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

Cataracts—what are they, and what causes them?

By Dr. Sonja Iverson-Hill

HTF Contributor
Virginia: The most common cause of vision loss in people over the age of 40 is cataracts.
In fact, according to Prevent Blindness America (PBA) over half of all Americans will have 
cataracts by the time they are 80 years old. Cataracts, however, are a natural aging process
of the eye. The lens, which is located behind the iris, becomes more opaque and cloudy
causing vision to be hazy and blurry. Similar to a camera lens which needs to be clean in
order to take a clear picture, the lenses inside our eyes also need to be clear in order for
our vision to be sharp. While some find it particularly difficult to accomplish simple daily 
tasks…. More: 
 Source: Hometown Focus