This is due to the ability, of the eye lens to adjust its focal length which is little n as accommodation. When the ciliary muscles are relaxed, the lens becomes thin. -thus, it's focal length increases. This enables us to see distant objects clearly. When we are looking at objects closer to the eye, the ciliary muscles contract. This increases the curvature of the eye lens. the eye lens becomes thicker. The focal length of the eye lens decreases. This enables us to see nearby objects clearly.
