The lens is made mostly of water and protein. Specific proteins within the lens are responsible for maintaining its clarity. Over many years, the structures of these lens proteins are altered, ultimately leading to a gradual clouding of the lens. Rarely, cataracts can present at birth or in early childhood as a result of hereditary enzyme defects, and severe trauma to the eye, eye surgery, or intraocular inflammation can also cause cataracts to occur earlier in life. Other factors that may lead to development of cataracts at an earlier age include excessive ultraviolet-light exposure, diabetes, smoking, or the use of certain medications, such as oral, topical, or inhaled steroids. Other medications that are more weakly associated with cataracts include the long-term use of statins and phenothiazines.
Types of Cataracts
All cataracts are fundamentally a change in the clarity of the overall lens structure; however, cataracts may result either early in life or as a result of aging, and different portions of the lens may be more affected than others. Cataracts that occur at birth or present very early in life (during the first year of life) are termed congenital or infantile cataracts. These cataracts require prompt surgical correction or they may prevent the vision in the affected eye from developing normally. When the central portion of the lens is most affected, which is the most common situation, these are termed nuclear cataracts. The outside of the lens is called the lens cortex, and when opacities are most visible in this region, the cataracts are called cortical cataracts. There is an even more specific change that occasionally happens, when the opacity develops immediately next to the lens capsule, either by the anterior, or more commonly the posterior, portion of the capsule; these are called subcapsular cataracts. Unlike most cataracts, posterior subcapsular cataracts can develop rather quickly and affect vision more suddenly than either nuclear or cortical cataracts.
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Having cataracts is often compared to looking through a foggy windshield of a car or through the dirty lens of a camera. Cataracts may cause a variety of complaints and visual changes, including blurred vision, difficulty with glare (often with bright sun or automobile headlights while driving at night), dulled color vision, increased nearsightedness accompanied by frequent changes in eyeglass prescription, and occasionally double vision in one eye. Some people notice a phenomenon called "second sight" in which one's reading vision improves as a result of their increased nearsightedness from swelling of the cataract. A change in glasses may help initially once vision begins to change from cataracts; however, as cataracts continue to progress and opacify, vision becomes cloudy and stronger glasses or contact lenses will no longer improve sight.
Cataracts are usually gradual and usually not painful or associated with any eye redness or other symptoms unless they become extremely advanced. Rapid and/or painful changes in vision are suspicious for other eye diseases and should be evaluated by an eye-care professional.
Last Reviewed 11/17/2017
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