Which structure in the eye adjusts the shape of the lens to help focusing?

• A. Iris
• B. Ciliary muscles
• C. Cornea
• D. Retina

Answer: (B)

Accommodation is the process by which the eye changes the lens shape to focus on objects at different distances. The structure responsible is the ciliary muscles, which surround the lens. When these muscles contract, they reduce tension on the zonular fibers attached to the lens, allowing the lens to become more rounded and increase its refractive power for near vision. When the ciliary muscles relax, tension on the zonules increases, the lens flattens, and the eye focuses better on distant objects.

The other structures don’t adjust the lens shape: the iris controls the size of the pupil to regulate light entry, the cornea provides most of the eye’s refractive power but doesn’t change shape to adjust focus, and the retina is the light-detecting layer at the back of the eye.