Strabismus Surgery in Thyroid-Associated Ophthalmopathy; Surgical Outcomes and Surgical Dose Responses

Purpose: To investigate the success rate and surgical dose responses in strabismus surgery of thyroid-associated ophthalmopathy (TAO). Methods: Thirty-three patients (26 men) were included in this study and underwent strabismus surgery. The mean follow-up time was 11.3 ± 6.5 months. Success was defined as the proportion of patients with a horizontal deviation of less than 10 PD, vertical deviation of less than 4 PD, and no subjective diplopia in primary and downgaze. Results: After the final follow-up visit, strabismus surgery was successful in 87.8% of patients. Pre-operative factors (age, gender, smoking, corticosteroid usage, radioactive iodine, orbital decompression, optic neuropathy, baseline deviations, extorsion, type of strabismus, TAO duration) were not statistically correlated with success. Dose responses were calculated to be 3.44 ± 0.66 PD/mm of medial rectus recession and 4.83 ± 1.48 PD/mm for vertical rectus recession. Patients with deviation ≥25 PD had significantly larger surgical dose response compared to the group with deviation<25 PD (p value = .003 for horizontal and p-value <0.05 for vertical deviations). In eyes with predominant hypotropia, we found 1.64 ± 1.37 PD decrease in esotropia for each millimeter recession of inferior rectus muscle. Conclusions: Surgical dose responses in large deviations were significantly higher than the moderate angle of deviation. The reported mean for vertical dose responses may vary in different patients based on the laterality and involvement of superior rectus muscles. The recession of inferior rectus muscle may correct mild-to-moderate esotropia without the need for horizontal muscle surgery.