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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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More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.

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An identified risk factor for osteoporosis is the intake of excessive amounts of vitamin A. Dietary intake of approximately double the recommended daily amount of vitamin A, by women, has been shown to reduce bone mineral density and increase the chances for hip fractures compared with women who consumed the recommended daily amount (or less) of vitamin A.

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People about to have surgery must tell their health care providers about all supplements they take.

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Before a vaccine is licensed in the USA, the Food and Drug Administration (FDA) reviews it for safety and effectiveness. The CDC then reviews all studies again, as well as the American Academy of Pediatrics and the American Academy of Family Physicians. Every lot of vaccine is tested before administration to the public, and the FDA regularly inspects vaccine manufacturers' facilities.

The carbon cycle. Numbers are storage as 1015 g or fluxes as 1015 g per year (data from Schlesinger The carbon cycle. Numbers are storage as 1015 g or fluxes as 1015 g per year (data from Schlesinger
Summary of US Census Data Summary of US Census Data
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Organizing Drug Information by Pharmacologic Classification Organizing Drug Information by Pharmacologic Classification
Electronic service information is available from aftermarket sources, such as All-Data and ... Electronic service information is available from aftermarket sources, such as All-Data and ...
U.S. Subsurface Coal Mining: Output, Price, and Output per Worker-Hour, 1949–1994 U.S. Subsurface Coal Mining: Output, Price, and Output per Worker-Hour, 1949–1994
Video: Cell mediated immune response to a viral infection Animation

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