The ability of the eye lens to adjust its focal length is called accommodation.

When the ciliary muscles of our eyes are relaxed, the eye lens becomes thin. This results in an increase in the focal length, making distant objects clearly visible to the eyes.

When the ciliary muscles contract, our eye lens becomes thick. This results in a reduction of the focal length of the eye lens, and nearby objects become visible to the eyes.

Therefore, the focal length can be adjusted by the human eye lens to view both distant and nearby objects on the retina.