**Core Concept**
Leucocoria, or white pupillary reflex, is a sign of retinoblastoma in children. Retinoblastoma is a malignant tumor of the retina, and large tumors can cause a large globe due to secondary glaucoma and increased intraocular pressure.

**Why the Correct Answer is Right**
The treatment of choice for large retinoblastoma with a large globe is enucleation, which involves surgical removal of the affected eye. This approach is necessary to prevent the tumor from spreading and to alleviate symptoms such as pain and vision loss. Enucleation also provides a specimen for histopathological examination, which helps in confirming the diagnosis and determining the extent of the tumor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because chemotherapy is typically used as an adjunctive treatment for retinoblastoma, especially in cases where the tumor is small or has not spread. However, it is not the primary treatment for large retinoblastoma with a large globe.

**Option B:** This option is incorrect because photocoagulation is a treatment for retinal tears or diabetic retinopathy, not for large retinoblastoma with a large globe.

**Option C:** This option is incorrect because radiation therapy is not the first line of treatment for large retinoblastoma with a large globe, especially in young children. Radiation can have long-term side effects, such as cataracts and secondary tumors.

**Clinical Pearl / High-Yield Fact**
Early detection and treatment of retinoblastoma are crucial, as it can spread to the optic nerve and central nervous system if left untreated. Leucocoria is a classic sign of retinoblastoma, and any child presenting with this symptom should undergo a thorough ophthalmological evaluation.

**Correct Answer: D. Enucleation of the affected eye.**