Accommodation is the ability or property of the eye lens to change its curvature or focal length so that images of objects at various distances can be formed on the same retina. Ciliary muscles help in changing the focal length.

Viewing Of Far Off Objects: When the ciliary muscles are completely relaxed, the eye lens is thin and its focal length is maximum (equal to distance between retina and eye lens).The rays which are coming from the distant object are parallel to each other and they are focused at the retina. Formation of image on retina is illustrated in the figure below.

Viewing nearby Objects: Ciliary muscles contract when we look at nearby objects. The eye lens bulges out and becomes thick. Focal length is reduced as a result. This focuses light from the nearby object on retina as shown in the figure below.