Imaging modalities in retinal vein occlusion
Retinal vein occlusion (RVO) is the second most common visionthreatening retinal vascular disorder after diabetic retinopathy. The primary types of RVO are branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO), with hemiretinal vein occlusion (HRVO) considered a subtype of either BRVO or CRVO. Both BRVO and CRVO are further broken down into ischemic and non-ischemic types, and imaging studies can be helpful in diagnosing and classifying the type and perfusion status of RVO and the presence or absence of perfused cystoid macular edema (CME). Fundus photography in any acute RVO may show flame-shaped or dotblot hemorrhages, cotton-wool spots, and dilated tortuous veins. These findings will usually occur in one quadrant for BRVO, two quadrants for HRVO, and all four quadrants for CRVO. In all RVOs, optic disc edema and CME are commonly seen, and in ischemic RVO, the intraretinal hemorrhage can be extensive leading to the classic blood-and-thunder appearance. The two subtypes of BRVO are dictated by perfusion status and determination of the presence or absence of ischemic CME, as visualized on fluorescein angiography (FA). Other FA findings may include delayed filling of the occluded retinal vein, vessel tortuosity, and blockage or leakage from intraretinal hemorrhage, and later collateral vessel formation. However, these findings are not specific to BRVO and may also be seen in HRVO and CRVO in the affected distribution. Optical coherence tomography (OCT) can help detect the amount and extent of CME. The subtypes of CRVO are ischemic, non-ischemic, and indeterminate, and perfusion classification relies on the amount of retinal non-perfusion seen on FA. Other FA findings include delayed filling of the occluded retinal vein, blockage from hemorrhage, and leakage from the optic disc or parafoveal capillaries. On optical coherence tomography angiography (OCTA), CRVO can demonstrate CME in the superficial capillary plexus (SCP), and in ischemic CRVO, there can be an obvious loss of capillaries in SCP; however, the use of OCTA to determine perfusion status of CRVO is not yet common practice.
