Christina J Flaxel, MD Retinal vein occlusions are the next most common sight-threatening vascular disorder after DR. Central retinal vein occlusions (CRVO) and branch retinal vein occlusions (BRVO) are etiologically and funduscopically distinct from DR, but may occur more frequently in patients with diabetes than patients without the disease. CRVO and BRVO are managed differently than DR, so accurate differential diagnosis of these entities is especially important in patients with diabetes. CRVO and BRVO are caused by thrombosis in a blood vessel with a narrowed lumen. The risk of CRVO increases with systemic hypertension, diabetes, and open-angle glaucoma. Physical activity decreases the risk of CRVO. BRVO is also associated with hypertension and diabetes. Current smoking has been identified as an additional risk factor for BRVO, but unlike CRVO, there is no association with cardiovascular disease. Furthermore, BRVO is not associated with elevated blood lipid levels. While diabetes is a risk factor for the development of retinal vein occlusions, the classical retinal lesions produced by these disorders have a markedly different appearance than DR on funduscopy. CRVO and BRVO may create a distinctive pattern of numerous hemorrhages scattered distal to the location of the thrombosis. CRVO may have either of 2 distinctive patterns. The first is nonischemic or perfused CRVO, the second is ischemic or hemorrhagic or nonperfused CRVO. Nonischemic CRVO manifests with mild dilation and tortuosity of the central retinal vein with hemorrhages in all 4 quadrants of the retina; ischemic CRVO manifests with marked venous dilation and tortuosity, extensive 4-quadrant hemorrhages, and many cotton-wool spots. The classic appearance of CRVO is sometimes referred to as a “tie-dyed” retina. BRVO is associated with arteriovenous nicking and focal arteriolar narrowing. BRVO is 3 times as common as CRVO, and is further characterized by superficial hemorrhages, retinal edema, and cotton-wool spots in the sector of the retina drained by the affected vein. Outcomes data for retinal vein occlusions are based on data gathered from patients with BRVO. The clinical course of BRVO is relatively stable. About 50%-60% of patients with BRVO maintain visual acuity of 20/40 or better after 1 year. The visual prognosis is related to the extent of capillary damage and retinal ischemia. Hemorrhages and edema may resolve over time, with capillary compensation and collateral formation permitting restitution of blood flow, and improved visual function. On the other hand, vision may be reduced in acute cases from macular edema, retinal hemorrhage, or perifoveal retinal capillary occlusion or progressive capillary closure. Permanent vision loss may occur due to macular ischemia, macular edema, lipid exudates, pigment disturbance, subretinal fibrosis, or epiretinal membrane formation. Nonischemic CRVO may be asymptomatic, but ischemic CRVO is characterized by extensive 4-quadrant hemorrhages. Transiently obscured vision may occur prior to the development of CRVO. Nonischemic CRVO has a more favorable prognosis than ischemic CRVO. About 50% of cases of nonischemic CRVO resolve spontaneously, and 30% partially resolve, but 20% will convert to ischemic CRVO. Only 10% of patients with ischemic CRVO obtain a post-treatment visual acuity of 20/400 or better. FA is used to evaluate both macular and peripheral ischemia when the hemorrhage has cleared enough to permit it. OCT could be done earlier, but would not change treatment timing, since laser or other treatments would not be considered until the hemorrhage has cleared enough to determine the level of ischemia. Color fundus photos are recommended for CRVO. In eyes with chronic macular edema and intact perifoveal retinal capillary perfusion, wait 3 months before performing laser in case spontaneous resolution occurs. Eyes with macular ischemia should not be treated, but eyes with significant peripheral ischemia (≥5 disc diameters) or iris neovascularization may benefit from PRP. Generally, treating macular edema with grid laser is not beneficial, but younger patients show a trend toward better results with this treatment than do older patients. Corticosteroid therapies and the anti-VEGF agent pegaptanib are under investigation as potential treatments for macular edema secondary to CRVO or BRVO. Surgical and pharmacological thrombolytic procedures have also been proposed for CRVO and BRVO, but no long-term randomized controlled clinical trials for these interventions have been performed. |
