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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.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
More than one-third of adult Americans are obese. Diseases that kill the largest number of people annually, such as heart disease, cancer, diabetes, stroke, and hypertension, can be attributed to diet.
Multiple sclerosis is a condition wherein the body's nervous system is weakened by an autoimmune reaction that attacks the myelin sheaths of neurons.
Once thought to have neurofibromatosis, Joseph Merrick (also known as "the elephant man") is now, in retrospect, thought by clinical experts to have had Proteus syndrome. This endocrine disease causes continued and abnormal growth of the bones, muscles, skin, and so on and can become completely debilitating with severe deformities occurring anywhere on the body.