Adjustment of the surgical nomogram for surgery on slipped extraocular muscles.

Purpose: A slipped muscle is an underdiagnosed complication of strabismus surgery. Surgery necessitates intraoperative diagnosis, measurement, and resection of the empty sheath. We analyzed the results of empty sheath surgery for slipped medial and lateral rectus muscles in a large cohort of patients.

Methods: Eighty-five patients who underwent empty sheath surgery at a secondary referral center by a single strabismologist were included in the study. We retrospectively analyzed the preoperative and postoperative change in angle of deviation 6 weeks after surgery. All cases were reoperations in which an unexpected or unsatisfactory outcome followed primary surgery. Consecutive exotropias with slipped medial rectus muscles were noted in 68 patients. There were 17 esotropia cases with lateral rectus muscles slip, of which 2 were consecutive exotropias that became consecutive esotropias. Bilateral medial rectus muscle slips were found in 6 patients with consecutive exotropias. Adjustable suture surgery was performed in 27 patients.

Results: Resection of the empty sheath of the slipped medial or lateral rectus muscle with advancement to the original site of insertion was done in all cases; in addition, the antagonist muscle was recessed only if it was tight. The total muscle advancement was calculated in millimeters from the total amount of sheath resected, muscle advanced, and the antagonist recessed. The greater the preoperative deviation, the more surgical muscle advancement was required and the greater the change in postoperative angle of deviation. Mean change in angle of deviation was 3.13(delta) for each millimeter of muscle advancement (median = 3.00, SD = 1.72).

Conclusions: The diagnosis of slipped muscle should be confirmed during strabismus surgery. The empty sheath was measured, resected, and the muscle advanced to the original site of insertion. An approximate 3(delta) change in angle of deviation was observed for every millimeter of muscle of advancement. For very large and very small deviations, surgeons should modify this to an accustomed measurement dictated by their experience.