Final answer:
The ciliary muscles control the shape of the lens in the eye, allowing for accommodation, which is the adjustment of focal length to focus on objects at different distances.
Step-by-step explanation:
The function of the ciliary muscles in the eye is to control the shape of the lens. These muscles attach to the lens and contract or relax to change its curvature, thereby adjusting the lens's focal length. This process, known as accommodation, allows us to focus on objects at various distances.
The ciliary muscles do not make a hole in the iris nor carry impulses from the rods and cones; those functions involve different parts of the eye: the pupil and the optic nerve, respectively. Nor do the ciliary muscles refract light; refraction primarily occurs when light passes through the cornea and then is fine-tuned by the lens as it focuses light onto the retina, the light-sensitive layer that contains rods and cones.