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Normal vision. Courtesy NIH National Eye Institute
The same view with a cataract.
A cataract is any opacity which develops in the crystalline lens of the eye or in its envelope. Cataracts form for a variety of reasons, including infrared and microwave exposure, secondary effects of diseases such as diabetes, or simply due to advanced age; they are usually a result of denaturation of lens proteins. Genetic factors are often a cause of congenital cataracts and may also play a role in predisposing someone to cataracts. Traumatic cataracts are produced by injuries to the eye.
Cataracts may be partial or complete, stationary or progressive, hard or soft. An early technique to remove cataracts was couching, which involved using a thin needle to remove the clouding. This technique is known to have existed in Roman times and continued to be used throughout the Middle Ages and continues to be used in Third World countries today.
The most effective and common treatment for cataracts is surgery to remove the cloudy lens. There are two types of surgery that can be used to remove cataracts, extra-capsular and intra-capsular surgery. Extra-capsular surgery consists of removing the lens but leaving the back half of the lens capsule intact. High frequency sound waves ( phacoemulsification) are sometimes used to break up the lens before extraction. Intra-capsular surgery involves removing the entire lens of the eye, including the lens capsule, but it is performed quite rarely nowadays. The lens is then replaced with a plastic lens (an intraocular lens implant) which remains permanently in the eye.
Cataract operations are mostly performed under a local anaesthetic and the patient will be allowed to go home the same day. Complications after cataract surgery are uncommon. Many people (up to 50%) can develop a posterior capsular opacification after initial cataract surgery. This is a thickening and clouding of the lens capsule (which was left behind when the cataract was removed) and it can be easily corrected using a laser to make holes in the capsule for the person to see through.
Human eye cross-sectional view. Courtesy NIH National Eye Institute
Cataract is also used to mean a waterfall or where the flow of a riverMurray River in Australia Australia A river is a large natural waterway. It is a specific term in the vernacular for large streams, stream being the umbrella term used in the scientific community for all flowing natural waterways. In the vernacular, strea changes dramatically. It comes from the GreekThe Greek language ( /Elini'k{/) is an Indo-European language which has existed from around the 14th century BC in the Cretan inscriptions called Linear B. Mycenaean Greek of this period is distinguished from later Classical or Ancient Greek of the 8th ce word meaning "downrush" or "to dash down" or the Latin "cataract" meaning a waterfall, a floodgate or a portcullisA portcullis is a grille or gate made of wood, metal or a combination of the two. Portcullises fortified the entrances to many medieval castles, acting as a last line of defence during time of attack or siege. Each portcullis was mounted in vertical groov.
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