Okay, let's tackle this question. The patient is a 5-year-old boy with leucocoria in the right eye diagnosed as diffuse retinoblastoma involving the entire globe. The left eye has a small tumor in the periphery. The question is about the ideal management.

First, I need to recall the management of retinoblastoma. Retinoblastoma is a pediatric eye tumor, typically under 5 years old. Management depends on the stage and extent of the tumor. For unilateral disease, if the tumor is large and involves the entire globe, enucleation is often the treatment. But if the other eye has a small tumor, maybe they can preserve vision with other treatments like chemotherapy, laser, or cryotherapy.

In this case, the right eye has diffuse involvement, so enucleation is likely needed. The left eye has a small tumor, so maybe conservative treatment is possible. The options would probably include enucleation of the right eye and treatment of the left eye. The correct answer would be the combination of enucleation for the right and local treatment for the left.

The wrong options might include unnecessary enucleation of both eyes, which would be incorrect because the left eye has a small tumor. Alternatively, maybe they suggest only chemotherapy without enucleation, but if the globe is involved entirely, enucleation is necessary. Another wrong option could be radiation therapy, which is less commonly used now due to risk of secondary tumors.

So the correct answer would be enucleation of the right eye and focal therapy for the left. The clinical pearl here is that enucleation is the mainstay for diffuse involvement, while salvage therapy is used for smaller tumors to preserve vision.

**Core Concept**
Retinoblastoma management depends on tumor size, laterality, and globe involvement. Enucleation is indicated for diffuse intraocular disease to prevent metastasis, while focal therapies preserve vision in smaller tumors.

**Why the Correct Answer is Right**
The right eye has *diffuse retinoblastoma involving the entire globe*, making enucleation the standard treatment to eliminate tumor burden and prevent systemic spread. The left eye’s small peripheral tumor (2-3 mm) is amenable to *focal therapies* like laser photocoagulation, cryotherapy, or plaque brachytherapy to preserve vision and avoid unnecessary enucleation.

**Why Each Wrong Option is Incorrect**
**Option A:** Enucleation of both eyes is unnecessary if the left eye’s tumor is treatable with focal therapy.
**Option B:** Chemotherapy alone for the right eye is ineffective for diffuse intraocular disease; enucleation remains the only curative option.
**Option C:** Radiation therapy is contraindicated in children due to high risk of secondary malignancies and retinal dysplasia.

**Clinical Pearl / High-Yield Fact**
**Enucleation is mandatory for diffuse retinoblastoma** to prevent orbital and systemic metastasis. For unilateral disease with small contralateral tumors, *salvage therapy* (laser, cryotherapy) is preferred to retain vision. Always prioritize globe preservation in the second eye if feasible.

**Correct Answer: C. Enucleation of the right eye and focal therapy for the left eye**

✓ Correct Answer: C. Enucleation of right eye and focal therapy of the left eye