A 48-year-old woman with chronic hypertension (BP 160/100 mmHg, well-controlled on medication for 3 years) undergoes routine fundoscopy. She has arteriovenous nicking, arteriolar narrowing, and scattered flame hemorrhages but no optic disc swelling. In contrast, her sister with acute hypertensive crisis (BP 210/130 mmHg) presents with the same retinal findings plus papilledema and retinal whitening. Which feature best discriminates chronic hypertensive retinopathy from acute hypertensive retinopathy?