Backfilling of Nonperfused Retina from an Adjacent Sector in Branch Retinal Artery Occlusion
A 63 year old woman with hypertension was seen with acute, painless visual loss of the left eye from a branch retinal artery occlusion. A - Monochromatic fundus photograph of the left eye showing ischemic retinal whitening that is present in the sector of retina off the disk from 12 to 3 o'clock. The ischemic zone abuts the fovea. B - Frame from the arteriovenous phase of the fluorescein angiogram shows absence of perfusion of the superotemporal retina because of the obstructed superotemporal branch retinal artery. Yellow arrows denote two intrinsic anastomotic veins that connect the inferotemporal quadrant circulation with the veins of the superotemporal quadrant. Some backfilling of the superotemporal veins has begun. C - A frame from a later stage of the arteriovenous phase of the fluorescein angiogram shows that the entire superotemporal branch retinal vein (red arrow) has filled from backflow via the anastomoses with the veins of the inferotemporal quadrant. The green arrow denotes a superotemporal branch retinal arteriole that is backfilling from anastomoses with the inferotemporal microcirculation. The backfilling of the arterioles occurs later than the veins because of a longer path or higher resistance than is the case for the venous backfilling. Venous backfilling has also begun in the nasal macula (turquoise arrow). We can infer that venous anastomoses are hemodynamically less significant across the nasal macular portion of the horizontal raphe than across the temporal macular potion because of the delay in backfilling in the nasal macular region relative to the temporal macular region. D - Frame from the recirculation phase of the fluorescein angiogram shows continuation of the arterial backfilling of the superotemporal quadrant. The flow is so slow that the fluorescein dye in the superotemporal branch retinal artery is pooled over a dependent layer of erythrocytes within the arterial lumen.