Purpose To assess with Bézier curves the outcomes of Müllerotomy with anterior graded Müller muscle disinsertion for the treatment of Graves upper eyelid retraction (UER). Methods Eighty-six eyelids of 52 inactive GO patients operated from November 2018 to June 2021 were included in this study. All measurements were performed on Bézier curves adjusted to the upper lid contour with a previously validated algorithm. Lid contour was classified regarding grade of superposition (GS) as excellent (GS > 90%), good (GS 85–90%) or poor (< 85%). Surgical success was defined as complete or partial if postoperative grade of asymmetry was < 10% with an excellent or good lid contour, respectively. Results The mean age was 51 ± 10.4 years with a range from 31 to 78 years and a mean follow-up of 14.4 ± 7.4 months. There was a significant improvement of median GS ( p  < 0.0001) from preoperative (74.3%; 10.7 IQR) to postoperative values (91.7%; 6.3 IQR). A normalization of postoperative contour peak (− 0.69; 1.27 SD) and MPLD90 (4.2 mm; 0.8 SD) was noticed ( p  < 0.0001). Postoperative lid contour was excellent in 62 (72%), good in 16 (19%) and poor in 8 eyelids (9%). Surgical success was achieved in 42 patients (81%), from which 34 (81%) were complete. Reintervention was required in 14 eyelids (16%). Conclusions Measuring surgical outcomes with Bézier curves allows an automated, complete and objective assessment, giving more consistency to our data compared to previous reports. Müllerotomy with graded Müller muscle disinsertion is a safe and effective procedure for Graves UER, offering predictable results.