A 62-year-old woman with poorly controlled diabetes mellitus presents with progressive visual loss over 3 months. She denies floaters or photopsia. Examination reveals visual acuity of 6/60 in both eyes. Fundoscopy shows extensive retinal neovascularization, vitreous haemorrhage, and a smooth, funnel-shaped retinal detachment with the apex at the optic disc and the base at the equator. There are no visible retinal breaks. What is the most appropriate next step in management?