A cataract is a clouding of the lens in the eye that affects vision, mostly related to aging and can occur in either or both eyes but cannot spread from one eye to another.  Certain risk factors for cateracts include age, certain diseases/health problems (such as diabetes), personal behavioral choices (such as steriod, alcohol, or tobacco use), environment (prolonged exposure to ultraviolet light), eye injury (in some cases, and sometimes years later), and sometimes after eye surgery.