Response of coexisting underacting superior oblique and overacting inferior oblique muscles to inferior oblique weakening.

One hundred twenty-six eyes with inferior oblique overaction and coexisting superior oblique underaction were retrospectively studied pre- and postoperatively. The data show that weakening the inferior oblique corrected the underaction of the superior oblique, and that overcorrection of the underacting superior oblique was unusual. Eyes were selected for study if superior oblique underaction coexisted with inferior oblique overaction preoperatively. The operation chosen for the inferior oblique in every case was determined by the quantity of inferior oblique overaction and whether prior surgery on the inferior oblique had been performed. A denervation and extirpation was the final inferior oblique weakening procedure in all except three of these eyes. Congenital or acquired superior oblique palsy cases were not included in this study. To eliminate eyes with superior oblique palsy, we excluded any patient with a history of serious head trauma; a vertical deviation in the primary position greater than 5 prism diopters except if caused by dissociated vertical deviation; the complaint of torsional diplopia controlled by an anomalous head posture; or a positive Bielschowsky head tilt test. The mean preoperative superior oblique action was -2.4 on a scale of 0 to 4, and this corrected to a mean postoperative action of -0.2, (P less than .001). This was accompanied by a change in the mean inferior oblique action of +3.8 to -0.2, (P less than .001). These same results were found regardless of the preoperative action of either the inferior or superior oblique. With regard to the postoperative superior oblique action, 22 cases were undercorrected, 2 were overcorrected, and 102 were normal.