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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.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
Side effects from substance abuse include nausea, dehydration, reduced productivitiy, and dependence. Though these effects usually worsen over time, the constant need for the substance often overcomes rational thinking.
Fewer than 10% of babies are born on their exact due dates, 50% are born within 1 week of the due date, and 90% are born within 2 weeks of the date.
In most climates, 8 to 10 glasses of water per day is recommended for adults. The best indicator for adequate fluid intake is frequent, clear urination.