## **Core Concept**
Retinoblastoma is a malignant tumor of the retina, primarily affecting children. Enucleation is a surgical procedure often performed for advanced cases. After enucleation, examining specific tissues for metastasis is crucial for determining the extent of disease spread.

## **Why the Correct Answer is Right**
The correct answer involves identifying the tissue that is most likely to be sectioned to detect systemic metastasis in retinoblastoma. In cases of enucleation for retinoblastoma, the **optic nerve** is a common pathway for the spread of tumor cells to the brain and, subsequently, to other parts of the body. Therefore, sectioning the optic nerve is critical for assessing the risk of systemic metastasis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although the sclera is a part of the eye, it is not the primary tissue examined for systemic metastasis in retinoblastoma.
- **Option B:** This option might seem plausible but is not the correct answer because, while the choroid can be involved in advanced disease, it is not the primary tissue sectioned to assess for systemic metastasis post-enucleation.
- **Option C:** This option is incorrect because, although the extraocular muscles can be involved in advanced orbital disease, they are not primarily sectioned for assessing systemic metastasis.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **optic nerve** is a critical structure to examine for tumor invasion, as its involvement significantly affects the prognosis and management of retinoblastoma, including the risk of central nervous system (CNS) spread.

## **Correct Answer:** . Optic nerve.