When an object is at a distance, the ciliary muscles of the eye get fully relaxed and pull the suspensory ligament attached to the eye-lens tightly. Which then, stretches the eye-lens and the eye-lens becomes thin. This thin eye-lens has large focal length and small converging power sufficient to converge the parallel rays of light coming from a distant object to form an image on the retina.

In the same way, to focus on nearby objects, there is contraction in the ciliary muscles and which make the suspensory ligament loose. The ligaments then stop pulling the eye-lens. The eye-lens bulges under its own elasticity and becomes thick. This thick eye-lens has small focal length and large converging power which converges the diverging rays coming from the nearby object to form an image on the retina.