The lens is a transparent disc located inside the eye, it focuses light rays entering the retina to form a sharp, clear image, like the lens of a camera focuses the image onto film. The lens functions as a 20D converging lens located behind the iris and participates in the accommodation process of the eye.

Cataracts are a common eye problem in older people and a leading cause of blindness. Cataract surgery is the most effective treatment for this condition.