Torsional incomitance after asymmetrically adjusted Harada-Ito procedures for the simultaneous correction of vertical and torsional deviations in bilateral trochlear nerve palsy

Background: Adjustable bilateral Harada-Ito procedures have been described, sometimes with asymmetric adjustment used to correct vertical misalignment when coexisting with torsional strabismus. We investigated the causes of significant postoperative torsional incomitance noted in some patients undergoing these procedures. Methods: The medical records of patients who underwent bilateral Harada-Ito procedures for bilateral trochlear nerve palsy between 1980 and 2018 were reviewed retrospectively. Cases with simultaneous operation on any other oblique or vertical rectus muscle were excluded. Surgical results, especially using Lancaster red-green (Lan R-G) plots, were correlated with the procedures performed. Results: A total of 17 patients were included. At their last follow-up visit (mean, 12 months after surgery), 9 were diplopia free. Of the 8 with continuing diplopia, 2 had undercorrection and 1 had Brown syndrome. In 5 patients with continuing diplopia, there was relative intorsion of the eye movement paths in upgaze and relative extorsion of these paths in downgaze, a type of torsional incomitance. Asymmetric adjustment with tightening of one superior oblique tendon, and often loosening of the contralateral superior oblique tendon, had been performed in those 5 cases. Only 1 of the successful cases had the same type of asymmetric adjustment. There was a positive association between the severity of the preoperative Lan R-G pattern and postoperative diplopia. Conclusions: Asymmetric adjustment of bilateral Harada-Ito procedures when attempting to correct the coexisting vertical misalignment can cause significant torsional incomitance with incomplete correction of extorsion in downgaze and intorsion in upgaze. This pattern may result in postoperative diplopia that is surgically challenging to correct.[Formula