By definition a cataract is an opacity in the lens. For practical purposes, however, the term is only applied to those opacities of the lens that impair sight.
Classification and Etiology: Cataracts are classified according to the age of the individual, etiology, and the morphologic characteristics of the opacity.
The developing mechanism of cataract is unknown. Heredity is an important factor in many instances of congenital cataract, and development of traumatic cataract follows injury to the lens. Many forms of radiant energy such as infrared rays, X-rays, or radium emanation are known to cause cataract. However, little is known about the etiology in the large and important group of senile cataracts.
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