A cataract is a clouding of the lens of the eye, which is typically clear. For people who have cataracts, seeing through cloudy lenses is like looking through a frosty or fogged-up window. Clouded vision caused by cataracts can make it more difficult to read, drive a car at night, or see the expression on a friend's face. Most cataracts develop slowly and don't disturb eyesight early on. But with time, cataracts will eventually affect vision.

Source: Mayo Clinic