The focal length of the lens of the eye is under the control of:

Correct answer: (a) Ciliary body

Explanation

The ciliary body, through its ciliary muscles, changes the curvature (thickness) of the eye lens and so its focal length. This is called accommodation:

• to see near objects, the ciliary muscles contract, the lens becomes thicker and its focal length shortens;
• to see distant objects, the muscles relax, the lens becomes thinner and its focal length increases.

The iris controls the size of the pupil (how much light enters), and the cornea does most of the bending of light but has a fixed shape.