Inferior Oblique Muscle Recession Versus Myectomy for Inferior Oblique Overaction

To determine the effect of recession and myectomy on inferior oblique overaction (IOOA). This study was performed on 50 patients (82 eyes) scheduled for IOOA surgery who were randomly divided into two groups: recession (R) versus myectomy (M). A complete eye examination was performed before the operation. IO was cut off at its inferior temporal region when using M procedure. In the other group (R) after disinsertion, the IO muscle was sutured to 2mm lateral and 3.5 to 4mm posterior to the insertion of the inferior rectus. After at least 3 months, the same examinations were repeated. Successful surgery was defined as IOOA<+1. Twenty-five men (50%) and 25 women with the mean age of 12.3±5.9 (range 3-32) years entered the study. The surgery was performed in 18 patients unilaterally and in 32 patients bilaterally. Both myectomy and recession methods were successful in reducing IOOA (PM<0.001, PR<0.001). The amount of IOOA reduction was 2.37 in the M group and 1.92 in the R group which was not significantly different (P=0.097, using Mann-Whitney test); however, ordinal logistic regression showed a difference (P=0.016). We found primary IOOA without superior oblique underaction (SOUA) in 28 eyes in the M group and in 32 eyes in the R group. Secondary IOOA with superior oblique underaction (SOUA) was found in 14 eyes in the M and in 8 eyes in the R group, respectively. In patients with more initial IOOA, the outcomes of both methods were better compared to patients with less initial overaction. There was no statistically significant difference in postoperative function of IO between these two methods of surgery (P=0.051). Both methods resulted in equal improvements in SOUA and V-pattern. Complications included new hypertropia (2%), new DVD (dissociated vertical deviation) (8%) and asymmetry (2%). Both recession and myectomy have significant weakening effect on IOOA. Myectomy results in more normal function of IOOA but IOUA is also higher with this method. Both methods are more effective if the initial overaction is higher.