**Core Concept**
Iris tumors are rare, but can be benign or malignant. The iris is a complex structure composed of smooth muscle, collagen, and melanocytes, making it susceptible to various types of lesions.

**Why the Correct Answer is Right**
Melanocytoma is a true tumor of the iris, characterized by a benign proliferation of melanocytes. It is a distinct entity from melanoma, which is a malignant tumor. Melanocytoma is typically a solitary, pigmented lesion that can be asymptomatic or cause localized symptoms such as glaucoma or vision loss. The exact pathogenesis of melanocytoma is unknown, but it is thought to arise from the clonal proliferation of melanocytes.

**Why Each Wrong Option is Incorrect**
**Option A:** Iris nodules can be caused by inflammation, trauma, or other non-neoplastic processes. They are not true tumors.
**Option B:** Iris heterochromia is a benign condition characterized by a difference in iris color between the two eyes. It is not a tumor.
**Option C:** Iris melanoma is a malignant tumor of the iris, but it is distinct from melanocytoma. Melanoma is a more aggressive condition that requires prompt treatment.

**Clinical Pearl / High-Yield Fact**
Melanocytoma is often confused with melanoma, but they have distinct clinical and histopathological features. A thorough evaluation, including imaging and biopsy, is necessary to differentiate between these two conditions.

**Correct Answer:** C. Iris melanoma is a malignant tumor of the iris, but it is distinct from melanocytoma.