A 52-year-old woman from Mumbai presents with a 2-month history of progressive visual field loss. She reports seeing a dark shadow starting from the periphery of her left eye that is gradually advancing toward the center. On examination, visual acuity is 6/9 in both eyes. Fundoscopy shows a pale, elevated optic disc with blurred margins in the left eye, and the right optic disc appears normal. Humphrey visual field testing of the left eye reveals an expanding peripheral scotoma with a nasal step pattern. Intraocular pressure is 16 mmHg in both eyes. What is the most appropriate next step in management?