Objective:To investigate the alteration of retinal perfusion in aquaporin-4 antibody (AQP4-ab) positive neuromyelitis optica spectrum disorders (NMOSD) patients by optical coherence tomography angiography (OCTA).Methods:A case-control study. Forty-eight AQP4-ab positive NMOSD patients (96 eyes) and 20 age and gender matched healthy controls (40 eyes) were recruited from September 2015 to August 2017 at the Eye & ENT Hospital of Fudan University. Patients of both eyes were included in the groups. The patients were further divided into 4 subgroups (0 ON, 1 ON, 2 ON, 3+ ON group) according to the number of episodes of ON (0, 1, 2, or 3+) with respect to 30、22、31、13 eyes. 0 ON group had no history of ON episodes; 1 ON group, 2 ON group, and 3+ ON group had ON episodes 1, 2, ≥3 times, respectively. All patients underwent complete ophthalmological examinations including BCVA, visual field and OCTA examination. The BCVA was recorded for each eye using metric notation from the Snellen chart, and then converted to the logarithm of the minimum angle of resolution. The central visual field was assessed using a Humphrey Field Analyzer 750 and the mean deviation (MD) was determined. OCTA scans of the optic disc (4.5 mm × 4.5 mm) and macula (6 mm × 6 mm) were acquired. Radial peripapillary capillary (RPC) vessel density, superficial capillary plexus vessel density (SVD), the thickness of ganglion cell and inner plexiform layer (GCIPL) and peripapillary retinal nerve fiber layer (pRNFL) were determined. The generalized estimating equations was performed to compare the difference of BCVA, MD, pRNFL thickness, GCIPL thickness, RPC vessel density and SVD among the groups and the correlations between retinal perfusion and retinal structure, visual function were analyzed.Results:The RPC vessel density and SVD were significant lower in the 0 ON group compared with healthy group (Wald χ2=7.190, 10.134; P<0.01), however, the BCVA, pRNFL and GCIPL thickness were not significant difference between the two groups (Wald χ2=2.308, 1.020, 2.558; P>0.05). The BCVA, visual field MD, RPC vessel density, SVD, pRNFL and GCIPL were significant lower in 1 ON, 2 ON and 3+ ON groups compared with healthy group and 0 ON group (Wald χ2=12.390, 11.346, 38.860, 18.040, 45.418, 26.608; P<0.001 ), but the parameters had no significant difference among the three groups ( P>0.05). The RPC vessel density was significantly correlated with pRNFL thickness ( β=0.372, standard error=0.018, P<0.001), and the SVD was significantly correlated with GCIPL thickness ( β=0.115, standard error=0.204, P<0.001). The MD and BCVA was significantly correlated with peripapillary vessel density after adjustment for other variables (BCVA: β=0.025, standard error=0.005, P=0.000; visual field MD: β=0.737, standard error=0.185, P=0.000). Conclusions:Subclinical primary retinal vasculopathy may occur in NMOSD prior to ON attack, the ON attack may further impair visual function, retinal structure and perfusion, however, the extent of injure is not relevant with the increase of ON attack. The peripapillary vessel density might be a sensitive predictor of visual outcomes in NMOSD patients.