Since the child is having a very large retinoblastoma filling more than half the globe the treatment of choice is enucleation. Eyeball is enucleated along with maximum length of the optic nerve without perforating the eyeball. Enucleation is indicated in the treatment of retinoblastoma when the tumor involves more than half the retina, optic nerve is involved and when glaucoma is present and anterior chamber is involved. Ref: Comprehensive Ophthalmology By AK Khurana, 4th Edition, Page 283.