What is the primary function of the ciliary body?

The primary function of the ciliary body is to produce the aqueous humor, which is a clear fluid found in the anterior chamber of the eye. This fluid plays a critical role in maintaining intraocular pressure, providing nutrients to the avascular structures of the eye (like the lens and cornea), and helping to remove metabolic wastes. The ciliary body is also involved in the accommodation process, which allows the lens to change shape and focus on objects at different distances. While the aqueous humor production is one of its key roles, its ability to affect the tension of the zonules surrounding the lens further supports its function in vision.

The other answer choices do not accurately reflect the roles of the ciliary body. For instance, eye color is determined by the pigmentation of the iris, which is separate from the ciliary body's functions. The ciliary body does not provide protection to the retina directly; instead, that role is primarily handled by other structures within the eye. Lastly, the shape of the cornea is largely fixed and not altered by the ciliary body; it is influenced by different tissues and its anatomical structure rather than the functions of the ciliary body.