(D) The eye lens system functions like a biconvex lens,as it is curved in both sides but flat only at the centre part of the lens. When light rays enter the human eye, the curved surfaces bend them. This process is called refraction.Bending the light rays is necessary in order to focus an external object’s image and emit the light just behind the lens, at an area called the focal point. The image is then focussed on the retina. The image formed is left-right reversed and inverted on the cornea. Also, the image looks smaller than the external object in view.