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A cataract is a clouding of the lens in the eye leading to a decrease in vision. It can affect one or both eyes. Often it develops slowly. Symptoms may include faded colors, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night.〔(【引用サイトリンク】url=https://www.nei.nih.gov/health/cataract/cataract_facts )〕 This may result in trouble driving, reading, or recognizing faces. Poor vision may also result in an increased risk of falling and depression. Cataracts are the cause of half of blindness and 33% of visual impairment worldwide.〔(【引用サイトリンク】url=http://www.who.int/mediacentre/factsheets/fs282/en/ )〕 Cataracts are most commonly due to aging, but may also occur due to trauma, radiation exposure, be present from birth, or occur following eye surgery for other problems.〔〔(【引用サイトリンク】url=http://www.who.int/blindness/causes/priority/en/index1.html )〕 Risk factors include diabetes, smoking tobacco, prolonged exposure to sunlight, and alcohol. Either clumps of protein or yellow-brown pigment may be deposited in the lens reducing the transmission of light to the retina at the back of the eye. Diagnosis is by an eye examination.〔 Prevention includes wearing sunglasses and not smoking. Early on the symptoms may be improved with eyeglasses. If this does not help, surgery to remove the cloudy lens and replace it with an artificial lens is the only effective treatment. Surgery is only needed if the cataracts are causing problems.〔 Surgery generally results in an improved quality of life. Cataract surgery is not easily available in many countries, which is especially true for women.〔〔 About 20 million people globally are blind due to cataracts.〔 It is the cause of about 5% of blindness in the United States and nearly 60% of blindness in parts of Africa and South America. Blindness from cataracts occurs in about 10 to 40 per 100,000 children in the developing world and 1 to 4 per 100,000 children in the developed world. Cataracts become more common with age. About half the people in the United States have had cataracts by the age of 80.〔 == Signs and symptoms == Signs and symptoms vary depending on the type of cataract, though considerable overlap occurs. People with nuclear sclerotic or brunescent cataracts often notice a reduction of vision. Those with posterior subcapsular cataracts usually complain of glare as their major symptom. The severity of cataract formation, assuming no other eye disease is present, is judged primarily by a visual acuity test. The appropriateness of surgery depends on a patient's particular functional and visual needs and other risk factors, all of which may vary widely. 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「cataract」の詳細全文を読む スポンサード リンク
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