Arteritic Anterior Ischemic Optic Neuropathy (Giant Cell Arteritis)

A 76-year-old woman presents with sudden complete vision loss in the right eye preceded by three weeks of new bitemporal headache, scalp tenderness, and jaw claudication. On fundoscopy, the structure marked **A** is noted—a chalky-white pallid swollen optic disc with blurred margins. ESR is 98 mm/hr and CRP is 78 mg/L. Temporal artery biopsy confirms granulomatous inflammation with giant cells. Which of the following best explains the pathophysiology of the optic disc appearance marked **A** in this patient?