A cataract is a clouding of the natural intraocular crystalline lens that focuses the light entering the eye onto the retina. This cloudiness can cause a decrease in vision and may lead to eventual blindness if left untreated. Cataracts often develop slowly and painlessly, so vision and lifestyle can be affected without a person realizing it. Worldwide, cataracts are the number one cause of preventable blindness. There is no medical treatment to prevent the development or progression of cataracts. Modern cataract surgery, which is the removal of the cloudy lens and implantation of a clear intraocular lens (IOL), is the only definitive treatment for cataracts. Cataract surgery is the most effective and most common procedure performed in all of medicine with 3 million Americans choosing to have cataract surgery each year, and an overall success rate of 97 percent or higher when performed in appropriate settings.