This study characterized and evaluated normal tension glaucoma (NTG) in obstructive sleep apnea syndrome (OSAS).In this retrospective, cross-sectional study, all participants were examined with polysomnography (PSG). Functional parameters of standard automated perimetry (SAP) were recorded. Structural parameters in optical coherence tomography angiography (OCTA) included peripapillary superficial vessel density (VD RPC), peripapillary whole-layer (VD NH), and superficial and deep macular area VD. Participants were categorized into perimetric and nonperimetric groups by SAP result. Low reliability of SAP and signal strength index <50 in OCTA were excluded.Severity of OSAS was graded by apnea-hypopnea index (AHI) in PSG. Those with moderate/severe OSAS (AHI ≥ 15, n = 39) had longer neck circumference and shorter ocular axial length than mild OSAS (AHI < 15, n = 14). Furthermore, there was significantly higher AHI and larger neck circumference in the NTG perimetric group (n = 27) than in the control group (n = 26; p < 0.001 and p = 0.047, respectively). Superficial and deep-layer peripapillary and macular area VD significantly decreased in the perimetric group. Overall, structural and functional parameters show that VF PSD was negatively correlated with VD NH and VD RPC (p = 0.007, p = 0.015); and VF MD was positively correlated with VD NH (p = 0.029), but not significantly to VD RPC (p = 0.106).OSAS is a risk factor of NTG. With aid of OCTA, whole-layer retinal capillary dropout supports that the vascular dysregulation of OSAS leads to NTG.