A 58-year-old man from Delhi presents with gradual, painless vision loss over 2 years. On examination, intraocular pressure (IOP) is 28 mmHg in both eyes, optic disc shows 0.7 cup-to-disc ratio with inferior notching, and visual fields show early superior arcuate defects. Gonioscopy confirms open angles. He has no prior ocular history and is treatment-naïve. What is the most appropriate next step in management?