other researchers have noted a strong association between development of the eye disease and presence of a variant of a gene known as complement factor H (CFH). This gene deficiency is associated with almost half of all potentially blinding cases of macular degeneration.
Columbia University Medical Center and other investigators reported in March 2006 that variants of another gene, complement factor B, may be involved in development of AMD. Specific variants of one or both of these genes, which play a role in the body’s immune responses, have been found in 74 percent of AMD patients who were studied.
Deteriorating, oxygen-starved cells within the retina likely help trigger neovascularization and accompanying damage in wet AMD. Neovascularization is activated by a protein called vascular endothelial growth factor (VEGF), targeted in wet macular degeneration treatments by anti-VEGF drugs.
Besides affecting older populations, AMD occurs in whites and females in particular. The disease also can result as a side effect of some drugs, and it seems to run in families.
New evidence strongly suggests that smoking is high on the list of risk factors for macular degeneration. Other risk factors for AMD include high blood pressure, lighter eye color and obesity. Some researchers believe that over-exposure to sunlight also may be a contributing factor in development of macular degeneration, but this theory has not been proven conclusively. High levels of dietary fat also may be a risk factor for developing AMD.
The American Academy of Ophthalmology notes that findings regarding AMD and risk factors have been contradictory, depending on the study. The only risk factors consistently found in studies to be associated with the eye disease are aging and smoking.
Commonly named risk factors for developing macular degeneration include:
Aging. Significant vision loss accompanying more advanced forms of AMD increases from fewer than 1 percent among people in their 60s to more than 15 percent among people in their 90s, according to the Canadian Medical Association Journal (Feb. 17, 2004 edition).
Obesity and Inactivity. Overweight patients with macular degeneration had more than double the risk of developing advanced forms of macular degeneration compared with people of normal body weight, according to one study reported in Archives of Ophthalmology (June 2003). In the same study, those who performed vigorous activity at least three times weekly reduced their risk of developing advanced AMD, compared with inactive patients.
Heredity. As stated above, recent studies have found that specific variants of two different genes are present in most people who have macular degeneration. Studies of fraternal and identical twins may also demonstrate that heredity is a factor in who develops AMD and how severe it becomes.
High Blood Pressure (Hypertension). Investigative Ophthalmology and Vision Science reported a study in Rotterdam, The Netherlands demonstrating that high blood pressure may be associated with development of macular degeneration (September 2003).
Smoking. Smoking is a major risk factor found in one British study to be directly associated with about 25 percent of AMD cases causing severe vision loss. The British Journal of Ophthalmology in early 2006 also reported study findings showing that people living with a smoker double their risk of developing AMD.
Lighter Eye Color. Because macular degeneration long has been thought to occur more often in lighter skinned populations, particularly in people with light eye color, some researchers theorized that the extra pigment found in darker eyes was a protective factor against development of the eye disease during sun exposure. But no conclusive evidence as yet has linked excessive sun exposure to development of AMD.
Drug Side Effects. Some cases of macular degeneration can be induced from side effects of toxic drugs.
There is as yet no outright cure for macular degeneration, but some treatments may delay its progression or even improve vision such as nutritional intervention.
Treatments for macular degeneration depend on whether the disease is in its early-stage, dry form or in the more advanced, wet form that can lead to serious vision loss.
For wet AMD, treatments aimed at stopping abnormal blood vessel growth include FDA-approved drugs of Lucentis, Macugen and Visudyne used with Photodynamic Therapy or PDT. Lucentis has been shown to improve vision in a significant number of people with macular degeneration.
Although much progress has been made recently in macular degeneration treatment research, complete recovery of vision lost to AMD is unlikely. Your eye doctor may ask you to check your vision regularly with the Amsler grid described above. Viewing the Amsler grid separately with each eye helps you monitor your vision loss. The Amsler grid is a very sensitive test that typically reveals clinical findings before the doctor can actually see physical findings.
For those who have suffered vision loss, many low vision devices are available to help with vision tasks by using magnifying lenses and bright lights. Some low vision aids shift images to the periphery for clearer vision.
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