A cataract is a condition that causes a progressive cloudiness of vision. It is most common in older patients, but it can also be congenital. Lens cloudiness, or turbidity, prevents an image from being projected onto the retina. Cataracts are classified by degree of turbidity into cortical, nuclear or subcapsular cataracts. The only way to treat this condition is to replace the clouded lens with an artificial, intraocular lens.