Define accommodation. which part of the eye serves this function? how does its shape change with the distance between you and the object you are looking at?

Accommodation is the ability in which the eye changes its focus from viewing distant objects and then near objects and vice-versa.

The optics and the focal length of the eye are adjusted such that the focus of the retina is on the object even if the distance varies from the eye. It is like a reflux which can be controlled consciously. The process is a consequence of the changes in the zonal tension which is induced by the contractions of the ciliary muscles.

According to the Helmholtz theory of mechanism, the ciliary muscles that are arranged circularly in the eye relax while viewing a far object. This causes the suspensory ligaments and lens zonules to pull the lens, which flattens it.

When a near object is being viewed, the ciliary muscles contract and loosen up the lens zonules causing the lens to form a thick convex.