Cataracts occur when the lens inside of the eye responsible for focusing the image on the retina becomes cloudy.
It is not hereditary and it is not a growth in the eye. It is a change in the eye where the naturally clear lens becomes cloudy: like looking through a dirty window. In the early stages you might not have any symptoms; but as the cataract progresses the vision will begin to get blurry and glasses will not fix the problem. Cataracts mainly occur as you get older normally after the age of 60; they can however occur earlier or secondary to trauma.
Cataracts are only correctable by surgery. This involves removing the natural cloudy lens of the eye and replacing it with a clear artificial lens, known as an Intra-Ocular Lens.
Eye Without Cataract
Eye With Cataract