Superior oblique muscle involvement in thyroid ophthalmopathy.

Background: Rectus muscle involvement in thyroid ophthalmopathy is well documented. The inferior rectus is the most frequently involved, followed by the medial, superior, and infrequently the lateral rectus. This study reports involvement of the superior oblique muscle as a contributory cause of restrictive strabismus in patients with thyroid ophthalmopathy.

Methods: This is a retrospective review of four patients with known thyroid ophthalmopathy who presented with incomitant vertical strabismus, A-pattern, overdepression in adduction, underelevation in adduction, and incyclotorsion. All patients underwent preoperative orbital imaging. Two of the four patients had previous orbital decompressions. All patients underwent surgery on the SO muscle.

Results: Preoperative scans showed enlargement of one or both SO muscles in all patients and intraoperative forced duction testing revealed restriction to elevation in adduction in all cases. Preoperative A-pattern ranged from to 6 to 22 prism diopters. All subjects had preoperative incyclotorsion, ranging from 2 and 14 degrees. Improvement of the versions, hypertropia, and cyclotorsion followed surgical weakening procedures on the SO muscle.

Conclusion: Thyroid ophthalmopathy may involve the SO muscle. Clinical manifestations include preoperative A-pattern strabismus, incyclotorsion, and restrictive limitation to elevation in adduction. Orbital imaging documents SO muscle enlargement. Awareness of SO involvement in thyroid ophthalmopathy assists the surgeon to develop a more precise surgical strategy to correct the hypotropia.