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Astigmatism is the most common vision problem. It may accompany nearsightedness or farsightedness. It is usually caused by an irregularly shaped cornea, but sometimes it is the result of an irregularly shaped lens. Either type can be corrected by eyeglasses, contact lenses, or refractive surgery.
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Thyroid conditions cause a higher risk of fibromyalgia and chronic fatigue syndrome.
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Vaccines prevent between 2.5 and 4 million deaths every year.
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Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
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A seasonal flu vaccine is the best way to reduce the chances you will get seasonal influenza and spread it to others.