Cataract is a disorder characterised by the loss of transparency and development of opacity in the natural eye lens, which is located behind the eye pupil which maintains eyesight. In other words, it can be defined as a disruption of eyesight as if the patient looks on the world from behind a misted pane of glass.

While typically seen in people above the middle age range, cataract can also be seen in new-borns, diabetics, due to trauma and in people who take long-term cortisone medication.