Question

What changes take place in the shape of eye-lens:
(a) when the eye is focused on a near object?
(b) when the eye is focused on a distant object?

Answer 1

(a) When the eye is focussed on a nearby object, the eye lens bulges and becomes thicker. This is because, when the eye is focussed on a nearby object, the ciliary muscles of the eyes contract, loosening the suspensory ligaments attached to the the eye. As these ligaments become loose, they stop pulling the eye lens, because of which the eye lens bulges (or becomes more convex) so as to increase its converging power.

(b) When the eye is focussed on a distant object, the eye lens gets stretched and becomes thinner. This is because, when the eye is focused on a distant object, the ciliary muscles are completely relaxed. The relaxed ciliary muscles pull the suspensory ligaments tightly. As these ligaments become tight, they pull the eye lens, because of which the eye lens becomes thinner (or less convex).