Retinal vein occlusion presents as a sudden painless loss of vision, but it may also present with a history of a gradual decline of vision which may correlate with less severe occlusions. The typical clinical constellation in CRVO includes superficial flame-shaped and deep blot-type retinal hemorrhages from the optic nerve head in all four quadrants of the fundus (“blood and thunder” appearance). Often there is a marked dilated, tortuous retinal venous system in combination with optic nerve head swelling. Cotton-wool spots, splinter hemorrhages, and macular edema (ME) are present to varying degrees.

Generally, the described intraretinal hemorrhages are less marked in BRVO and if the occlusion is perfused or nonischemic and is much more marked if the occlusion is non-perfused or ischemic and associated with retinal capillary non-perfusion. The localization of the venous block determines the hemorrhage distribution. If in BRVO the venous obstruction is at the optic nerve head, two quadrants of the fundus may be involved, whereas if the occlusion is peripheral to the disc, one quadrant or less may be involved with retinal hemorrhages.

The clinical picture of a CRVO may be explained by the occlusion of the main trunk of the central retinal vein; however, the pathophysiology is still not clearly understood. Histopathologic studies of enucleated eyes showed a thrombus occluding the lumen of the central retinal vein at or proximal to the lamina cribrosa (Green et al. 1981). This finding suggests that the anatomic variations at the level of the lamina cribrosa may be an important pathogenic point.

The interruption of venous flow in BRVO eyes almost always occurs at retinal intersections. Histopathologically, the retinal artery and vein share a common adventitial sheath. Especially in BRVO the lumen of the vein may be compressed up to one third at the crossing side (Bandello et al. 1998). This and also the vitreous may play important roles in compression of the susceptible arteriovenous crossing sites as evidenced by studies demonstrating that eyes with decreased axial length and a likelihood of vitreo-macular attachment at the crossing are at increased risk of BRVO. The resulting venous obstruction leads to elevation of venous pressure that may overload the collateral drainage capacity and lead to ME and ischemia by mechanisms that are still under investigation.

The vision loss is mostly caused by ME due to reduced blood perfusion and subsequent retinal hypoxia. The ME may also lead to additional reduction in visual acuity that often exceeds the primary ischemic damage and thus represents an important target for therapeutically intervention.

Treatment strategies for ME comprise focal laser photocoagulation (The Branch Vein Occlusion Study Group 1984; Central Retinal Vein Occlusion Study Group 1993; Klein and Finkelstein 1989), intravitreal steroids (Jonas et al. 2005), surgical procedures (Berker and Batman 2008), and, most recently, injection of anti-vascular endothelial derived growth factor protein (VEGF) compounds (Costa et al. 2007; Priglinger et al. 2007).

At the time of initial presentation, a careful assessment of both eyes, including abnormal VA, iris stromal vessels, pupillary reaction, intraocular pressure, as well as history of the duration and the degree of the retinal ischemia, will determine treatment options and an individualized follow-up schedule. Fluorescein and ICG angiography could be useful for the evaluation of treatment options.

Spectral domain OCT (SD-OCT) offers new insight into retinal structures and their alterations especially regarding the integrity of the retinal layers in the fovea. So some interesting factors with predictive value were detected for a favorable short-term visual outcome after anti-VEGF treatment for ME secondary to CRVO (Wolf-Schnurrbusch et al. 2011). One important factor is the presence and integrity of the external limiting membrane (ELM) (Fig. 11.1). It is a bad prognostic sign for the short-term recovery of visual acuity of the ELM if the foveal region is “disturbed” and if we were not able to follow the hyper-reflective band of the ELM in the horizontal or in the vertical SD-OCT scans (Fig. 11.2). Patients with ME in whom SD-OCT images demonstrate an intact outer limiting membrane have a better outcome after intravitreal anti-VEGF therapy than patients with severely compromised outer retinal structures. The integrity of the photoreceptor inner segments (IS) and outer segments (OS) and the retinal pigment epithelium (RPE) is easily assessable, as well as the presence of subretinal and intraretinal fluid accumulation.