What controls accommodation by changing the shape of the crystalline lens?

Accommodation refers to the process by which the eye adjusts its focus on near and far objects, primarily involving the crystalline lens. The ciliary muscle plays a crucial role in this process. When the ciliary muscle contracts, it releases tension on the zonules (fibers that connect the ciliary body to the lens), allowing the lens to become more rounded. This rounded shape increases the lens's refractive power, enabling the eye to focus on closer objects.

Conversely, when the ciliary muscle relaxes, tension is increased on the zonules, which flattens the lens and decreases its refractive power, aiding in the focus on distant objects. This ability to change the lens's shape is critical for clear vision at varying distances.

The other components mentioned—pupil, cornea, and sclera—do not have the same function in the process of accommodation. The pupil controls the amount of light entering the eye, the cornea primarily provides most of the eye's optical power, and the sclera offers structural support but does not change shape to aid focus.