**Core Concept**
Keratoconus is a progressive, non-inflammatory eye disease characterized by thinning and conical protrusion of the cornea, leading to irregular astigmatism and vision loss. It is a complex condition involving structural and biomechanical changes in the cornea.

**Why the Correct Answer is Right**
Keratoconus is typically defined by the presence of conical corneal protrusion, often with a characteristic "cone-shaped" appearance on anterior segment imaging studies. This is often associated with thinning and ectasia of the corneal tissue, which can lead to significant visual impairment. The pathophysiology of keratoconus is multifactorial, involving both genetic and environmental factors that contribute to the weakening of the cornea.

**Why Each Wrong Option is Incorrect**
**Option A:** This option may refer to a different definition of keratoconus, but it is not the accepted definition.
**Option B:** This option may refer to a different condition, such as Fuchs' endothelial dystrophy or corneal dystrophy, which are distinct from keratoconus.
**Option C:** This option may refer to a different characteristic of keratoconus, but it is not the primary defining feature.

**Clinical Pearl / High-Yield Fact**
Keratoconus is often associated with a history of eye rubbing, which can exacerbate the condition. Patients with keratoconus should be advised to avoid eye rubbing and wear protective eyewear to minimize further corneal damage.

**Correct Answer: C.** Keratoconus is a progressive, non-inflammatory eye disease characterized by thinning and conical protrusion of the cornea.