Background and purpose <p>To describe a rare case of combined medial long posterior ciliary occlusion associated with nasal hemiretinal ischemia due to atherosclerotic disease and to outline the possible hemodynamic mechanisms that can explain this association.</p> Case presentation <p>A 65-year-old female patient presented with iris neovascularization with angiographic evidence of watershed choroidal infarction in the setting of non-filling of the nasal choroid and the nasal half of the optic disc on fluorescein and indocyanine green angiography associated with superior and inferior amalric triangular infarcts. The nasal retinal arteries and veins showed significant filling delays. An extensive work-up was carried out, including neurovascular imaging, which was unremarkable except for the known atherosclerotic disease.</p> Conclusions and importance <p>The best explanation for this appearance is a sectoral hemodynamic failure across the standard watershed zone between the medial posterior ciliary artery (MPCA) and the nasal branches of the central retinal artery (CRA). MPCA obstruction most likely produced nasal choroidal and optic-disc ischemia, as well as subsequent hypoperfusion of adjacent nasal CRA branches. Recognizing this pattern emphasizes the intricate interconnectedness of the retinal and choroidal circulations and precludes misdiagnosis as abnormal CRA or venous blockage.</p>