Purpose: The aim of the study was to visualize and to quantify pathological foveal avascular zone (FAZ) alterations through optical coherence tomography angiography (OCT-A) in eyes with retinal vein occlusion (RVO) in comparison to the unaffected fellow eyes. Procedures: OCT-A was conducted with the Avanti® RTVue 100 XR system (Optovue Inc., Fremont, Calif., USA). The borders of the superficial vascular layer (SVL) were defined as 3 $μ$m below the internal limiting membrane and 15 $μ$m below the inner plexiform layer, and for the deep vascular layer (DVL) as 15 and 70 $μ$m below the inner plexiform layer, respectively. The length of the horizontal, vertical and maximum FAZ was manually measured for the SVL and DVL in each eye. Additionally, the angle between the maximum FAZ diameter and the papillomacular plane was measured. Results: OCT-A depicted defects within the perifoveal vasculature in eyes with branch retinal vein occlusion (BRVO; n = 11) and central retinal vein occlusion (CRVO; n = 8). These resulted in an enlargement of the maximum FAZ diameter in eyes with RVO (n = 19) in comparison to the healthy fellow eyes (n = 19; 921 $±$ 213 vs. 724 $±$ 145 µm; p = 0.008). Furthermore, a significant correlation was found between best-corrected visual acuity (BCVA) and the maximum FAZ diameter in the DVL (Spearman’s $h̊o$ = -0.423, p