**Core Concept**
Retinoblastoma is a malignant tumor of the retina, primarily affecting young children. It is characterized by the uncontrolled proliferation of immature retinal cells, often leading to vision loss and potentially life-threatening complications.

**Why the Correct Answer is Right**
Retinoblastoma is the most common primary intraocular tumor in childhood, accounting for approximately 40% of all eye tumors in this age group. The tumor arises from the embryonal cells of the retina, which are sensitive to mutations in the RB1 gene. Mutations in this gene can lead to the loss of cell cycle regulation, resulting in uncontrolled cell growth. The characteristic "cat's eye" reflex, a bright white reflection in the pupil, is often seen in cases of retinoblastoma due to the accumulation of calcium in the tumor cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Neurofibromatosis is a genetic disorder characterized by the growth of nerve tissue tumors, but it is not a primary intraocular tumor. While it can cause optic gliomas, which affect the optic nerve, it is not the most common primary intraocular tumor in childhood.
**Option C:** Cavernous haemangioma is a benign vascular tumor that can occur in the eye, but it is not the most common primary intraocular tumor in childhood. It is typically seen in adults and is not associated with the characteristic "cat's eye" reflex.
**Option D:** Melanotic melanoma is a type of cancer that affects the pigment cells of the eye, but it is rare in children and is more common in adults.

**Clinical Pearl / High-Yield Fact**
Retinoblastoma is often associated with a family history of the disease, and genetic counseling is essential for families with a history of this tumor. The "cat's eye" reflex is a critical diagnostic clue, and prompt recognition is essential for early treatment and improved outcomes.

**✓ Correct Answer: B. Retinoblastoma**