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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.
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).
It is believed that humans initially contracted crabs from gorillas about 3 million years ago from either sleeping in gorilla nests or eating the apes.
Nearly 31 million adults in America have a total cholesterol level that is more than 240 mg per dL.
![In early industrialization, children worked alongside adults. They worked 12 hours a day Monday to ...](https://biology-forums.com/gallery/27/medium_660366_13_04_17_6_20_49_27692552.png)
![Children with disabilities used to be sent to special schools. In a process called mainstreaming or ...](https://biology-forums.com/gallery/27/medium_482573_20_04_17_1_00_31_27949851.png)