Macular degeneration, often called AMD or ARMD (age-related macular degeneration), is the leading cause of vision loss and blindness in Americans aged 65 and older. Because older people represent an increasingly larger percentage of the general population, vision loss associated with AMD is a growing problem.
AMD occurs with degeneration of the macula, which is the part of the retina responsible for the sharp, central vision needed to read or drive. Because the macula primarily is affected in AMD, central vision loss may occur.
Archives of Ophthalmology in 2004 estimated that 1.75 million U.S. residents now have significant symptoms associated with age-related macular degeneration, with that number expected to grow to almost 3 million by 2020.
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 primarily in the area of the macula. Gradual central vision loss may occur with dry macular degeneration but is not nearly as severe as symptoms associated with the wet form of AMD.
No FDA-approved treatments are available for the dry form of 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.
The AREDS study indicates that taking high dose formulas of certain nutritional supplements can reduce risk of early stage AMD progression by 25%. Some eye doctors also recommend that dry AMD patients wear sunglasses with UV protection against potentially harmful effects of the sun.
Wet Macular Degeneration (neovascular). In about 10% of cases, dry AMD progresses to a more advanced and damaging form of the eye disease known as wet macular degeneration. With wet AMD, 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, the underlying process causing wet AMD and abnormal blood vessel growth, 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. But the process instead creates scarring, leading to sometimes severe central vision loss.
Wet forms of macular degeneration are further classified into two general types:
Classic. When blood vessel growth and scarring has very clear, delineated outlines observed beneath the retina, this type of wet AMD is known as classic choroidal neovascularization (CNV) usually associated with more severe vision loss.
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.
Macular degeneration usually produces a slow, or rarely, sudden painless loss of vision. Early signs of vision loss associated with AMD can include seeing shadowy areas in your central vision or experiencing unusually fuzzy or distorted vision.
Viewing a chart of black lines arranged in a graph pattern (Amsler grid) is one way to tell if you are having these vision problems.
An eyecare practitioner often detects early signs of macular degeneration before symptoms occur. Usually this is accomplished through a retinal examination. When macular degeneration is suspected, a brief test using an Amsler grid that measures your central vision may be performed. If the eyecare practitioner detects some defect in your central vision, such as distortion or blurriness, he or she may order a fluorescein angiography to specifically examine the retinal blood vessels surrounding the macula.
Information released in March 2006 from Columbia University Medical Center and other investigators also indicates that variants of another gene, known as 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% of AMD patients who were studied.
Ophthalmology Clinics of North America (December 2003) reported that 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 appears to occur in whites and females in particular. The disease also can result as a side effect of some drugs, and it appears 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 having a family member with AMD, 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% among individuals in their 60s to more than 15% among people in their 90s, according to the Feb. 17, 2004 edition of Canadian Medical Association Journal (CMAJ).
Smoking. Smoking is a major risk factor found in one British study to be directly associated with about 25% 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.
Heredity. Recent studies have found that specific variants of two different genes are present in most people who have macular degeneration [See "What Causes Macular Degeneration" above]. 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). In September 2003, 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.
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 the June 2003 issue of Archives of Ophthalmology. 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.
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.
A small study reported in January 2006 in the British Journal of Ophthalmology found no connection between the eye disease and sun exposure. In fact, the same study found no relation at all between lighter eye color, hair color, and AMD. That finding is contradicted by several earlier studies indicating that lighter skin and eyes are associated with a greater prevalence of AMD.
Drug Side Effects. Some cases of macular degeneration can be induced from side effects of toxic drugs such as Aralen (chloroquine, an anti-malarial drug) or phenothiazine. Phenothiazine is a class of anti-psychotic drugs, including brand names of Thorazine (chlorpromazine, which is also used to treat nausea and vomiting, and intractable hiccups), Mellaril (thioridazine), Prolixin (fluphenazine), Trilafon (perphenazine) and Stelazine (trifluoperazine).
Treatments for macular degeneration depend on whether the disease is in its early stage or dry form or more advanced, wet form that can lead to serious vision loss. There are no FDA-approved treatments for dry macular degeneration, although nutritional intervention may be valuable in preventing its progression to the more advanced, wet form.
For wet AMD, treatments aimed at stopping abnormal blood vessel growth include FDA-approved drugs of Macugen and Visudyne used with Photodynamic Therapy or PDT. Some new investigative treatments such as Lucentis and Avastin are showing promise for possibly even reducing vision loss in a significant number of macular degeneration patients.
Phase two of the AREDS study began in late 2005 to evaluate whether similar protective effects against AMD might be associated with other nutrients such as omega-3 fatty acids or "good fats," and lutein and zeaxanthin found in green, leafy vegetables.
The August 2001 issue of Archives of Ophthalmology reported findings that consumption of omega-3 fatty acids, which are particularly prevalent in cold-water fish, also had a protective effect against advanced macular degeneration. Meanwhile, consumption of omega-6 fatty acids, prevalent in vegetable oils, was associated with an increased risk of developing AMD.
Information from http://www.allaboutvision.com/ |
