Macular edema secondary to occlusion of the retinal veins.

Occlusion of the central and branch retinal veins causes macular edema by provoking increased venous pressure which is transmitted to the perifoveal capillaries. Damage to the perifoveal capillary endothelium results in leakage with macular edema. The severity of the retinal findings (i.e., macular hemorrhages, macular edema, etc.) is determined by the location, completeness, duration, and evolution of the obstruction (i.e., recanalization of a thrombus). Spontaneous remission of macular edema secondary to either a partial central or branch occlusion carries a relative good visual prognosis. Chronic macular edema secondary to occlusion of either central or branch veins is associated with a relatively poor visual prognosis. In selected cases, paramacular photocoagulation can reverse chronic macular edema and result in visual improvement.