**Core Concept**
A Vossius ring is a circular, semi-lunar or ring-shaped opacity seen on the anterior surface of the cornea. It occurs due to a contusion of the cornea, typically caused by a blunt trauma to the globe. The ring is formed due to the compression of the corneal stroma against the endothelium.

**Why the Correct Answer is Right**
When a blunt trauma occurs to the eye, the force compresses the corneal stroma against the endothelium, creating a ring-shaped opacity. This is because the endothelium is a fixed layer, whereas the stroma is more pliable. As a result, the stroma is compressed, creating the characteristic Vossius ring. The ring is usually seen on the anterior surface of the cornea and can be a diagnostic feature of blunt trauma.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Vossius ring is not a feature of penetrating trauma, which typically results in a different type of corneal injury.
**Option B:** This option is incorrect because Vossius ring is not a feature of keratoconus, which is a condition characterized by a thinning and conical protrusion of the cornea.
**Option C:** This option is incorrect because Vossius ring is not a feature of Fuchs' endothelial dystrophy, which is a condition characterized by a degeneration of the endothelium.

**Clinical Pearl / High-Yield Fact**
A Vossius ring is an important diagnostic feature of blunt trauma to the eye, and its presence should prompt a thorough investigation into the mechanism of injury.

**Correct Answer: C.**