A 79yo woman presented with visual loss in the left eye of one day's duration. She described the visual loss as sudden, mostly central, and painless. Her past medical history was significant for hypertension. On examination, the vision was 20/20 OD and counting fingers OS. There was a left relative afferent pupillary defect. Her extraocular motility was full. The Goldmann visual field is shown in Fig. 1.

Q: Is there a reliable way to differentiate sudden visual loss from sudden discovery of visual loss?