A 28-year-old Indian male with hemoglobin SC disease presents with floaters and blurred vision. Fundoscopy reveals the structure marked **A** in the diagram—a characteristic fan-shaped neovascular frond at the superotemporal retina at the boundary between perfused and non-perfused retina. Which of the following best explains the pathophysiological mechanism underlying the formation of this structure?

Explanation

## Why "Peripheral capillary non-perfusion triggering VEGF release at the boundary between perfused and non-perfused retina" is right The sea-fan neovascularization marked **A** is the hallmark of Stage III proliferative sickle cell retinopathy (PSR). According to Goldberg's classification and pathophysiology, abnormal hemoglobin polymerization under hypoxic conditions causes red cell sickling and occlusion of small peripheral retinal vessels. This peripheral capillary non-perfusion is the critical trigger for VEGF release, which drives neovascularization specifically at the boundary zone between perfused and non-perfused retina—the exact location where sea fans arise. This mechanism is the cornerstone of PSR pathogenesis and explains why sea fans are found at vascular boundaries rather than in areas of uniform perfusion or uniform non-perfusion. ## Why each distractor is wrong - **Central macular ischemia causing diffuse retinal neovascularization**: While macular involvement can occur in PSR, the sea fan is a peripheral phenomenon arising from peripheral capillary non-perfusion, not central macular ischemia. Central macular disease causes subtle vision loss from capillary dropout, not sea-fan formation. - **Chronic retinal hemorrhage leading to iron deposition and RPE hyperplasia**: This describes the pathogenesis of black sunbursts (RPE hyperplasia at sites of resolved hemorrhage) and iridescent spots (hemosiderin deposits), not sea-fan neovascularization. These are secondary findings, not the primary driver of sea-fan formation. - **Optic disc hypoxia causing generalized vascular leakage and edema**: Optic disc involvement (optic disc edema with hemorrhages, marked **C**) is a separate finding in PSR but does not explain the mechanism of peripheral sea-fan formation. Sea fans arise from peripheral non-perfusion, not disc hypoxia. **High-Yield:** Sea fans form at the **boundary** between perfused and non-perfused retina due to VEGF release triggered by peripheral capillary non-perfusion—this is the pathophysiological cornerstone of Stage III PSR. [cite: Goldberg MF, Classification and pathogenesis of proliferative sickle retinopathy. Am J Ophthalmol 1971]