(i) When we see distant objects, the ciliary muscles relaVexpand to decrease the curvature and thereby increase the focal length of the lens. Hence, the lens becomes thin. This enables us to see the distant object clearly. Thus, the focal length of the eye lens increases while seeing distant objects.
(ii) To see the nearby objects clearly, the focal length of the lens should be shorter. For this, the ciliary muscles contract to increase the curvature and thereby decrease the focal length of the lens Hence, the lens becomes thick. This enables you to see the nearby objects clearly.
A normal eye is not able to see distinctly the objects placed closer than 25 cm, without putting any strain on the eye. This is because the ciliary muscles of eyes are unable to contract beyond a certain limit. If the objects are placed at a distance of less than 25 cm from the eye, then the objects appear blurred because light rays coming from the object meet beyond the retina.
