**Core Concept**
The zonula of Zinn is a fibrocartilaginous ring that provides structural support to the eyeball, specifically at the junction of the sclera and the ciliary body. It plays a crucial role in maintaining the shape of the eye and facilitating the movement of the lens.

**Why the Correct Answer is Right**
The zonula of Zinn is a fibrocartilaginous ring that encircles the optic nerve as it exits the eyeball. It is composed of collagen and elastic fibers, which provide flexibility and support to the surrounding tissues. The zonula of Zinn is an essential component of the suspensory ligament of the lens, which helps to maintain the shape of the lens and facilitate accommodation.

**Why Each Wrong Option is Incorrect**
**Option A:** The zonula of Zinn is not a part of the suspensory ligament of the iris.
**Option B:** The zonula of Zinn is not a structure that provides support to the retina.
**Option C:** The zonula of Zinn is not a type of ciliary muscle.

**Clinical Pearl / High-Yield Fact**
The zonula of Zinn is an important landmark in ophthalmic surgery, particularly during procedures involving the ciliary body or the lens. It is essential to preserve the integrity of the zonula of Zinn to maintain the structural stability of the eyeball.

**Correct Answer:** C.