Home Cataracts Cataracts occur when changes in the lens of the eye cause it to become less transparent. This results in cloudy or misty vision. Cataracts are the leading cause of blindness globally. The good news is that they are entirely treatable with around 350,000 cataract operations performed by the NHS every year. The operation is generally very safe and takes little more than 15 minutes to complete. Cataracts interfere with the passage of light through the lens of the eye. The lens is a crystalline structure that sits just behind the pupil - the black circle in the centre of the eye through which light enters. The light is focused by the cornea and the lens on the retina, a layer of light-sensitive cells at the back of the eye, which creates an electrical interpretation of the image which is transmitted to the brain, enabling us to see. Cataracts most often start to develop in a person's lens as they get older, stopping some of the light from reaching the back of the eye. Over time, cataracts become worse and start to affect vision. Eventually, surgery is needed to remove and replace the affected lens.