Clinical characteristics of thyroid eye disease with restrictive strabismus

Purpose Restrictive strabismus is a major cause of diplopia and impaired quality of life in thyroid eye disease (TED), but its clinical and imaging characteristics remain incompletely understood. This study investigated the clinical and magnetic resonance imaging (MRI) characteristics of TED patients with restrictive strabismus at initial presentation. Methods Among 5,234 TED patients treated between 2009 and 2024, 339 patients (6.5%) with clinically confirmed restrictive strabismus and supportive MRI findings were retrospectively included. Restrictive strabismus was confirmed primarily by positive forced duction testing with limitation of ocular rotations. Clinical characteristics, thyroid function, Clinical Activity Score (CAS), NOSPECS classification, strabismus type, and orbital MRI findings were analyzed. Contrast-enhanced orbital MRI, including T1-weighted and fat-suppressed T2-weighted sequences, was used to evaluate extraocular muscle enlargement, inflammation, and edema. Results Patients with active extraocular muscles had higher CAS scores than those with stable muscles ( P < 0.01). Monocular-onset patients showed higher CAS and NOSPECS scores (both P < 0.01). Hyperthyroid patients had higher NOSPECS scores than euthyroid patients ( P < 0.01). Longer disease duration before presentation was associated with smaller muscle area, less inflammation, and reduced edema, whereas higher CAS scores correlated with larger muscle area and more severe edema. Conclusions TED patients with restrictive strabismus were predominantly male and commonly showed binocular involvement and hyperthyroidism. Inferior rectus involvement was the most common imaging finding, especially in vertical strabismus. Orbital MRI may help evaluate extraocular muscle activity and guide strabismus surgery timing.