How are we able to see nearby and also the distant objects clearly?

Explanation

We are able to see nearby and also the distant objects clearly due to the ability of the eye lens to adjust its focal length which is known as power of accommodation.
When the muscles are relaxed, the lens becomes thin and its focal length increases. This enables us to see the distant objects clearly. When the ciliary muscles are contract, the curvature of the eye lens increases and the eye lens becomes thicker. Consequently, the focal length of the eye lens decreases. This enables us to see nearby objects clearly.