Purpose
To conduct a comparison of the long-term surgical outcomes of bilateral lateral rectus recession (BLR) vs unilateral lateral rectus recession–medial rectus resection (RR) in treatment of intermittent exotropia.
Design
Nonrandomized, retrospective case series.
Methods
Consecutive patients who underwent BLR or RR for treatment of intermittent exotropia between 2002 and 2006 and had ≥2 years’ follow-up were recruited. Surgical outcomes were grouped according to postoperative angle of deviation as overcorrection (esophoria/tropia >5 Δ), success (esophoria/tropia ≤5 Δ to exophoria/tropia ≤10 Δ), or undercorrection/recurrence (exophoria/tropia >10 Δ), and were compared between the BLR group and the RR group at postoperative 1 day, 1 month, 6 months, 1 year, and 2 years, and at the final examination.
Results
Of 128 patients, 55 underwent BLR and 73 underwent RR. The mean follow-up period was 44.2 months in the BLR group and 47.8 months in the RR group. At 1 day, 1 month, 6 months, 1 year, and 2 years after surgery, surgical outcomes in each group were not different ( P > .05) However, the final outcome at a mean of 3.8 years was significantly different between the groups, demonstrating a higher success rate in the BLR group than in the RR group (58.2% vs 27.4%, P < .01). Cumulative probability of survival from recurrence was higher in the BLR group than in the RR group ( P = .01, log-rank test). Recurrences were most common within 6 months from surgery; however, after that, recurrences occurred continuously in the RR group and rarely in the BLR group.
Conclusion
Surgical outcomes by 2 years after surgery for intermittent exotropia were not different between the BLR and RR groups. However, final outcomes were better in the BLR group than in the RR group. This may be caused by the difference of recurrence rate over time: continuous recurrence of exotropia occurred in the RR group, while recurrence was low in the BLR group after postoperative 6 months.
Intermittent exotropia is the most common divergent strabismus in childhood. Surgical correction in patients with intermittent exotropia is performed for satisfactory and stable ocular alignment and binocular function. Although surgery gives satisfactory results during the early postoperative period, quite frequently more than 1 operation is needed in order to obtain stable orthophoria. The success rate of surgery for treatment of intermittent exotropia is reported to vary from 33% to 83%, depending on the follow-up periods and the definition of recurrence of exotropia. Despite disagreement regarding the best surgical approach, the 2 most popular approaches are bilateral lateral rectus recession (BLR) and unilateral lateral rectus recession–medial rectus resection (RR).
According to findings from a number of different studies, the success rate using the BLR procedure varies from 43% to 83%, and with RR it varies from 33% to 83%. Still, there have been controversies with regard to which surgical procedure was best for treatment of intermittent exotropia. Some authors have stated that BLR provides more stable results, while others have reported a higher rate of successful outcomes with RR. Moreover, some authors have demonstrated a greater degree of subsequent exotropic shift with the RR procedure. Still, which surgical procedure produces better results over many years remains uncertain.
In this study, a retrospective review was conducted for assessment of differences in long-term surgical outcome between BLR and RR for treatment of intermittent exotropia in children, with a minimum follow-up period of 2 years.
Methods
Patients who underwent either the BLR or RR procedure for treatment of basic-type intermittent exotropia between July 1, 2002 and May 31, 2006 at Seoul National University Children’s Hospital were enrolled. Among them, consecutive patients were included in this study if they were followed up for more than 24 months postoperatively. All surgeries were performed by one of the authors (S.J.K.). Informed written consent for the surgical procedures was obtained from all patients and their parents.
Patients who had a history of prior strabismus surgery, simultaneous vertical and/or oblique muscle surgery, or vertical transposition of horizontal muscles during intermittent exotropia surgery, and/or other ocular abnormalities, were excluded. Patients were also excluded if they had paralytic or restrictive exotropia or a systemic anomaly, such as a neurologic disorder or a developmental delay. Patients with an A or V pattern, dissociated vertical deviation, or oblique muscle over-actions that did not require surgery were not excluded.
Medical records of patients were reviewed retrospectively and abstracted for age at onset of the deviation, age at the time of surgery, duration from onset of deviation to surgery, sex, best-corrected visual acuity (BCVA), refractive errors, and the type of surgery performed (BLR/RR). The presence of amblyopia and anisometropia was investigated. Preoperative deviation; presence of fixation preference and lateral incomitancy; postoperative deviations at postoperative day 1, months 1 and 6, and years 1 and 2, and every year post 2 years to the last examination; history of reoperation; and follow-up period were also collected. Amblyopia was defined as at least 2 Snellen lines difference in visual acuity between the eyes and anisometropia as difference of hyperopia >+1.50 diopters (D), myopia >−1.50 D, and/or astigmatism >+1.50 D. Basic-type exodeviation was defined to have the distance deviation, which is within 10 prism diopters (Δ) of the near deviation. Lateral incomitancy was defined as a condition in which the angle of exodeviation for lateral gaze was less than the angle for primary gaze by >10 Δ.
All patients underwent complete ophthalmologic examinations before surgery. Preoperative measurements of the angle of deviation were performed on at least 3 different occasions in all patients. The angle of deviation was determined primarily by the prism and alternate cover testing with accommodative targets for fixation both at a distance (6 m) and near (1/3 m) in primary and lateral gaze, with appropriate spectacle correction when required. A modified Krimsky method was used in examination of a few uncooperative patients. Part-time occlusion therapy was attempted in patients with a fixation preference or in those whose parents wanted to postpone surgical intervention.
All surgeries were performed under general anesthesia using the surgical formula based on the surgeon’s experience ( Table 1 ). Surgical dosage was based on the angle of distant deviation. The selection of surgical procedure was made by the operating surgeon, who had no preference for BLR or RR in basic-type exotropia. However, there was a tendency that BLR was performed in patients with large-angle (≥40 Δ) exotropia to avoid severe incomitance on horizontal gaze at early postoperative period, and RR in patients with dominant fixing eye. In moderate-angle (from 20 Δ to 40 Δ) exotropia without fixation preference, BLR or RR was performed after discussion about 1-eye vs 2-eye surgery with the patient and his or her parents.
| Prism Diopters | BLR (mm) | RR (rec/res, mm) |
|---|---|---|
| 15 | 4 | |
| 20 | 5 | 5/4 |
| 25 | 5.5 | 6/4 |
| 30 | 6 | 6/5 |
| 35 | 7 | 7/5 |
| 40 | 8 | 8/5 |
| 45 | 9 | 8/6 |
| 50 | 9.5 | 9/6 |
a The surgical doses used for treatment of intermittent exotropia in this study were based on the surgeon’s experience.
Postoperative measurements of distant and near deviations were performed at postoperative day 1 and following examinations in the same manner as that of preoperative measurement. Patients with diplopia associated with postoperative esotropia were managed by alternating full-time patching for 1 to 4 weeks until diplopia was resolved. If the esotropia did not show a reduction in 4 weeks, base-out prism glasses were prescribed to allow constant fusion until the esotropia was resolved. Reoperation for consecutive esotropia was performed if constant esotropia of ≥20 Δ persisted for more than 6 months postoperatively.
Surgical outcomes were divided into 3 categories: overcorrection (esophoria/tropia >5 Δ), success (esophoria/tropia ≤5 Δ to exophoria/tropia ≤10 Δ), and undercorrection/recurrence (exophoria/tropia >10 Δ) according to postoperative angle of deviation at distance. Duration from surgery to recurrence was examined. Reoperation for recurrent exotropia was performed when the maximal angle of deviation was at least 15 Δ of exotropia or more and patients had poor fusional control, in which an increase in the manifest phase of exotropia was noticed frequently by parents or clinicians.
An independent t test was used for comparison of patients’ demographic data and preoperative and postoperative angle of deviation between groups. A χ 2 test was used for comparison of surgical outcomes at each postoperative time and the final outcome. Kaplan-Meier survival analysis and a log-rank test were used for comparison of the recurrence rate. A logistic regression test was used for examination of the influence of surgical procedures on recurrence rate. Probability values of <0.05 were considered statistically significant. SPSS software for Windows (version 17.0; SPSS Inc, Chicago, Illinois, USA) was used for all analyses.
Results
One hundred twenty-eight patients were included in this study. Fifty-five patients, including 25 girls and 30 boys, underwent BLR and 73 patients, including 45 girls and 28 boys, underwent RR. The mean age of deviation onset of patients by parental report was 37.1 ± 38.1 months in the BLR group and 40.5 ± 28.2 months in the RR group. BCVA and refractive errors at the initial examination did not differ between the groups. The mean age at surgery was 81.8 ± 40.8 months in the BLR group and 86.5 ± 28.1 months in the RR group. The mean duration from onset of deviation to surgery was 43.9 ± 31.7 months in the BLR group and 46.0 ± 22.3 months in the RR group. The follow-up period after the initial surgery was 44.2 ± 15.8 months in the BLR group and 47.8 ± 16.9 months in the RR group. No statistically significant difference in mean age at surgery, mean duration from onset of deviation to surgery, and follow-up period were observed between the groups ( P > .05 in all comparisons, independent t test). However, patients’ mean preoperative angle of deviation was 40.5 ± 5.8 Δ at distance and 40.0 ± 8.0 Δ at near in the BLR group and 29.4 ± 3.8 Δ and 30.5 ± 6.4 Δ at each fixation distance in the RR group, which showed significant differences between the groups ( P < .01, independent t test) ( Table 2 ).
| BLR Group | RR Group | P Value | |
|---|---|---|---|
| No. of patients | 55 | 73 | |
| Sex, F:M | 25:30 | 45:28 | |
| Age at onset of deviation, mean (range), months | 37.1 ± 38.1 | 40.5 ± 28.2 | .57 a |
| Best-corrected visual acuity | |||
| OD, mean (range) | 20/25 (20/200∼20/13) | 20/25 (20/200∼20/13) | .89 a |
| OS, mean (range) | 20/25 (20/50∼20/13) | 20/25 (20/60∼20/13) | .67 a |
| Spherical equivalent, mean (range), diopters | |||
| OD, mean (range) | −0.82 ± 2.44 | −0.60 ± 1.65 | .55 a |
| OS, mean (range) | −0.71 ± 2.35 | −0.70 ± 1.57 | .57 a |
| Age at surgery, mean (range), months | 81.8 ± 40.8 | 86.5 ± 28.1 | .45 a |
| Duration from onset of deviation to surgery, mean (range), months | 43.9 ± 31.7 | 46.0 ± 22.3 | .67 a |
| Follow-up period, mean (range), months | 44.2 ± 15.8 | 47.8 ± 16.9 | .22 a |
| Preoperative angle of deviation, mean (range), prism diopters | |||
| At distance | 40.5 ± 5.8 | 29.4 ± 3.8 | <.01 a |
| At near | 40.0 ± 8.0 | 30.5 ± 6.4 | <.01 a |
| Amblyopia, no. of patients (%) | 4 (7.2%) | 5 (6.8%) | .93 b |
| Anisometropia, no. of patients (%) | 0 (0.0%) | 0 (0.0%) | |
| Fixation preference, no. of patients (%) | 5 (9.1%) | 19 (26.0%) | .02 b |
| Lateral incomitancy, no. of patients (%) | 2 (3.6%) | 5 (6.8%) | .46 b |
a P value by the independent t test.
Amblyopia was observed in 6 patients in both groups and anisometropia was not observed in either group. Patients with fixation preference were more common in the RR group than in the BLR group (19 of 73 patients [26.0%] vs 5 of 55 patients [9.1%], P = .03, χ 2 test). Lateral incomitancy was observed in 2 of 55 patients (3.6%) in the BLR group and 5 of 73 patients (6.8%) in the RR group ( Table 2 ).
Mean postoperative deviations at distant and near fixation did not differ between the groups on postoperative day 1. However, at postoperative month 1, deviation at distance was more exotropic in the BLR group than in the RR group ( P = .03, independent t test). After that, deviations became more exotropic in the RR than in the BLR group, with a statistical significance at postoperative year 2 ( P = .04, independent t test). Deviations at near also were more exotropic in the RR group than in the BLR group, showing statistically significant differences at postoperative year 1 ( P = .01, independent t test). On the last examination, there were no differences of the mean angle of deviation at both distance and near between the groups after some recurrent cases underwent reoperations ( Table 3 and Figure 1 ) . Proportions of surgical results at each postoperative time in each group demonstrated that proportions of overcorrection showed a decrease and proportions of recurrence showed an increase in each group with passage of time after surgery. Surgical outcomes at each postoperative time by 2 years after surgery were not different between the groups ( P > .05, χ 2 test); however, the final outcome of the first procedure differed significantly between the groups, demonstrating a higher success rate in the BLR group than in the RR group (32/55 patients [58.2%] vs 20/73 patients [27.4%], P < .01, χ 2 test) ( Table 4 and Figure 2 ) . The main cause of surgical failure was recurrence, which occurred in 21 of 55 patients (38.2%) in the BLR group and 50 of 73 patients (68.5%) in the RR group.
| Angle of Deviation at Distance (at Near), Mean ± SD (Range), Prism Diopters a | |||
|---|---|---|---|
| Time After Surgery | BLR Group | RR Group | P Value b |
| 1 day | −6.64 ± 7.07 (−5.21 ± 8.28) | −8.12 ± 6.39 (−5.77 ± 7.58) | .22 (.75) |
| 1 month | 4.22 ± 7.63 (3.13 ± 8.32) | 1.53 ± 5.98 (1.81 ± 7.22) | .03 (.34) |
| 6 months | 2.67 ± 8.71 (2.17 ± 9.92) | 4.63 ± 8.85 (5.45 ± 10.22) | .22 (.07) |
| 1 year | 3.60 ± 8.68 (3.56 ± 9.26) | 6.83 ± 9.88 (8.47 ± 11.16) | .06 (.01) |
| 2 years | 6.13 ± 8.71 (7.39 ± 10.62) | 9.31 ± 8.78 (11.04 ± 10.36) | .04 (.06) |
| Last examination | 7.33 ± 9.15 (8.16 ± 9.91) | 8.88 ± 8.81 (8.81 ± 9.71) | .33 (.72) |
a The mean deviations at each postoperative time were calculated, including the angles of patients who underwent further operations.
| Time After Surgery | Surgical Outcome at Distance a | BLR Group No. of Patients (%) | RR Group No. of Patients (%) | P Value b |
|---|---|---|---|---|
| 1 day |
|
|
| .12 |
| 1 month |
|
|
| .41 |
| 6 months |
|
|
| .70 |
| 1 year |
|
|
| .38 |
| 2 years |
|
|
| .23 |
| Final surgical outcome c |
|
|
| <.01 |
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