PROS1 and acquired polycythemia vera: Although CRVO can be triggered by any state that causes a hypercoagulable local environment (such as by select blood dyscrasias including polycythemia vera, multiple myeloma, Waldenstrom macroglobulinemia, or clotting disorders like factor V Leiden disease, antiphospholipid syndrome, and mutations in antithrombin III and protein S or protein C), the exact pathogenesis remains elusive.