A 52-year-old man with chronic hypertension presents with gradual bilateral blurring of vision over 3 weeks. He denies pain or diplopia. Fundoscopy shows bilateral disc swelling with obscured margins, retinal haemorrhages, cotton-wool spots, and hard exudates in a star pattern around the macula. Intraocular pressure is 18 mmHg bilaterally. Visual acuity is 6/9 in both eyes. What is the most appropriate immediate next step?