Cataract is clouding of the lens in the eye.
Normally light enters the eye from the front, passes through a clear lens, and reaches the retina so one can see. If the lens becomes cloudy, light cannot pass through properly leading to blurred vision.
Most people with cataracts have it in both eyes. However, one eye may be worse than the other because each cataract develops at a different rate. The rate of progression also varies from person to person. In most, the cataract slowly becomes increasingly dense over years, but in others it may mature in a shorter time.