Surgical Outcomes of Unilateral Lateral Rectus Rectus Versus Resection Resection in Children with Convergence Insufficiency-Type Intermittent Exotropia

As we are not aware of any reports of ULR outcomes for IXT type CI, we compared ULR and RR in patients with IXT type CI. We found that the ULR was as effective as the RR procedure in the treatment of IXT type CI in terms of collapse of the ND difference and surgical success rate.

The reference value of ND differences used in classification remains somewhat controversial across studies: Burian and Spivey1.8 recommended a difference of 10-PD, which has generally been used to this day. However, Hardesty et al.2 used a 5-PD difference as a reference value, and another study used a 15-PD difference3. While Suh et al.20 used a 10-PD as a reference value in distance deviations of more than 30 PD, in deviations of less than 30 PD the value was set as one-third of the distance deviation because 10 PD would be a relatively difference significant at a small angle, and the effects of treatments on type switching might be underestimated in such cases20.21. In this study, based on the classification of Hardesty et al., the type of IC was defined as an exodeviation greater than 5 PD at near fixation than at distance, since only patients with IXT of small angles to moderate, even close binding, were included. analyze the surgical results of muscle surgery (unilateral lateral recession).

Type CI IXT is much less common than other IXT types and has been reported in only 2.8-4.2% of IXTs22.23. Many surgical methods have been used to treat IXT type CI, but surgical results are variable and generally unsatisfactory, with success rates ranging from 18 to 92%.1,6,8,9,10,11.

Under the assumption that MR has the main effect on near deflection angle and that LR plays a role mainly in distance, MR resection has been classically introduced for the treatment of CI type IXT. However, success rates of unilateral or bilateral MRI resections for type IC exotropia have been reported to range from 27 to 67%, which has motivated the development of new surgeries.6,17,24,25,26. Choi and Rosenbaum6 performed unilateral or bilateral MRI resection with an adjustable suture in 21 consecutive patients with IXT type CI. The surgical success rate (10 PD esodeviation to 10 PD exodeviation) was 76.2% at the last examination. In 1995, Kraft et al.5 introduced the revised method of RR for IC type X (T) in which LR recession and MR resection were biased by distance and near deviations, respectively, and the MR was enhanced more than the LR was recessed . They reported that this surgery had a low risk of creating long-term remote postoperative esodeviations. In Wang et al.9 prospective study, surgical outcomes of revised RR were better than those of unilateral or bilateral MRI resection(s), reducing distance and near deviation. However, a high proportion of patients experienced early postoperative overcorrection.

Raab and Parks reported that correction of ND exotropia was achieved in only 28% of patients at 6 months after bilateral LR recession27. Bilateral LR recession increased to quasi-exodeviation has been described in the study by Farid and Abdelbaset17. In this study, the success rate in the ULR group was 63.3% at the last follow-up, which was higher than that obtained in previous studies of bilateral LR recession: 40% in the study by Raab and Parks27 and 50% distant and 27.2% close in the study by Farid and Abdelbaset17 after bilateral LR recession.

In our study, postoperative exodeviation and ND difference were significantly reduced in both groups; however, there was no statistically significant difference between the ULR and RR groups. The exact mechanism of the reduction in the ND difference is unclear. It appears that after a number of muscle surgeries for strabismus, the same amount of near and far exodeviation angles may not be corrected, but the larger preoperative angles (near exodeviation in cases of exotropia of CI type) can be corrected more than smaller angles (distance deviation in CI type exotropia). Therefore, a significant reduction in the mean ND difference was obtained after the ULR and RR procedures.

Moreover, the success rates were not significantly different between the two groups, and the risk of postoperative esodeviation or distant diplopia after ULR was lower than after RR. Additionally, in this study, there were no complaints for lateral gaze incomitance or diplopia from 6 months after ULR., which may be a concern when performing only recession. LR without MR resection. However, given these concerns, clinicians should perform a large amount of ULR with caution.

This study had several limitations. First, due to the design of the retrospective study, the surgical method was selected without any specific policy, although the surgeon had no preference for the ULR or RR procedure. Second, the preoperative close exodeviation angles and ND difference in the ULR group were smaller than those in the RR group; thus, a minor bias could have occurred. However, the collapse of the ND difference after ULR was obtained with results similar to those obtained after RR, and there was no statistically significant difference between the two groups. Further studies should be conducted with a prospective, randomized design with larger numbers of patients to confirm the effectiveness of ULR in patients with IXT type CI.

Despite these limitations, this study is significant in that it provides data suggesting a favorable outcome of unilateral LR recession in type CI IXT, with results comparable to those of the resect-resect procedure. In type CI IXT measuring less than 25 PD, there was no significant difference in the amount of reduction in the ND difference after surgery or the surgical success rate between ULR and RR.

In conclusion, unilateral LR recession for IXT with a CI of less than 25 PD is a useful surgical procedure as it produces similar surgical outcomes to unilateral RR.

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