**Core Concept**
KF ring, also known as Fleischer ring, is a characteristic finding in certain ocular conditions. It refers to a ring-shaped deposit in the Descemet's membrane of the cornea, which is a thin layer of tissue that separates the cornea from the aqueous humor.

**Why the Correct Answer is Right**
The correct answer is amyloid. The KF ring is composed of amyloid, a type of proteinaceous deposit that accumulates in the Descemet's membrane due to various underlying conditions. This deposition is often associated with systemic amyloidosis, particularly primary amyloidosis (AL amyloidosis), but can also be seen in other conditions such as secondary amyloidosis or Fabry disease. The amyloid deposition in the Descemet's membrane leads to a characteristic ring-shaped appearance, which is a hallmark of KF ring.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because, although mucopolysaccharides are involved in certain corneal dystrophies, they are not the primary component of the KF ring.

**Option B:** This option is incorrect because, although iron deposition is a feature of certain corneal conditions, it is not the primary component of the KF ring.

**Option C:** This option is incorrect because, although calcium deposits are a feature of certain corneal conditions, they are not the primary component of the KF ring.

**Clinical Pearl / High-Yield Fact**
KF ring is a key diagnostic feature of systemic amyloidosis, particularly primary amyloidosis (AL amyloidosis). It is essential to consider the systemic implications of this finding and to investigate for underlying conditions that may be contributing to the amyloid deposition.

**Correct Answer:** C. Amyloid.