Vertical Deviations Improved With Release of Postoperative Inferior Oblique Muscle Inclusion

Purpose: In repeat surgery involving the horizontal extraocular muscles, it is frequently noted that the anterior fibers of the inferior oblique muscle are inadvertently caught in the lateral rectus muscle insertion. It is theorized that releasing the IO muscle inclusion (IOI) will decrease the total amount of vertical deviation associated with the horizontal misalignment in primary position. The current study shows the impact of this release on the vertical deviation. Subjects and Methods: A retrospective noncomparative analysis was used to evaluate the impact of eliminating the IOI. The subjects were 45 patients with residual horizontal strabismus found to have IOI at the time of surgery. Each patient was managed with release of the entrapped muscle along with the appropriate horizontal muscle surgery. Results: Release of the IOI muscle reduced the ipsilateral vertical deviation an average of 3.5 PD (P > 0.001) in cases of hypotropia and 5.8 PD (P > 0.001) in patients with hypertropia, with stability of alignment for a minimum of 2 years. Conclusion: Inadvertent IOI is commonly encountered in reoperative strabismus for horizontal deviations, involving partial or complete capture of the IO muscle fibers at the time of original lateral rectus muscle surgery. It is concluded that the simple release of the IO muscle fibers included in the attachment of the lateral rectus muscle will have a significant impact on reducing the vertical deviation and may avoid the need for additional vertical muscle surgery.