If the eye over converges and the light rays focus before they reach the retina, this is called nearsighted person. A nearsighted person can see nearby objects well, but for distant objects, it is hard for person to see clear. Therefore, to help nearsighted person to see clear they should wear glasses or contact lenses. The shape of lens help human eye changes the direction of the incoming light rays so the refractions in the eye have a clear image on the retina. So the shape of the lens is important because different kinds of lenses fix different kinds of problem.

Concave lenses are helping nearsighted people to correct their vision. They are thicker on the edges than in the middle. The following are the diagram to show you how the concave lenses work.