A 28-year-old woman with a history of tuberculosis (treated 6 months ago) presents with floaters, blurred vision, and mild photopsia in the left eye for 2 weeks. Anterior chamber is quiet. Fundus examination reveals multiple yellow-white granulomatous lesions in the posterior pole with mild vitritis. Fluorescein angiography shows early hyperfluorescence at lesion margins. Visual acuity is 6/12. What is the most appropriate next step in management?