The change in focal length of an eye lens is caused by the action of the(a) pupil(b) retina(c) ciliary muscles(d) iris

(c) The relaxation or contraction of ciliary muscles changes the curvature of the eye lens. The change in curvature of the eye lens changes the focal length of the eyes. Hence, the change in focal length of an eye lens is caused by the action of ciliary muscles.