A 52-year-old man with type 2 diabetes mellitus (HbA1c 9.2%) presents with gradual blurring of central vision and difficulty reading over the past 3 months. Fundoscopy reveals the circinate hard exudate ring marked **A** in the diagram, threatening the fovea with adjacent retinal thickening. OCT confirms central macular involvement with intraretinal cystoid spaces and central thickness of 420 microns. Which of the following best explains the pathophysiology underlying the formation of the hard exudates marked **A**?