You are called to see a 63 year old hypertensive, type II diabetic male, who complains that he has been progressively losing vision in his left eye (OS) over the past 2 days.  His visual loss is completely painless.

On examination his visual acuity is 20/20 OD and 20/200 OS (pinhole).   Funduscopy appeared normal OD, but had the following appearance OS: