cataracts occur when the natural clear lens inside the eye located behind the iris becomes cloudy over time. this lens is important for focusing light on the back of the eye (the retina) so that images appear clear and without distortion and the clouding of this lens during cataract formation distorts vision. cataracts are usually a very gradual process of normal aging but can occasionally develop rapidly. they commonly affect both eyes but it is not uncommon for a cataract in one eye to advance more rapidly. cataracts are very common affecting roughly 60% of people over the age of 60 and over 1. 5 million cataract surgeries are performed in the united states each year. precisely why cataracts occur is unknown; however most cataracts appear to be caused by changes in the protein structures within the lens that occur over many years and cause the lens to become cloudy. rarely cataracts can be present at birth or in early childhood as a result of hereditary enzyme defects. severe trauma to the eye eye surgery or intraocular inflammation can also cause cataracts to develop more rapidly. other factors that may lead to the 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. experts have estimated that in the united states visual disability associated with cataracts accounts for over 8 million physician office visits a year. this number will likely continue to increase as the proportion of people over the age of 60 rises. when people develop cataracts they begin to have difficulty doing activities they enjoy. some of the most common complaints include difficulty driving at night reading or traveling. these are all activities for which clear vision is essential.
what is a cataract?