**Core Concept**
The patient's symptoms suggest an autoimmune response triggered by an environmental factor, leading to inflammation in multiple joints and the eyes. This condition is characterized by the deposition of immune complexes in various tissues, including synovial membranes and the conjunctiva.

**Why the Correct Answer is Right**
The patient's symptoms are most consistent with **Reiter's Syndrome**, also known as Reactive Arthritis. This condition typically occurs after an infection, such as gastrointestinal or genitourinary, and is associated with the formation of immune complexes. The gritty pain in the eye is due to conjunctivitis, while the joint pain is caused by inflammation of the synovial membranes. The HLA-B27 antigen is a significant risk factor for developing this condition.

**Why Each Wrong Option is Incorrect**
- **Option A:** This option is likely a distractor, but it doesn't specify the correct condition.
- **Option B:** **Vernal Keratoconjunctivitis** is a seasonal allergic eye condition, which doesn't explain the joint pain.
- **Option C:** **Acute Conjunctivitis** is an inflammation of the conjunctiva, but it doesn't account for the joint pain.
- **Option D:** **Sjögren's Syndrome** is an autoimmune disorder characterized by dry eyes and dry mouth, but it doesn't typically cause joint pain.

**Clinical Pearl / High-Yield Fact**
Reiter's Syndrome is a classic example of a seronegative spondyloarthropathy, characterized by the absence of rheumatoid factor and the presence of HLA-B27 antigen.

**Correct Answer:** C.