Postoperative drift and doseresponse of strabismus surgery in thyroid eye disease: predicting desired outcomes with intraoperative adjustable sutures

Objective: To report outcomes of strabismus surgery in thyroid eye disease using intraoperative bow-knot adjustable sutures under topical anaesthesia and calculate prediction models for surgical correction and postoperative drift depending on surgical dose-response. Methods: We retrospectively reviewed patients operated on from 2016 to 2021. A satisfactory outcome was defined as no diplopia with maintenance of vertical (<5 PD) and horizontal (<10 PD) stable alignment at primary gaze. Subjective diplopia corrected with prisms within successful motor alignment was defined as a fair result. Otherwise, the result was considered to be poor. Results: A total of 73 patients were included (60 females, 82%). Mean preoperative horizontal and vertical deviations were 26.9 PD (19.1 SD), and 11.8 PD (7.6 SD), respectively. Mean horizontal drift was -3.2 PD (5.2 SD), whereas mean vertical drift was -3.4 PD (3.3 SD). A linear regression established a dose-response of 2.37 PD/mm for each medial rectus recession (p < 0.0001; r(2) = 0.777) and 3.75 PD/mm for unilateral inferior rectus recession (p < 0.0001; r(2) = 0.922). Final success rate was satisfactory in 62 patients (85%), fair in 7 patients (10%), and poor in 4 patients (5%). Conclusions: Muscle recession with intraoperative adjustable sutures is effective for the treatment of thyroid eye disease strabismus. Predictable dose-responses could be achieved with a drift toward overcorrection. Undercorrection proportional to the planned surgical dose should be the immediate postoperative target of choice. Other variables such as orbital decompression and concurrent vertical and horizontal surgery do not correlate with dose-response and postoperative drift. However, further studies are necessary to validate our findings.