AIM: To investigate whether the subtle change of choroidal/retinal vessel densities and volumes in thyroid-associated ophthalmopathy (TAO) could be an early sign to detect dysthyroid optic neuropathy (DON). METHODS: This was a retrospective cross-sectional study, and a total of 98 eyes from 50 subjects were enrolled under certain criteria. Thirty-four eyes of normal controls and 64 eyes of TAO, including 39 eyes of DON and 25 eyes of TAO without DON, underwent optical coherence tomography angiography (OCTA) scanning. All the tested parameters of OCTA scanning including choroid radial peripapillary capillaries (RPC), retinal nerve fiber layer (RNFL), and macular ganglion cell complex (GCC) were compared among groups, and the correlation between OCTA parameters and visual function parameters was also investigated. RESULTS: Whole choroidal RPC was significantly reduced in DON (48.24%±0.4978%) compared to normal (50.33%±0.3173%) and TAO without DON (49.16%±0.5463%; P=0.0041). The reduction of whole choroidal RPC was also correlated with visual field (VF) defect in DON (r=0.5422, n=39). Although vision acuity and VF were improved in all the patients with DON after being treated with medical and surgical decompression, the reduction of RPC density were not reversed. CONCLUSION: There is a notable reduction in choroidal RPC in DON, which is correlated with VF defect. The reduction of RPC density could not be reversed immediately by medical and surgical decompression even when vision and VF were improved. These findings suggest that choroidal RPC could be a useful parameter to diagnose and monitor early stage of DON.