Description and symptoms
The human lens is positioned directly behind the iris. The iris is the colored tissue (blue, hazel, green, or brown) that opens and closes to form the ever changing pupil. The lens itself is basically a disc, with a cellophane like outer coating and clear jelly within. For a variety of reasons including increasing age, genetic predisposition, trauma, ultraviolet light, systemic diseases (diabetes), systemic medication, that clear jelly deteriorates in various parts of the lens causing a number of different visual symptoms. The process of the deterioration of the lens is called cataractous degeneration, making the lens a cataract or in common parlance a cataract. Opacification or cloudiness throughout the lens will cause an overall reduction in visual perception i.e. Blurred vision. Opacification in the front of the lens will cause increasing glare, rings around lights, and occasional monocular diplopia (double vision). Central "browning" of the lens causes color distortion, a sense of needing more light, and occasionally increasing myopia or near-sightedness. Opacification toward the back of the lens is generally rapid in development and initially causes a severe loss of reading vision. Cataractous degeneration is always progressive, although at varying rates of development even between two eyes in the same head. The only cure for cataractous degeneration is surgery.

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