a. Name four possible diagnosis.

Answer
Retinoblastoma.
Toxocara.
Persistent hyperplastic primary vitreous.
Coat's disease.
The patient has a right leukocoria.

b. Examination of the eye under anaesthesia showed an unifocal lesion as
    above.
    Name five typical histological features which may be seen in this 
    condition.

AnswerFlexner-Wintersteiner rosettes.
Fleurettes.
Homer-Wright rosettes.
Necrosis.
Calcification.

The picture shows a white dome-shaped lesion typical of 
retinoblastoma. Flexner-Wintersteiner rosettes consist of cuboidal cells circled around a central lumen. Homer Wright rosettes may also be seen but they are not specific for retinoblastoma and can occur in neuroblastoma or medulloepithelioma, unlike 
Flexner-Winsteiner rosettes they have not central lumen instead the centre of the rosettes are filed by neurofibrillary tangles. Fleurettes are also seen which are flower-like grouping of tumor 
cells which look like photoreceptors and are a marker of well-differentiated retinoblastoma. Calcifiction is common as is necrosis because the tumour rapidly outgrows its blood supply.

Answer1%. 
In a child with unifocal lesion as in this case without a family history. The risk of the parents' second child's developing 
retinoblastoma is about 1% if the first child had unifocal disease and about 6% if the first child had retinoblastoma in both eye.

d. Enucleation was carried out in this patient. Name 2 features in the 
    enucleated specimen which are assocaited with poor prognosis.

Answer
Optic nerve invasion.
Choroidal invasion.
Extrascleral invasion.

Answer
The risk is less. 
In unilateral retinoblastoma without family history, the child inherits two normal allelic suppressor genes. Two mutations appear in the retina leading to retinoblastoma in one eye. Otherwise, the patient is at risk of osteosarcoma and cutaneous melanoma.