A cataract is an opacity of the lens of the eye that causes partial or total blindness (picture 1). Cataracts are a common and frequently curable cause of blindness in children. Early detection and prompt intervention are critical for a good visual outcome, particularly in newborns.
Cataracts in infants and children will be reviewed here. Lens dislocation in children and cataracts in adults are discussed separately. (See "Ectopia lentis (dislocated lens) in children" and "Cataract in adults".)
The reported prevalence of childhood cataracts ranges from 1 to 15 per 10,000 children. The wide range reflects differences in populations, age groups, methods of ascertainment, and case definitions . The prevalence of congenital cataract in developed countries is 1 to 3 per 10,000 [1-4].
The crystalline lens consists of five major structures: embryonic nucleus, fetal nucleus, cortex, lens epithelium, and lens capsule . The crystalline lens focuses light rays onto the retina . Relaxation or contraction of the ciliary body changes the shape of the lens to permit focus of light rays from objects at distant and near fixation (figure 1). Contraction of the ciliary body to permit focus at near fixation is referred to as "accommodation".
Cataracts are usually classified according to their location in the lens (figure 2), morphologic appearance (table 1), and/or underlying pathology [6,7]: