A 62-year-old woman from Mumbai with a 5-year history of primary open-angle glaucoma presents for follow-up. She has been on latanoprost monotherapy for 3 years with good adherence. Current IOP is 18 mmHg in both eyes on applanation tonometry. However, automated perimetry performed 6 months ago showed a new superior arcuate defect in the left eye, and repeat testing today confirms progression of the defect with a mean deviation (MD) decline of 2.5 dB. Optic disc photography shows progressive inferotemporal notching in the left eye. The patient reports no adverse effects from latanoprost. What is the most appropriate next step?