A 42-year-old woman from Mumbai presents with sudden onset of a 'shadow' or 'curtain' in her right eye that started superiorly and progressed downward over 2 hours. She denies pain. Visual acuity is 6/9 OD. Fundoscopy reveals a dark, elevated shadow in the superior retina with a clear demarcation line. The optic nerve appears normal. Which retinal layer is compromised, and what is the primary vascular pathology?