1) The ciliary muscle to which eye lens is attached and helps to change its focal length by changing radii of curvature of eye lens.
2) When the eye is focussed on a distant object, the ciliary muscles are relaxed so that the focal length of eye lens has its maximum value which is equal its distance from the retina.
3) When the eye is focussed on a closer object the ciliary muscles are strained and focal length of eye lens decreases. The ciliary muscles adjust the focal length in a such a way that the image is formed on retina.
4) This process of adjusting focal length is called accommodation.
5) Ciliary muscles are useful to see distant, closer objects clearly.