Retinal vein occlusion (RVO) affects more than 16 million adults worldwide. Vein occlusions are the second leading cause of blindness from retinal vascular disease, trailing only diabetic retinopathy. In general, vein occlusions are classified as central retinal vein occlusion (CRVO), hemicentral retinal vein occlusion (HRVO), or branch retinal vein occlusion (BRVO), based on whether the occlusion occurs in the main vein draining the retina or a small branch of the central retinal vein. HRVO is simply a CRVO with a congenital variation of central retinal vein anatomy in which a hemifield of the retina is spared, dependent upon the specific location of thrombus formation. The congenital anatomic variant in HRVO involves persistence of 2 trunks of the central retinal vein. In normal embryonic development, 1 trunk typically disappears. This module reviews the etiology, epidemiology, diagnosis, and workup of RVO, and provides a concise update on the management of RVO via a review of relevant clinical trials.