ObjectiveTo observe the morphological characteristics of internal carotid artery (ICA) siphon and ophthalmic artery (OA) in patients with non-arteritic anterior ischemic optic neuropathy (NAION) based on CT angiography (CTA) three-dimensional reconstruction of ICA siphon and OA models. MethodsA retrospective cohort study. From January 2017 to January 2019, 26 patients with 31 eyes (NAION group) who were diagnosed with NAION by ophthalmic examination at Beijing Friendship Hospital, Capital Medical Universitywere included in the study. Among them, there were 11 males with 13 eyes, and 15 females with 18 eyes; the age was 67.52±6.30 years old. Nineteen eyes of 19 non-affected contralateral eyes were selected as the contralateral eye group. Among them, there were 9 males with 9 eyes and 10 females with 10 eyes; the age was 65.95±5.66 years old. Twenty-six eyes of 26 age- and sex-matched subjects with normal fundus examination during the same period were selected as the normal control group. All subjects underwent best corrected visual acuity (BCVA), intraocular pressure, fundus photography and CTA examination. The data obtained from CT scans were reconstructed by 3D model, and the anatomical morphology of ICA siphon was divided into U-shape, V-shape, C-shape and S-shape; the diameter of ICA siphon portion and the diameter at the beginning of OA were measured. One-way analysis of variance was used to compare the diameter of the OA at the beginning of the OA and the diameter of the ICA siphon between the three groups of eyes. ResultsThe diameters at the beginning of OA in the NAION group, the contralateral eye group, and the normal control group were 1.17±0.20, 1.34±0.17, and 1.39±0.15 mm, respectively, and the differences among the three groups were statistically significant (F=12.325, P<0.05); there was no significant difference between the contralateral eye group and the normal control group (P=0.310). In the NAION group, the anatomical morphology of the ICA siphon was U-shaped and V-shaped in 20 (64.52%) and 8 (25.81%) eyes respectively, and S and C-shaped in 3 eyes (9.67%); in the contralateral eye group, in the control group, the ICA siphon shape of the eyes examined was U-shaped and V-shaped, and S-shaped and C-shaped were rare. The diameters of the ICA siphons in the NAION group, the contralateral eye group, and the normal control group were 3.50±0.69, 3.22±0.59, and 3.55±0.54 mm, respectively. There was no significant difference between the three groups (F=1.860, P=0.163). ConclusionU-shaped and V-shaped ICA siphons are more common in NAION-affected eyes; the diameter of the starting point of OA is significantly reduced.