**Core Concept**
The lens in the eye contains specific antigens that trigger an immune response in certain individuals. This is a crucial concept in ophthalmology, particularly in the context of autoimmune diseases.

**Why the Correct Answer is Right**
The correct answer is related to the presence of specific proteins in the lens that can stimulate an immune response. The lens contains proteins such as alpha-crystallin, beta-crystallin, and gamma-crystallin, but the key antigen is the S-antigen, also known as interphotoreceptor retinoid-binding protein (IRBP). This protein is recognized by the immune system as foreign, leading to the development of autoimmune disorders such as sympathetic ophthalmia and Vogt-Koyanagi-Harada syndrome.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the correct antigen present in the lens. While the lens does contain various proteins, not all of them are recognized as antigens by the immune system.
* **Option B:** This option is incorrect because it is not related to the lens or its antigens. This distractor is trying to mislead the reader by introducing a concept unrelated to the question.
* **Option C:** This option is incorrect because it is a type of protein found in the lens, but it is not the specific antigen that triggers an immune response.

**Clinical Pearl / High-Yield Fact**
The S-antigen, or IRBP, is a key antigen in the development of autoimmune disorders affecting the eye. It is essential for medical students to remember this concept to understand the pathophysiology of these conditions.

**Correct Answer: C. S-antigen**