PurposeTo investigate the changes in the choroidal structure in patients with inactive Graves Ophthalmopathy (GO). DesignA prospective, masked, observational cross-sectional study. MethodsChanges in choroidal vascularity index (CVI) were studied in the patients with inactive GO using binarization on enhanced depth imaging optical coherence tomography (EDI-OCT) images. Choroidal area, subfoveal choroidal thickness (SFCT), stromal area, luminal area, CVI and retinal nerve fiber layer (RNFL) thickness was used to compare the eyes of sixty-four age-, gender-matched healthy subjects. All measurements were done separately both subfoveal (1500 µm) and total choroidal area (7500 µm). The relation between CVI or SFCT and age, gender, duration of disease, the severity of disease, TRAb (thyrotropin receptor autoantibody), smoking status, and exophthalmometer readings were evaluated. ResultsThere were 56 patients (30 female, 26 male; mean age: 39.5 ± 11.4 years) in the GO group and 64 patients (34 female, 30 male; mean age: 42.2 ± 5.6 years) in the healthy subject group. There was no statistically significant difference between subjects with GO and healthy controls regarding age (p = 0.24) and gender distribution (p = 0.55). Patients with GO had significantly higher intraocular pressure (p = 0.001) and exophthalmometer readings (p = 0.0001) than the healthy controls. The SFCT, CVI1500 and the stromal area1500 was significantly different between the groups (p = 0.009, p = 0.009, p = 0.011, respectively). Multivariate analysis showed that age (-0.871, p = 0.02) was highly correlated with the decreased SFCT, and duration of disease (0.524, p = 0.001) was significantly positively correlated with SFCT. Luminal area1500 (-0.416, p = 0.0001)and stromal area1500 (-0.657, p = 0.0001) were significantly negatively correlated with CVI1500 in the patients with GO. ConclusionAlthough higher CVI1500 was observed in GO patients than in healthy controls, the degree of increase was not the same in the CVI7500. Age and duration of disease significantly affect the SFCT, and luminal area1500 and stromal area1500 significantly affect the CVI1500.