**Core Concept**
The refractive index is a critical factor in determining the eye's ability to focus light. It is the ratio of the speed of light in a vacuum to the speed of light in a given medium. In the context of the eye, the refractive index varies between different components, with some having higher refractive indices than others.

**Why the Correct Answer is Right**
The lens of the eye has the maximum refractive index among its components. This is due to the high concentration of proteins and other substances that contribute to its refractive index. The lens is composed of a high percentage of water and proteins, such as crystallin, which give it a high refractive index. This allows the lens to bend light significantly and focus it on the retina.

**Why Each Wrong Option is Incorrect**
**Option A:** The cornea, although having a high refractive index, is not the component with the maximum refractive index. It has a refractive index of approximately 1.376, which is lower than that of the lens.

**Option B:** The sclera, which provides structural support to the eye, has a relatively low refractive index, making it an unlikely candidate for the correct answer.

**Option C:** The retina, which is responsible for converting light into electrical signals, has a refractive index similar to that of water and is not the component with the maximum refractive index.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the lens is responsible for changing its refractive index to accommodate for near and far vision, a process known as accommodation. This is achieved through the ciliary muscles, which change the shape of the lens to adjust its refractive power.

**Correct Answer: C. Lens**