Ischemic macular edema. Recognition and favorable natural history in branch vein occlusion.

Eyes with macular edema caused by retinal branch vein occlusion underwent masked evaluation of fluorescein angiography to determine complete macular perfusion vs incomplete macular perfusion (capillary dropout, ischemia). Cases evaluated as incomplete macular perfusion showed a greater frequency of improvement (91%) in visual acuity than did perfused cases (29%) (P = .003) after a mean follow-up of 39 months. Ischemic edema is often transient, and is associated with a good outcome in visual acuity (median final visual acuity was 20/30). Perfused macular edema has a poorer prognosis for visual acuity (median final visual acuity was 20/80). Macular ischemia is usually associated with a broken foveal capillary ring. Previous animal research on ischemic brain edema has shown that following brain ischemia, an intracellular and an extracellular hypertonic environment lead to intracellular and extracellular edema (cytotoxic edema), which is often followed by vascular protein leakage (vasogenic edema). A similar occurrence in ischemic retina could explain the transient edema reported herein, with good outcome in visual acuity following the spontaneous resolution of edema.