A cataract is a clouding of the normally clear lens of the eye. It may vary in its severity from a small amount of clouding to dense areas of haziness.
A cataract is usually an age-related condition, which disturbs the passage of light and prevents the eye from focussing correctly. The lens is situated behind the iris (the coloured part of the eye). Its purpose is to bend light rays so that they provide a clear image to the retina at the back of the eye.