Torsional diplopia after orbital decompression and strabismus surgery.

PURPOSE: To investigate diplopia after orbital decompression in patients with thyroid-related orbitopathy. METHODS: We retrospectively analyzed medical records of 45 consecutive patients who had undergone orbital decompression surgery (DS) and a subgroup of 10/45 patients who underwent disinsertion of the inferior oblique (IO) muscle during DS. Diplopia was assessed before DS and 1 and 3 months after DS. Residual strabismus defects were treated surgically approximately 3 months after DS with follow-up visits 1 week, 3 months, and 6 months postoperatively. Patients with horizontal or vertical diplopia were evaluated using the alternate prism-and-cover test and torsional diplopia (TD) using a double Maddox rod test to quantitate their strabismus. RESULTS: Strabismus surgery was effective in treating the horizontal and vertical diplopia (13/40 cases with residual deviations required prism glasses), but did not resolve the TD. None of the patients with IO disinsertion during DS complained of TD before strabismus surgery. However, after strabismus surgery, TD occurred in all 10 patients with IO disinsertion vs 8/30 patients without IO disinsertion (p<0.001, Fisher exact test). Overall, TD was induced in 18/45 (40%) of the DS cohort. CONCLUSIONS: Patients with IO disinsertion during DS may be at increased risk of developing TD postoperatively. We recommend sparing or reattaching the IO muscle during DS when possible to reduce the risk of developing untreatable TD.