What is the role of the ciliary muscle?

The ciliary muscle plays a crucial role in the process of accommodation, which alters the shape of the lens to enable clear vision at varying distances. When it contracts, it allows the lens to become more rounded, which is necessary for focusing on nearby objects. This action is directly associated with the opening and closing of the pupil because the muscle impacts the pupil size indirectly through changes in the lens shape and the amount of light entering the eye.

The correct answer reflects the ciliary muscle's function in modulating the eye's optical system, thereby supporting the mechanism of adjusting the pupil size to control light entry. While the options offer multiple roles relating to vision, focusing primarily on optical adjustments is aligned with the ciliary muscle's main function. Other options relate to different components of the eye or physiological functions not directly associated with the ciliary muscle.