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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.
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.
The first successful kidney transplant was performed in 1954 and occurred in Boston. A kidney from an identical twin was transplanted into his dying brother's body and was not rejected because it did not appear foreign to his body.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
Thyroid conditions cause a higher risk of fibromyalgia and chronic fatigue syndrome.
![The visual field as seen by a person with (a) glaucoma, (b) macular degeneration, and (c) cataracts.](https://biology-forums.com/gallery/47/medium_33_29_07_11_7_45_50.jpeg)
![In addition to common schools, thousands of female seminaries were built between 1820 and 1850, many](https://biology-forums.com/gallery/47/medium_375348_18_08_15_9_36_30_223031090.jpeg)