Power of accommodation of human eye: The ability of eye lens to adjust its focal length to form the sharp image of the object at a varying distance on the retina is called its power of accommodation. The curvature of eye lens can be changed (i.e. change in its focal length) to some extent by the ciliary muscles.
When we are looking at the nearby objects, the ciliary muscles contract, it increases the thickness of eye lens. The eye lens then becomes thicker. As a result, the focal length of eye lens decreases in such a way that the clear sharp image of the nearby object is formed on the retina. Thus, the object is seen clearly to us. When we are looking at the distant objects, these muscles are in a relaxed position, the eye lens. becomes thinner, the focal length of the lens increases. Therefore, the parallel rays coming from the distant object are focussed on the retina and object is seen clearly to us. Thus, the accommodation power of an eye helps a person to see nearby as well as distant objects clearly.