A 58-year-old man presents to the ophthalmology clinic with a 3-week history of progressive blurred vision and eye pain. On examination, his right pupil is 6 mm and reacts sluggishly to light, while the left pupil is 3 mm and reacts briskly. When a torch is swung from the left eye to the right eye (swinging flashlight test), the right pupil dilates paradoxically. Visual acuity in the right eye is 6/60 and in the left eye is 6/6. Fundoscopy reveals optic disc swelling and retinal hemorrhages in the right eye. What is the most likely diagnosis?