Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss in the United States.
AMD is a progressive and degenerative disease affecting the central part of the retina, the macula.
Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss in the United States. Its prevalence is increasing with the growth of our aging population. In the U.S., over, 11 million people suffer from AMD (1.75 million individuals have advanced forms of AMD). The worldwide prevalence of AMD is estimated to be at 196 million people and is estimated to increase to 288 million by 2040.
The macula is a structure in your retina that is responsible for central vision (i.e. sharp vision). Your central vision is critical in activities such as driving and reading which requires sharp vision to see fine details clearly. Vision loss caused by AMD typically starts with a blurred area near the central part of your vision. Over some period of time, the blurred spot may grow larger or you may develop blank spots in your central vision. Also, objects may not appear to be as bright as they once were. AMD progresses at different rates in people. Some have AMD progress so slowly that vision loss does not occur for a longer period of time. In others, AMD may progress quickly to lead to vision loss in one or both eyes.
While the visual impact associated with early and intermediate stages of AMD can be minimal, some affected individuals progress to advanced disease. These advanced subtypes of geographic atrophy (GA) and neovascular disease (NV) are commonly associated with visual impairment and blindness, affecting quality of life and leading to loss of independence.
People at Risk
The causes of AMD are multifactorial, and both behavioral and genetic risk factors contribute to personal risk. AMD is an age-related disease and is the leading cause of blindness among the elderly. Other significant risk factors that have been implicated in causing AMD includes:
Age: AMD is an age-related disease and most common to occur after the age of 55
Genetics: having a family history of AMD puts you at highest risk.
Smoking: doubles the risk of AMD
Nutrition: poor diet and obesity can increase AMD. Omega-3 fatty acid intake can help slow the progression
Race: more common in Caucasians
Stages of AMD
There are three main stages of AMD. Each stage is defined in part by the size and number of drusen under the retina. Drusen are yellow deposits made up of lipids (a fatty protein) under the retina. It is possible to have AMD in one eye only, or to have one eye with a later stage of AMD than the other.
Early AMD. Early AMD is diagnosed by the presence of medium-sized drusen, which are about the width of an average human hair. People with early AMD typically do not have vision loss.
Intermediate AMD. People with intermediate AMD typically have large drusen, pigment changes in the retina, or both. Again, these changes can only be detected during an eye exam. Intermediate AMD may cause some vision loss, but most people will not experience any symptoms.
Late AMD. In addition to drusen, people with late AMD have vision loss from damage to the macula.
There are two types of late AMD:
In geographic atrophy (also called dry AMD), there is a gradual breakdown of the light-sensitive cells in the macula that convey visual information to the brain, and of the supporting tissue beneath the macula. These changes cause vision loss.
In neovascular AMD (also called wet AMD), abnormal blood vessels grow underneath the retina. (“Neovascular” literally means “new vessels.”) These vessels can leak fluid and blood, which may lead to swelling and damage of the macula. The damage may be rapid and severe, unlike the more gradual course of geographic atrophy. It is possible to have both geographic atrophy and neovascular AMD in the same eye, and either condition can appear first.
Testing and Treatment
There is a high treatment burden of AMD. Patients with advanced NV are treated with anti–vascular endothelial growth factor (VEGF) eye injections. These injections can be an effective treatment for many patients. Unfortunately, some patients do not respond, and visual loss continues over time. There is no treatment for GA. Thus, prevention of advanced disease and finding new and effective treatments remains a significant challenge. Identifying individuals with early and intermediate disease at high risk of progression to advanced stages would lead to earlier intervention and reduced burden of visual loss due to AMD.
It is estimated that genetics is the cause of AMD in about 60-80% of the cases. For those people who are at high risk due to a positive family history or having signs of early or intermediate disease, are among the highest risk of progressing to advanced stages of AMD with visual loss.
For these individuals, early detection could reduce the risk of AMD by targeting and emphasizing modifiable habits earlier in life and recommending more frequent surveillance for those highly susceptible to the disease.
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Investigative Ophthalmology & Visual Science, May 2009, Vol. 50, No. 5