Foveal avascular zone. A, Scanning electron micrograph of a retinal vascular cast at the fovea, showing the foveal avascular zone (FAZ) and under lying choriocapillaris, the sole source of oxygen to the retina at this location. B, Fluorescein angiogram of the FAZ, obtained during the peak venous phase. Fluorescence from the choriocapillaris is blocked by the RPE.