**Core Concept**
Keratoconus is a progressive eye disease characterized by thinning of the cornea, leading to a conical shape and vision distortion. The prevention of keratoconus involves the use of rigid gas permeable contact lenses to flatten the cornea and reduce the risk of progression.

**Why the Correct Answer is Right**
The correct answer is **Rigid Gas Permeable (RGP) Contact Lenses**. These lenses are designed to provide mechanical support to the cornea, thereby reducing the risk of further thinning and conical deformation. By flattening the cornea, RGP lenses help to improve vision and slow down the progression of keratoconus. This is achieved through the application of continuous pressure, which helps to strengthen the corneal tissue and reduce the risk of ectasia.

**Why Each Wrong Option is Incorrect**
**Option A:** **Soft Contact Lenses** - These lenses do not provide sufficient mechanical support to the cornea and may even exacerbate keratoconus by causing further thinning and deformation.

**Option B:** **Corneal Cross-Linking** - While this is a treatment for keratoconus, it is not a preventative measure and is typically used to stabilize the cornea after progression has occurred.

**Option C:** **Corneal Transplantation** - This is a surgical procedure used to replace a diseased cornea with a healthy one, but it is not a preventative measure for keratoconus.

**Clinical Pearl / High-Yield Fact**
The use of RGP lenses is a crucial preventative measure for individuals with a high risk of developing keratoconus, such as those with a family history or a history of eye injuries.

**Correct Answer:** C. Corneal Cross-Linking