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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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The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
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Parkinson's disease is both chronic and progressive. This means that it persists over a long period of time and that its symptoms grow worse over time.
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Asthma cases in Americans are about 75% higher today than they were in 1980.
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Long-term mental and physical effects from substance abuse include: paranoia, psychosis, immune deficiencies, and organ damage.