The Clinical Characteristics and Surgical Treatment of Intermittent Exotropia with Lateral Incomitance

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Objective: To investigate the clinical characteristics and surgical outcomes of intermittent exotropia (IXT) with lateral incomitance (LI). Methods: This was a retrospective study. Thirty-two patients with IXT and LI were recruited from 381 patients from March 2016 to March 2017. All were evaluated for horizontal deviations in the primary position, left side and right side with the prism and alternative cover test by the same doctor. LI+ was defined as a reduction in deviation at the side gaze of ≥10△ compared to the primary position. Thirty-two patients were divided into group A (LI < 20△) and group B (LI≥20△). The deviation, IXT type, laterality and postoperative LI change were compared and analyzed between the two groups. Patients were followed up for 3 to 6 months. Two independent sample t test and Fisher accurate test were used for statistical analysis. Results: Of 381 patients, 32(8.4%) had LI before surgery. Twenty-nine patients (91%) had basic type IXT, 3(9%) had convergence insufficiency type IXT and none had pseudo- or true divergence excess. 24(75%) had unilateral LI and 8(25%) had bilateral LI. The relative values of LI, which were equal to (absolute amounts of LI / deviations at distance in the primary position)×100%, were less than 40% in 24(75%) and ≥40% in 8(25%) patients, but postoperative LI were presented in 5 patients. There were no significant differences in compositions of the IXT type, laterality, relative value of preoperative LI or postoperative LI between the two groups. The average horizontal deviations in the primary position at distance and near in group B (-55.0△ ± 7.6△, -60.0△ ± 8.9△, respectively) were greater than the deviations in group A (-38.8△ ± 12.4△, -44.8△ ± 12.6△, respectively) (t=-3.49, -3.16, P < 0.05). However, there was no difference in the relative value of LI between the two groups (29.7% ± 10.4%, 35.0% ± 7.6%, respectively. After surgeries, the horizontal deviation in the primary position ranged +2△ to -8△ in all patients. Conclusions: The basic type and unilateral LI are common in IXT with LI. The absolute amount of LI maybe higher in IXT with a greater deviation. We consider LI defined by the absolute amounts may be more reliable. Consideration of the side effects of LI on surgery, an optimal surgical plan could make LI negative and avoid overcorrection in the primary position. Key words: Key words: intermittent exotropia; lateral incomitance; deviation; surgery