What structure surrounding the lens connects the choroid and iris?

The ciliary body is the correct answer because it is the structure that connects the choroid and the iris within the eye. It plays a critical role in the process of accommodation, allowing the lens to change shape for focusing on objects at various distances. The ciliary body contains the ciliary muscle, which regulates the tension on the zonules that hold the lens in place, facilitating changes in the lens curvature.

The cornea, although essential for refracting light entering the eye, is not located between the choroid and the iris. The iris is actually a part of the anterior segment of the eye and is involved in regulating the amount of light that enters by controlling the size of the pupil, but it does not connect the choroid to anything. The crystalline lens itself is the structure that focuses light but does not serve to connect other structures. Thus, the ciliary body's position and function make it integral to the relationship between the choroid and iris.