Retinal vein occlusion is a common retinal vascular disease and cause of visual loss. Depending on the location of obstruction, it can be classified into central retinal vein occlusion (CRVO), branch retinal vein occlusion (BRVO) and hemi-retinal vein occlusion (HRVO). The condition is labelled as CRVO if the blockage of central retinal vein takes place at the lamina cribrosa. Based on the area of capillary non-perfusion, CRVO can be sub-divided into ischaemic and non-ischaemic types. Ischaemic CRVO is defined by the Central Retinal Vein Occlusion Study (CVOS) as CRVO with fluorescein angiographic evidence of >10 disc areas of capillary nonperfusion on seven-field fundus fluorescein angiography.