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Macular degeneration, often age-related macular degeneration (AMD or ARMD), is a medical condition that usually affects older adults and results in a loss of vision in the center of the visual field (the macula) because of damage to the retina. It is a major cause of blindness and visual impairment in older adults, afflicting 30-50 million people globally. Macular degeneration can make it difficult or impossible to read or to recognize faces, although enough peripheral vision remains to allow other activities of daily life. Although some macular dystrophies affecting younger individuals are sometimes rarely referred to as macular degeneration, the term generally refers to age-related macular degeneration (AMD or ARMD). It occurs in "dry" form resulting from atrophy and scarring, and (less commonly) "wet" form, resulting from abnormal vascularization. Macular degeneration is caused by advancing age, genetic predisposition and cumulative environmental and lifestyle damage, in particular smoking. It is also associated wth several cardiovascular risk factors. There is no cure, no treatment that can restore lost vision, and no specific preventatives. Antiangiogenic drugs injected directly into the eye, or in limited special cases, laser coagulation or photodynamic therapy may slow progression of the wet form of AMD. Research is ongoing in the area of dietary changes and supplements to slow progression of the disease. Diagnosis is by signs in the macula like accumulation of plaque-like deposits called drusen, pigmentation changes, or neovascularity. Like many age-related disorders, macular degeneration was once rare, but has become increasingly common in developed nations in the last 30 years due to the rapid growth in the number of people over 75 and poses a significant health care challenge as it is the most common cause of vision loss in adults, with the bulk of new cases occurring after the age of 80. By 2020, it is estimated that as many as 3 million Americans will be affected.〔http://www.sfgate.com/health/article/Macular-degeneration-a-growing-problem-3822617.php〕 == Signs and symptoms == ] Signs and symptoms of macular degeneration include: Visual symptoms *Distorted vision in the form of metamorphopsia, in which a grid of straight lines appears wavy and parts of the grid may appear blank: Patients often first notice this when looking at things like miniblinds in their home or telephone poles while driving. There may also be central scotomas, shadows or missing areas of vision *Slow recovery of visual function after exposure to bright light (photostress test) *Visual acuity drastically decreasing (two levels or more), e.g.: 20/20 to 20/80 *Blurred vision: Those with nonexudative macular degeneration may be asymptomatic or notice a gradual loss of central vision, whereas those with exudative macular degeneration often notice a rapid onset of vision loss (often caused by leakage and bleeding of abnormal blood vessels). *Trouble discerning colors, specifically dark ones from dark ones and light ones from light ones *A loss in contrast sensitivity Macular degeneration by itself will not lead to total blindness. For that matter, only a very small number of people with visual impairment are totally blind. In almost all cases, some vision remains, mainly peripheral. Other complicating conditions may possibly lead to such an acute condition (severe stroke or trauma, untreated glaucoma, etc.), but few macular degeneration patients experience total visual loss. The area of the macula comprises only about 2.1% of the retina, and the remaining 97.9% (the peripheral field) remains unaffected by the disease. Even though the macula provides such a small fraction of the visual field, almost half of the visual cortex is devoted to processing macular information. The loss of central vision profoundly affects visual functioning. It is quite difficult, for example, to read without central vision. Pictures that attempt to depict the central visual loss of macular degeneration with a black spot do not really do justice to the devastating nature of the visual loss. This can be demonstrated by printing letters six inches high on a piece of paper and attempting to identify them while looking straight ahead and holding the paper slightly to the side. Most people find this difficult to do. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Macular degeneration」の詳細全文を読む スポンサード リンク
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