Each year, cataracts affect millions of people, including more than half of all Americans aged 60 and older. A cataract is a painless clouding of the eye’s natural lens that is caused by a buildup of protein. A cataract can form in one or both eyes. If left untreated, cataracts worsen over time and interfere with everyday activities such as reading or driving. Night vision is usually most affected. When cataracts are in their early stages, people are helped by brighter lighting. As cataracts get worse, however, most people require surgery.