Asymmetrical bilateral paresis of the superior oblique muscle

Abstract

Background: To review the preoperative signs of bilateral superior oblique paresis and to analyze their presence.

Methods: The proposed preoperative signs of bilateral superior oblique (SO) muscle paresis were separated into "certain signs" and "suspicious signs." The signs were analyzed for accuracy using case examples and statistics.

Results: A strong preoperative sign of bilateral SO muscle paresis was reversal of the hypertropia in the ipsilateral (and/or ipsi-supralateral) position and/or in the contralateral head tilt position. In such cases, the addition of a light contralateral weakening procedure to the operation aimed at the elimination of the hypertropia caused by the more affected SO muscle prevented development of the clinical picture of a contralateral SO muscle paresis. A suggestive preoperative sign of bilateral SO muscle weakness was marked reduction of the hypertropia in the ipsilateral (and ipsi-supralateral) position, as well as in the contralateral head tilt position. In these cases, a contralateral inferior oblique muscle weakening was deferred until after motility could be reassessed postoperatively. An additional sign of possible bilateral SO muscle weakness was the presence of a large V pattern.

Conclusions: When planning surgery for apparent unilateral SO muscle paresis, the surgeon should be aware of the often subtle preoperative signs of bilateral SO muscle paresis. Early diagnosis allows the surgeon to avoid the reversal of the clinical picture or to advise the patient of the possibility of a bilateral problem.