Inferior oblique syndrome : an under-recognised complication of strabismus surgery

Purpose To show the predictive factors that would indicate the possibility of inferior oblique inclusion when considering surgery on a previously operated lateral rectus muscle. We also aim to highlight the importance of freeing any inferior oblique attachment to the lateral rectus muscle during either a resection or a recession procedure. Methods A retrospective review was undertaken of 39 patients who had previously had horizontal muscle surgery. Pre- and post-operative ocular position and rotations were compared. Using the hypothesis that a vertical element to the strabismus or a deficiency of vertical ocular rotation may result from inclusion of inferior oblique fibres during lateral rectus surgery, we compared the groups using the Fisher Exact two-tailed test. Results Eight of the 39 patients were identified as having inferior oblique inclusion. Six were found to have a vertical deviation in the primary position and 6 a deficiency of vertical rotation. Conclusion A vertical deviation or a deficiency of vertical rotation are significant predictors of inferior oblique inclusion into the lateral rectus insertion. Re-operation to free the inferior oblique fibres often fails to reduce the vertical deviation, and hence there is a need for careful dissection of the inferior oblique during the primary surgery.