The purpose of this paper is to investigate how much correction is obtained per millimeter of medial rectus (MR) resection for recurrent exotropia after bilateral lateral rectus (BLR) recession, and to determine the difference in the effects between unilateral and bilateral resection, and the influence of previous lateral rectus (LR) recession on the effects of MR resection. A total of 59 patients who had undergone MR resection after BLR recession were included in this study. The unilateral group consisted of 38 patients and bilateral group, 21 patients. Thirty patients in the unilateral group were divided into two groups: patients who had undergone previous LR recession of 7 mm or greater (21 patients) and less than 7 mm (9 patients). Main outcome measures were average deviation corrected per millimeter of MR resection at 1 month postoperative. The average effect of MR resection was 4.2 prism diopters (PD, 2.0 to 6.7 PD)/mm. The average effect in the unilateral group was 4.2 PD/mm and 4.1 PD/mm in the bilateral group. There was no significant difference between groups (P = 0.60). The average effect in the recession 7 mm or greater group was 4.0 PD/mm, and the average effect in the recession less than 7 mm group was 4.2 PD/mm (P = 0.698). The effect of MR resection per millimeter was variable. The laterality and previous amount of LR recession did not influence the effect of MR resection. These variable outcomes dictate that caution be exercised when MR resection is performed for recurrent exotropia.
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