A 58-year-old man presents with blurred vision in his left eye for 1 month. He was diagnosed with type 2 diabetes mellitus 8 years ago, and is currently on oral metformin and glimepiride. His medical history is otherwise unremarkable. His last ophthalmological evaluation was 2 years ago, at which time mild non-proliferative diabetic retinopathy without clinically significant macular edema was noted.