A cataract corresponds to the clouding of the lens. The lens is crucial for sight and also for visual accommodation, i.e. the ability to switch between near and far focus.
The commonest cause of cataracts is age and therefore ageing. Also cataract can be related to a pre-existing eye disorder, chronic illnesses or result from eye injury (post-traumatic cataract). In children, cataract can also be congenital.
A number of factors increase the risk of developing cataracts, including smoking, excessive alcohol consumption and exposure to sunlight (ultraviolet rays).