Branching characteristics. Confocal Z-series images were compressed and counted “blindly” for number of vessel branch points per image. C57BL/6.gfp retinas averaged 17.8 branches per image (n=5). iNOS.gfp retinas averaged 48 branch points per image (n=4). eNOS.gfp retinas averaged 0.29 branch points per image (n=38). The blood vessels of iNOS^–/– retinas were 2.7 times more branched than WT animals (P < .0001), whereas eNOS^–/– retinas were 61.5 times less branched than WT (P < .0002). Error bars indicate standard errors of the means.