Cataract
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Template:DiseaseDisorder infobox | }} Template:For Template:For2 Image:Eyesection.gif Image:Human eyesight two children and ball normal vision.jpg Image:Human eyesight two children and ball with cataract.jpg In ophthalmology, a cataract is any opacity which develops in the crystalline lens of the eye or in its envelope. The name derives from the Latin cataracta meaning "waterfall" and the Greek kataraktes and katarrhaktes, from katarassein meaning "to dash down" (kata-, "down"; arassein, "to strike, dash") [1].
Cataracts form for a variety of reasons, including long-term ultraviolet 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. Some cataract formation is to be expected in any person over the age of 70. Fully half of all people between the ages of 65 and 74 and about 70% of those over 75 have some cataract formation. Cataracts may also be produced by eye injury or physical trauma. A study among Icelandair pilots showed commercial airline pilots as three times as likely to develop cataracts as people with non-flying jobs. This is thought to be caused by radiation coming from outer space [2].
Cataracts may be partial or complete, stationary or progressive, hard or soft.
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Cataract surgery
An early technique to remove cataracts was couching, which involved using a thin needle or stick 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 underprivileged "Third world" countries today. In India, however, modern surgery with intraocular lens insertion in Government and Non Government Organisation (NGO) sponsored Eye Surgical Camps have totally replaced this method.
The most effective and common treatment is cataract 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 majority 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 rarely performed in modern practice. In either extra-capsular surgery or intra-capsular surgery, the lens is replaced with a plastic lens (an intraocular lens implant) which remains permanently in the eye.
Previously, polymethylmethacrylate was used as the lens material. Advances have brought about the use of silicone acrylate which is a soft material. This allows the lens to be folded and inserted into the eye through a smaller incision. Acrylic lenses can also be used with small incisions and are a better choice in people who have a history of uveitis or are at high risk of retinal detachment. Acrylic is not always an ideal choice due to its added expense.
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 possible. In the past many people (up to 50%) developed 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. Modern lens design has reduced the chance of capsular opacification to less than 5%Template:Fact. Retinal detachment is an uncommon complication of cataract surgery.
Prevention
Although cataracts have no scientifically proven prevention, it is sometimes said that wearing ultraviolet-protecting sunglasses may slow the development of cataracts. Regular intake of antioxidants (such as vitamin C and E) is theoretically helpful, but this is also not proven.
Etymology
A cataract is a large waterfall or place where the flow of a river changes dramatically. The term comes from the Greek word kataraktes, whose meaning "to dash down" or "downrush" describes rapidly running water, and the Latin cataracta, whose meaning describes "a waterfall", "a floodgate", or "a portcullis". As rapidly running water turns white, the term was later used metaphorically to describe the similar appearance of mature ocular opacities.
Types of cataracts
- Classified by etiology
- Age-related cataract
- Congenital cataract
- Secondary cataract
- Traumatic cataract
- Classified by location
- Anterior cortical cataract
- Anterior polar cataract
- Anterior subcapsular cataract
- Nuclear cataract
- Posterior cortical cataract
- Posterior polar cataract
- Posterior subcapsular cataract
Associations with systemic conditions
- Disease of the skin and mucous membranes
- Congenital
- Others
- Toxic substances introduced systemically
References
- Pavan-Langston, Deborah (1990). Manual of Ocular Diagnosis and Therapy. Little, Brown and Company.
- Rafnsson V, Olafsdottir E, Hrafnkelsson J, Sasaki H, Arnarsson A, Jonasson F. Cosmic radiation increases the risk of nuclear cataract in airline pilots: a population-based case-control study. Arch Ophthalmol 2005; 123: 1102-1105. Medline Link
See also
External links
- NHS Best Treatments Site
- eMedicine Health
- VisionSimulations.com | Images and vision simulators of various diseases and conditions of the eye
- CureBlindness.org | Non-profit organisation performing cataract surgery in the Himalayas. Restore vision for less than $20.de:Katarakt (Medizin)
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