MASKED BILATERAL SUPERIOR OBLIQUE MUSCLE PARESIS - A SIMPLE OVERCORRECTION PHENOMENON

Objective: This study aimed to determine a mechanism by which the mask ed bilateral superior oblique muscle paresis phenomenon may be explain ed. Design: A retrospective study of the authors' patients with the pr eoperative diagnosis of a unilateral superior oblique muscle paresis w as performed. Patients in whom an apparent contralateral superior obli que muscle paresis developed after surgery (masked bilateral superior oblique muscle paresis) were compared with those patients in whom this condition did not develop. Participants: One hundred eight patients p articipated. Results: Of the 108 patients studied, 30 (27.7%) patients had signs of an apparent superior oblique muscle paresis develop in t he contralateral eye after surgery. In comparing those patients in who m an apparent contralateral superior oblique muscle paresis did develo p after surgery with those patients in whom this finding did not devel op, no significant differences were found in the age at surgery; etiol ogy (traumatic vs, nontraumatic); average hyperdeviations in primary g aze, ipsilateral and contralateral gazes, and ipsilateral and contrala teral head tilts; average V pattern; inferior and superior oblique mus cle function; extorsion on double Maddox rod testing; and objective fu ndus extorsion.Conclusion: Analysis of the authors' data showed that a surgical overcorrection of a unilateral superior oblique muscle pares is can masquerade as an apparent contralateral superior oblique muscle paresis, This is caused by a persistence of the head tilt and side ga ze misalignment pattern from the original superior oblique muscle pare sis.