**Core Concept**
The question is testing the understanding of the refractive powers of the eye, specifically the maximum refraction that occurs in the eye. The eye's refractive power is primarily attributed to the cornea and the lens. The cornea is responsible for the majority of the eye's refractive power due to its large curvature and refractive index.

**Why the Correct Answer is Right**
The correct answer is the part of the eye responsible for the majority of the eye's refractive power. The cornea's refractive index is approximately 1.376, and its curvature is responsible for a significant portion of the eye's total refractive power. The cornea's refractive power can be estimated using the power of the cornea formula: P = (n-1) x 100, where n is the refractive index of the cornea.

**Why Each Wrong Option is Incorrect**
* **Option A:** The lens is responsible for accommodation and variable refraction, but it is not the part of the eye responsible for the maximum refraction.
* **Option B:** The vitreous humor is a transparent gel-like substance that fills the space between the lens and the retina, but it does not contribute significantly to the eye's refractive power.
* **Option D:** The retina is the light-sensitive tissue at the back of the eye, but it is not responsible for refraction.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the cornea is responsible for the majority of the eye's refractive power, and its irregularities can lead to refractive errors such as astigmatism.

**Correct Answer: C. Cornea. The cornea is responsible for the majority of the eye's refractive power.**