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Abstract
Aims To compare prospectively the surgical outcomes of different surgery procedures for convergence insufficiency (CI)-type intermittent exotropia (IXT) in children.
Methods Forty-five children with CI-type IXT were included in this prospective surgical study with 6 months follow-up. According to the different surgical procedures, all children were randomly divided into three groups: the unilateral medial rectus resection (UMR) group (15 cases), the bilateral medial rectus resections (BMR) group (14 cases) and the improved unilateral recession-resection (R&R) group (16 cases). In the UMR and BMR groups, the medial rectus resection(s) were based on the distance exodeviation. In the R&R group, UMR was based on the near exodeviation while lateral rectus recession was based on the distance exodeviation. A successful surgical alignment was defined as the distant deviation in the primary gaze to be between ≤10 prism dioptres (PD) of exophoria/tropia and ≤5 PD of esophoria/tropia. The success rate, the preoperative and postoperative deviations at distance and near and near-distance differences among groups were compared.
Results At the last follow-up of 6 months, the success rate in the R&R (87.5%) group was significantly higher than those in the UMR (13.3%) and BMR (42.9%) groups (p=0.000 and 0.008); the mean exodeviations at distance and near in the R&R group were significantly different from those in the UMR and BMR groups (p=0.000 and 0.001); there were no significant differences in the mean near-distance differences between the R&R group and the other two groups (p>0.05).
Conclusions The improved R&R procedure in which medial rectus resection based on the near deviation with lateral rectus recession based on the distant deviation has a better alignment than the UMR and BMR surgeries for the treatment of children with CI-type IXT. All the UMR, BMR and improved R&R surgery can reduce near-distance differences in children with CI-type IXT.
- Child health (paediatrics)
- Muscles
- Treatment Surgery
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Introduction
Convergence insufficiency (CI)-type intermittent exotropia (IXT) is characterised by a greater exodeviation at near fixation than at distance by 10 prism dioptres (PD) or more. The operation styles have been optimised to date due to the unsatisfactory outcomes of existing operation modalities for patients with CI-type IXT. The various surgical treatments for CI-type IXT include bilateral lateral rectus recession (BLR)/bilateral medial rectus resection (BMR) with or without a slanting procedure,1–9 unilateral medial rectus resection (UMR) with or without a slanting procedure,10 ,11 conventional unilateral lateral rectus recession with medial rectus resection (R&R)12 or medial rectus resection(s) with an adjustable suture.13 The surgical success rates range from 18 to 92% in these reports. Kraft et al14 first suggested a new unilateral recession-resection surgery biased to medial rectus strengthening more than lateral rectus weakening for treatment of exotropia with convergence weakness, that is, UMR based on the near deviation with lateral rectus recession based on the distant deviation. The approach can successfully collapse the near-distance differences while satisfactorily aligning both distance and near fixation. Choi et al15 successfully applied this procedure in 14 children with CI-type IXT and reduced both distance and near deviations and collapsed near-distance differences. Yang and Jeong-Min16 retrospectively observed CI-type IXT children and found that the cumulative probabilities of success at 2 years after the improved R&R surgery were 100% in the true-CI (near-distance differences ≥10 PD before and after occlusion) and masked-CI (near-distance differences <10 PD before occlusion and ≥10 PD after occlusion) type IXT groups. However, there is still dearth of a prospective and comparative study between the improved R&R surgery and other procedures. Further studies are still necessary to confirm the effectiveness of the improved R&R surgery in cases of CI-type IXT. In this paper, we prospectively compared the surgical outcomes of the improved R&R surgery, UMR and conventional BMR for treatment of children with CI-type IXT with a follow-up period of 6 months.
Methods
In this prospective study, we treated 45 consecutive children with CI-type IXT between March 2009 and September 2012. Informed written consent for the surgical procedures was obtained from parents or guardians of the children before surgery according to a protocol approved by the Medical Ethics Committee of Provincial Hospital affiliated to Shandong University for the protection of human subjects (Declaration of Helsinki). Inclusion criteria were as follows: the patients with CI-type IXT (greater at near than at distance by 10 PD or more after 60 min monocular patching, which was confirmed at repeated examinations at intervals of at least 2 weeks); age from 3 to 15 years at the time of surgery; best-corrected visual acuity in the worse eye 20/40 or better and exodeviation at distance between 15 and 25 PD by the prism and alternate cover test (PACT) with appropriate optical correction. Patients with histories of strabismus surgery, amblyopia, anisometropia greater than 2.50 D, hyperopia or myopia greater than 5.00 D spherical equivalent in either eye, coexisting vertical deviation greater than 5 PD, paralytic or restrictive strabismus, A or V pattern, oblique muscle overaction, ocular disease other than strabismus, congenital anomalies or neurological disorders were excluded from the study.
Eye examinations
Each patient underwent detailed enquiry with regard to the disease history. Near stereoacuity was assessed with Randot stereotest in current refractive correction first, then ophthalmologic and orthoptic examinations were carried out including best-corrected visual acuity, cycloplegic refraction, motility evaluation, anterior segment assessment and fundus examination. PACT was used to measure the preoperative and postoperative deviation at both distance (6 m) and near (33 cm) with fixation on accommodative targets. PACT was performed again after 1 h monocular occlusion of the non-dominant eye preoperatively in all patients. According to the difference of deviations between distance and near after monocular occlusion, IXT was classified based on the Burian's classification system.17 ,18 Only the CI-type IXT was included in this study.
Surgical dose and postoperative management
According to the different surgical procedures, all patients were randomly divided into three groups: UMR group, BMR group and improved R&R group. Based on binocular fixation preference testing, the non-dominated eye or the more often exotropic eye of patients in the UMR and R&R groups was selected for surgery. The magnitude of deviation for which to perform surgery was the largest preoperative deviation measured after 1 h monocular occlusion at distance or near fixation by PACT. In the UMR and BMR groups, the medial rectus resection(s) were based on the distance exodeviation according to our previous clinical experience. Resection of unilateral medial rectus muscle, with a surgical dosage calculated by doubling the angle of strabismus, was the surgical target for patients in the UMR group. In the R&R group, UMR was based on the near exodeviation while lateral rectus recession was based on the distance exodeviation. The surgical dosages for UMR and lateral rectus recession in the R&R group also were calculated by doubling the angle of strabismus. For example, for a patient with a distance exodeviation of 15 PD and a near exodeviation of 30 PD, the surgical dosage of unilateral lateral rectus recession was 4 mm and that of UMR 5.5 mm. Surgical dosage in this study is given in table 1.19
Surgical dosage in this study
All patients received general anaesthesia. All surgeries were performed by one of the authors (LW) together with a resident assistant using conjunctival cul-de-sac incision. For lateral rectus recession, it was measured from the back of the insertion of the muscle after muscle disinsertion and the muscle was sutured directly to the globe. For medial rectus resection, the measurement of surgical dose was made from the insertion of the muscle prior to muscle disinsertion.
The follow-up intervals after operation were determined according to the postoperative status of each patient, but examinations were usually scheduled at postoperative 1 day, 6 weeks, 3 months and 6 months. Randot stereotest and PACT at both distance and near were tested at each postoperative examination. Full-time patching for one eye was performed in patients with diplopia associated with the initial postoperative overcorrection. Hypermetropia of the overcorrected patients would be fully corrected if a consecutive esotropia persists for more than 2 weeks. If a constant esotropia of at least 6 PD at distance and near persisted for 4 weeks, base-out press-on Fresnel prism was prescribed to allow constant fusion until the esotropia was resolved. Reoperation for consecutive esotropia was performed if constant esotropia ≥10 PD persisted for more than 6 months postoperatively.
A successful surgical alignment was defined as the distant deviation in the primary gaze to be between ≤10 PD of exophoria/tropia and ≤5 PD of esophoria/tropia. Undercorrection was defined as an alignment of >10 PD of exotropia, and overcorrection was defined as >5 PD of esotropia.16 Normal stereopsis was defined as near stereoacuity within age-referenced normal thresholds published by Birch et al.20 All analyses were performed with statistical software (StatLab, SPSS for Windows V.17.0). Univariate analysis of variance was used to compare preoperative numerical data among three groups. Repeated measures analysis of variance was used to compare the preoperative and postoperative deviations at distance and near, near-distance differences among groups. A χ2 test was applied to compare the success rates among groups. A p value of <0.05 was considered statistically significant.
Results
A total of 45 patients were included, with 15 patients in the UMR group, 14 patients in the BMR group and 16 patients in the R&R group. Preoperative characteristics of patients in the three groups are shown in table 2.
Preoperative characteristics of patients with convergence insufficiency-type IXT
Surgical success
Table 3 shows the surgical outcomes of patients in the three groups. At the last follow-up of 6 months, the success rate in the R&R group was significantly higher than those in the UMR and BMR groups (p=0.000 and 0.008). However, there was no significant difference in the success rates between the UMR and BMR groups (p=0.071). In the R&R group, there were 12 of 13 children with the initial postoperative overcorrection that resolved in 4 weeks postoperatively by full-time patching for one eye, and there was only one child who used base-out press-on Fresnel prism to maintain binocular fusion. In the BMR group, there were 5 of 14 children with the initial postoperative overcorrection that all resolved in 4 weeks postoperatively by the patching therapy.
Surgical outcomes of patients with convergence insufficiency-type IXT at 6 months follow-up
Angle of deviation
The mean distance deviations preoperatively and at the postoperative follow-up points are shown in figure 1 and table 4. At postoperative day 1, overcorrection was more prominent in the R&R group than in the UMR (p=0.000) and BMR groups (p=0.001). Then, exotropic drift of ocular alignment was observed during the postoperative 6-month period in all the three groups. However, the greatest amounts of exotropic drift at distance occurred during the postoperative 6-week period in the R&R group. At the last follow-up of 6 months, the mean distance exodeviations in the three groups were significantly reduced in comparison with those before surgery (UMR group, p=0.004; BMR group, p=0.003 and R&R group, p=0.000). At the last follow-up, the mean exodeviation at distance in the R&R group was significantly different from those in the UMR and BMR groups (p=0.000 and 0.001); however, there was no significant difference in the mean exodeviations at distance between the UMR and BMR groups (p=0.080).
Preoperative and postoperative angles of deviation (mean±SD)
The mean distance deviations preoperatively and at the postoperative follow-up points in the unilateral medial rectus resection, bilateral medial rectus resection and unilateral lateral rectus recession and medial rectus resection groups.
The mean near deviations preoperatively and at the postoperative follow-up points are shown in figure 2 and table 4. The near deviation at postoperative day 1 and the exotropic drift of ocular alignment at near was similar to those at distance in the three groups. At the last follow-up of 6 months, the mean near exodeviations in the three groups were significantly reduced in comparison with those before surgery (p=0.000 in the three groups). At the last follow-up, the mean near exodeviation in the R&R group was significantly different from those in the UMR and BMR groups (p=0.000 and 0.001); however, there was no significant difference in the mean near exodeviations between the UMR group and BMR groups (p=0.989).
The mean near deviations preoperatively and at the postoperative follow-up points in the unilateral medial rectus resection, bilateral medial rectus resection and unilateral lateral rectus recession and medial rectus resection groups.
The mean near-distance differences were significantly reduced at postoperative 6 months in the three groups (figure 3 and table 4) in comparison with those before surgery. They were reduced from 11.3±2.1 PD to 1.5±7.6 PD (range −16 to 14 PD; p=0.000) in the UMR group, 12.3±2.5 PD to 5.0±5.2 PD (range −2 to 14 PD; p=0.000) in the BMR group and 12.1±3.6 PD to 1.9±2.7 PD (range −4 to 6 PD P=0.000) in the R&R group. At the last follow-up, the mean near-distance difference in the UMR group was significantly different from that in the BMR group (p=0.036); however, there were no significant differences in the mean near-distance differences between the R&R group and the other two groups (p> 0.05).
The mean near-distance differences preoperatively and at the postoperative follow-up points in the unilateral medial rectus resection, bilateral medial rectus resection and unilateral lateral rectus recession and medial rectus resection groups.
Near stereopsis
At postoperative 6 months, the normal near stereoacuity occurred in 76.9% (10/13), 90.9% (10/11) and 85.7% (12/14) of children who could understand Randot stereotest in the UMR, BMR and R&R groups, respectively. There were no significant differences in the rates of normal near stereopsis among the three groups after surgery (p=0.632).
Lateral incomitance and complications
In this series, no patient had a 10 PD or more lateral incomitance in side gaze at final follow-up examination. A conjunctival cyst occurred in one patient followed by medial rectus resection and was ablated at postoperative 6 weeks.
Discussion
The purpose of surgery for CI-type IXT is to correct the near and distance exodeviations, as well as to reduce the near-distance differences. Classic teaching suggested that CI-type IXT should be treated with bilateral medial rectus resections. The success rates of the surgery ranged from 27 to 67%.1–4 Several surgery procedures with different modifications for CI-type IXT have been used in clinical practice and lead to varied clinical outcomes;2 ,4 ,5 ,7 ,10 ,11 ,13 however, none of these surgery procedures was considered as the ideal surgical method for CI-type IXT. In 1995, Kraft et al14 first described an improved R&R procedure biased to medial rectus strengthening more than lateral rectus weakening for treatment of exotropia with convergence weakness and got successful results. However, the study included only 3 children among 14 patients and 5 patients involved adjustable sutures.
Then, Choi et al15 prospectively applied this procedure for treatment of 14 children with CI-type IXT and received a success rate of 42.9% with a minimum follow-up of 1 year. The results could be better convinced if they had the control groups in their study. Afterwards, Yang and Jeong-Min16 retrospectively observed efficacy of different types of strabismus surgeries in patients with different sub-CI-type exotropia according to their response to diagnostic monocular occlusion and found that the improved R&R procedure was significantly more successful than the BLR procedure in the true-CI and masked-CI groups. They concluded that in patients with CI-type exotropia maintained after monocular occlusion, unilateral R&R surgery based on near-distance measurements was recommended.
The results of our study indicate that the improved R&R procedure was significantly better than the UMR and BMR procedures for correction of the distance and near exodeviations in patients with CI-type IXT with 6 months follow-up, although it showed a prominent overcorrection rate in the immediate postoperative period. Exotropic drift of ocular alignment was observed during the postoperative 6-month period in all the three groups, but the greatest amounts of distance and near exotropic drift in the R&R group occurred during the postoperative 6-week period. After that, the mean deviations changed a small amount, from 0.9±5.3 PD at distance and −2.0±4.8 PD at near at postoperative 6-week, to −1.1±5.6 PD at distance and −3.0±6.9 PD at near at 6 months follow-up, respectively. Seventy-one per cent of children (10/14) had immediate postoperative esodeviations at distance and/or at near in the study of Choi et al.15 But most of them (9/10) resolved during 1 month postoperatively. This is similar to our study. However, the incidence of immediate postoperative overcorrection requiring incorporated base-out prisms was 38.5% (5/13) in the true-CI group and 14.3% (1/7) in the masked-CI group after R&R surgery in the study of Yang and Jeong-Min.16
In this prospective study, the target angles for the medial rectus resection(s) in the UMR and BMR groups were based on preoperative distance but not near exodeviation for reducing a risk of postoperative distance esotropia according to our previous clinical experience. Although a higher success rate of 93.3% (14/15) in the UMR group and 64.3% (9/14) in the BMR group was achieved at postoperative day 1, the long-term success rates were lower than that in the R&R group because of exotropic drift of ocular alignment. Therefore, the target angles based on the distance exodeviation for medial rectus resection(s) in the UMR and BMR groups might be inadequate, especially for that in the UMR group.
The study of Kraft et al14 resulted in a reduction of near-distance differences from 11.9 to 1.7 PD in 14 adult patients. Choi et al15 successfully applied this improved R&R procedure in 14 children and reduced both distance and near deviation and collapsed near-distance differences from 11.3 to 4.6 PD with a low risk of long-term postoperative esotropia. In the study of Yang and Jeong-Min,16 the mean near-distance difference decreased from 11.4 to 0.8 PD, and both surgical procedures of BLRs and the improved R&R surgery were equally effective in the collapse of near-distance differences without significant esodeviation at distance. In our study, the mean near-distance differences were significantly reduced at postoperative 6 months in all the three groups in comparison with those before surgery. There were no significant differences in the mean near-distance differences between the R&R group and the other two groups at 6 months follow-up. It suggests that all the UMR, BMR and improved R&R surgeries can reduce near-distance differences in patients with CI-type IXT. However, even though the near-distance deviation differences were similar in the each group, the success rates and ocular alignment were better in the R&R group.
This study has several limitations. First, the sample size in every group is relatively small. In addition, the follow-up period of 6 months is a relatively short time because, overtime, there may be a further exotropic drift and reduction in surgical success rate. Notwithstanding its limitation, this study does suggest that the improved R&R procedure has a better alignment than the UMR and BMR surgeries for the treatment of children with CI-type IXT.
Proper management of a patient with CI-type IXT continues to be challenging for the strabismus surgeon. Future prospective and comparative studies with larger samples and longer duration of follow-up are required to confirm which type of surgery procedures is the ideal surgical method for CI-type IXT.
References
Footnotes
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Contributors LW designed this study. All authors were involved in the collection, analysis and interpretation of data, drafting and revising the manuscript and tables, including final approval.
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Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
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Competing interests None.
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Patient consent Obtained.
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Ethics approval Medical Ethics Committee of Provincial Hospital affiliated to Shandong University.
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Provenance and peer review Not commissioned; externally peer reviewed.
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