Cataracts occur when changes in the lens of the eye cause it to become less transparent. The lens is the crystalline structure that sits just behind your pupil, which is the black circle in the centre of your eye.
When light enters your eye, it passes through the transparent layer of tissue at the front of the eye (the cornea) and the lens, which focuses it on the light-sensitive layer of cells at the back of your eye (the retina).
Cataracts sometimes start to develop in a person’s lens as they get older (age-related cataracts), stopping some of the light reaching the retina. This can affect your vision, making it become increasingly cloudy, blurry, or misty.
Although cataracts are often associated with age, in rare cases babies are born with cataracts or young children can develop them (childhood cataracts).