Objective: To evaluate optical quality and correlation factors in thyroid-associated ophthalmopathy (TAO) patients using a double-pass system. Methods: In this case control study, 31 TAO patients (62 eyes), including 28 eyes in an active stage and 34 eyes in an inactive stage, and 31 normal controls (62 eyes) were recruited from Sichuan Provincial People's Hospital from October 2016 to June 2017. Three Optical Quality Analysis System (OQAS) values at 100%, 20%, 9% contrast (OVl00%, OV20%, and OV9%), objective scatter index (OSI), modulation transfer function cutoff (MTFcutoff), Strehl ratio (SR), and mean OSI reflecting the change of tear film were measured with an OQAS visual quality analyzing system. Clinical activity score (CAS) and NO SPECS grading were performed for TAO patients. Visual acuity, intraocular pressure (IOP), height of the palpebral fissure, eyelid lag, proptosis, lagophthalmos, Schirmer Ⅰand tear film break-up time (BUT) were evaluated. An independent samples t test or Mann-Whitney U test were used to compare the quantitative data between the two groups. A Chi-square test was used to compare the qualitative data between the two groups. The Spearman correlation test was performed for data analysis. Results: Optical quality parameters including OVl00%, OV20%, OV9%, MTFcutoff, and SR had significantly decreased, and OSI and mean OSI had significantly improved in TAO patients compared with that of normal controls (all P<0.05). No statistically significant differences were found in any optical quality parameters or the Schirmer Ⅰ test in TAO patients between the active stage group and inactive stage group. However, the differences in the height of the palpebral fissure, eyelid lag, proptosis, lagophthalmos,IOP and BUT were statistically significantly between the two groups (all P<0.05). The OSI in patients with TAO was negatively correlated with the height of the palpebral fissure (r=-0.296, P=0.020), and positively correlated with NO SPECS, age and mean OSI (r=0.469, P<0.001; r=0.429, P=0.001; r=0.836, P<0.001). The mean OSI in patients with TAO was negatively correlated with the height of the palpebral fissure(r=-0.252, P=0.048), and positively correlated with NO SPECS, age and IOP (r=0.404, P=0.001; r=0.347,
P=0.006; r=0.311, P=0.014). Both OSI and mean OSI were not significantly correlated with eyelid lag, proptosis, lagophthalmos, CAS, BUT, or SchirmerⅠ. Conclusions: TAO patients have a lower optical quality and more serious dry eye compared with that of normal people. Age, height of palpebral fissure, NO SPECS and mean OSI are related to optical quality in TAO patients.