Another cause of painless vision loss is a central retinal vein occlusion (CRVO). This vision loss may be mild to profound and is often due to macular edema. The onset of a CRVO is usually rapid. Ophthalmic examination will reveal retinal hemorrhages and cotton-wool spots. The findings of severe vision loss or an afferent pupillary defect indicate a greater risk for the ischemic type of CRVO, which carries a poor prognosis and is more highly associated with rubeotic glaucoma. Fifty percent of patients who have a CRVO have open-angle glaucoma and/or systemic hypertension. A systemic workup in patients with a CRVO should include measurement of blood pressure and exclusion of other vasculopathic risk factors. Blood workup to rule out coagulopathies (including Factor V deficiency), hyperlipidemia, collagen vascular diseases, and paraneoplastic syndromes may be considered.