By definition a cataract is an opacity in the lens. For practical purposes, however, the term is best applied to those opacities of the lens that impair sicht.

1. Classification and etiology :Cataracts are classified according to the age of the individual, etiology, and the morphologic characteristics of the opacity.

The mechanism of the development of cataract is unknown. Heredity is an important factor in many instances of congenital cataract, and injury to the lens precedes development of traumatic cataract. Many forms of radiant energy such as infrared rays, X-rays. or radium emanation are known to cause cataract. However, little is known concerning the etiology in the large and important class of senile cataracts.

(a) Congenital cotaracts: These vary in size, shape, location, and density. They occur in one eye or both and are usually non-progressive.

(b) Traumatic cataract: This occurs as a result of injury. Starting as a localized opacity the cataract progresses to complete opacification of the lens. a mature cataract.

(C) Complicated cataract: This occurs as a result of various intraocutar diseases such as uveitis, retinitis pigmentosa, or high myopia.

(d) Senile cataract:This occurs in older age groups in eyes that are otherwise quite healthy. The majority of individuals beyond the age of 6o develop lenticular opacities of various types involving the periphery of the lens. and a relatively small number of these individuals develop senile cataracts. Senile cataracts can generally be classified as cortical or nuclear depending on whether the opacification begins in the cortex or in the nucleus of the lens. The two types may develop together in the same lens.

(e) Miscellaneous cataracts:Cataracts also occur as a result of toxic effects of chemicals, from ionizing radiation. in metabolic disorders such as diabetes mellitus and parathyroid tetany, and with neurologic disease such as myotonic dystrophy.

2. Symptoms and signs:The principal symptom of developing cataract is faiting vision. In the course of the development of the nuclear sclerotic type of senile cataract halos of rainbow colors around lights are trequently observed.

Stages of cataract development are classified as incipient, immature,mature, and hypermature. according to the degree and extent of opacification. Within certain limits visual acuity can be correlated with the stage of cataract development, and it is trequently important to be able to state whether a given cataract is sufficient to account for the degree of visual impairment in an eye. In the hypermature stage the cataract may swell and cause glaucoma, or toxic liquefied cortex may seep through the capsule causing iritis. Visual impairment is slight to moderate in the incipient stage. moderate to marked in the immature stage. and marked in the mature and hypermature stage where vision is reduced to light projection. This is the ability to state from what direction a light is coming when a small pocket flash light is held in various places before the eye. Failure to project the light accurately suggests a lesion posterior to the cataract.

3. Diagnosis:The diagnosis of cataract is made by ophthalmoscopic examination, observing the opacities as spots against the background of the fundus reflex. Their location in the lens is determined by parallax and lack of motion except as the eye moves. As the cataract increases fundus details are obscured and gradually lost to view* in a duil reddish retlex which passes through stages of dark red to gray to black when the cataract is in a mature stage. In the late stages the cataract is readily visible with a flashlight as a grayish white or white pupillary reflex.

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