The lens is a transparent structure behind the iris, the coloured part of the eye. The lens bends light rays so that they form a clear image at the back of the eye – on the retina. As the lens is elastic, it can change shape, getting fatter to focus close objects and thinner for distant objects.
Once the natural lens in the eye has been removed, the eye loses its ability to focus light and images clearly on to the retina, the light-sensitive tissue that lines the inside surface of the eye. Before the development of artificial lenses, hard contact lenses or very thick eyeglasses were the only options for correcting vision after cataract surgery.