Purpose
To compare the surgical outcomes of unilateral lateral rectus recession–medial rectus resection (RR) and unilateral lateral rectus recession (ULR) for intermittent exotropia of ≤20 prism diopters (PD).
Design
Retrospective, nonrandomized clinical study.
Methods
A total of 130 children with intermittent exotropia of ≤20 PD who underwent unilateral RR or ULR of 10 mm were included. Patients were observed for at least 2 years. Success rates, cumulative probabilities of success, and factors related to recurrence and overcorrection were evaluated.
Results
The mean follow-up duration after surgery was 3.1 ± 1.0 years in the RR group and 3.6 ± 1.6 years in the ULR group. In the RR group, 38 of 61 patients (62%) had ocular alignment within 10 PD of exophoria/tropia and 5 PD of esophoria/tropia; 18 patients (30%) had recurrence, and 5 (8%) had overcorrection. In the ULR group, 26 of 69 patients (38%) had successful alignment, 41 patients (59%) had recurrence, and 2 patients (3%) were overcorrected. At 6 months after surgery, the success rate was significantly higher in the ULR group (RR 61%; ULR 78%, P = .039), but it became comparable after 2 years (RR 60%; ULR 52%, P = .370). At the final examination after a mean duration of 3 years, the recurrence rates were lower in the RR group (30% vs 59%, P = .001), and the overcorrection rates were comparable (8% vs 3%, P = .252).
Conclusion
Unilateral RR resulted in more successful alignment and lower recurrence compared to ULR for the treatment of small-angle intermittent exotropia of ≤20 PD.
In children with small-angle intermittent exotropia of ≤20 prism diopters (PD), making decisions to perform strabismus surgery and choosing the optimal surgical procedure may not be easy. In previous reports, unilateral lateral rectus recession (ULR) has been frequently performed for small-angle exotropia, and the reported rate of successful outcomes varied widely from 36% to 84%.
There are several advantages of operating on 1 muscle instead of 2, such as shortening the anesthesia time, reducing the risks associated with muscle surgery, and saving other rectus muscles for reoperation. Under these advantages, ULR has been described as a surgical option for moderate-angle exotropia since 1950. However, the majority of studies regarding ULR have investigated the efficacy of ULR alone in patients with variable ranges of exodeviation. Comparisons of success rates between different surgical methods were performed mostly between ULR and bilateral lateral rectus recession (BLR), and there was only 1 recent study that compared ULR and unilateral recess-resect procedure (RR) for the treatment of moderate-angle intermittent exotropia of 20–25 PD, showing similar results between both methods up to 2 years. However, comparison of long-term success rates for patients, particularly with small-angle exotropia of ≤20 PD, between different surgical methods has not been well established.
In this study, a retrospective review was conducted to compare the long-term surgical outcomes between RR and ULR for the treatment of small-angle intermittent exotropia of ≤20 PD, with a minimum follow-up period of 2 years.
Methods
A retrospective review of medical records was performed on 130 consecutive patients who underwent surgery for intermittent exotropia ≤20 PD by 1 surgeon (J.-M.H.) between 2008 and 2013. Seventy-four patients were included from our previous retrospective study of exotropia under 25 PD treated by ULR. The minimum required follow-up period after surgery was 24 months, unless the patient underwent reoperation for recurrence prior to 24 months. Cases involving patients younger than 3 years of age at the time of surgery, convergence insufficiency type exotropia, histories of strabismus surgery, moderate to severe amblyopia, paralytic or restrictive strabismus, ocular disease other than strabismus, congenital anomalies, and neurologic disorders were excluded from our study. Patients with dissociated vertical deviation, A or V patterns, or oblique muscle overactions not requiring surgery were included. This study adhered to the Declaration of Helsinki, and the protocol was approved by the Institutional Review Board of Seoul National University Bundang Hospital.
Preoperative Ophthalmologic Examination
A prism and alternate cover testing with accommodative targets for fixation at 1/3 m and 6 m was performed. An additional near measurement was obtained after 1 hour of monocular occlusion of the habitually deviating eye, and another postocclusion near measurement was obtained with an additional +3.00 diopters (D) sphere over each eye prior to allowing the patient to regain binocular fusion. In patients with hyperopia, glasses of approximately 1.00–1.50 D less than the full cycloplegic hyperopic refraction were given. We noted preoperative patient characteristics, including sex, age at surgery, deviation at distance and near, fixation dominance, presence of lateral incomitance, stereopsis, refractive errors, presence of amblyopia, anisometropia, A or V pattern, dissociated vertical deviation, vertical deviation, and superior oblique or inferior oblique overaction. The presence of fixation dominance was determined with repeated examinations of the cover-uncover test. Lateral incomitance was defined as ≥5 PD change in right or left gaze from the primary position. Refractive errors were determined using cycloplegic refraction with cyclopentolate hydrochloride 1% and analyzed as spherical equivalent values. Anisometropia was defined as a spherical or cylindrical difference of >1.50 D between the 2 eyes. Amblyopia was defined as a difference of 2 lines or more between monocular visual acuities, and only mild amblyopia with a difference of 2 lines but best-corrected visual acuity of the worse eye ≥20/40 were included. An A pattern was defined as an increase of ≥10 PD of exodeviation at down gaze compared with up gaze, and V pattern was defined as an increase of ≥15 PD of exodeviation at up gaze compared with down gaze. Stereoacuity of ≤100 seconds of arc (arcsec) with the Randot stereoacuity test (StereoOptical Co, Inc, Chicago, Illinois, USA) was defined as good.
Intraoperative Procedures
All surgeries were performed under general anesthesia by 1 surgeon (J.-M.H.). The selection of surgical procedure was made by the operating surgeon. One of the following procedures was performed: (1) unilateral MR resection based on the near deviation, with LR recession based on the distant deviation (RR); or (2) unilateral 10.0 mm LR recession (ULR). The surgical table is presented in Table 1 .
| Deviation (PD) | LR Recession/MR Resection (mm) | Unilateral LR Recession (mm) | |
|---|---|---|---|
| ≤15 | 3.5 | 3 | 10 |
| 16 | 4 | 3 | 10 |
| 18 | 4.5 | 3.5 | 10 |
| 20 | 5 | 4 | 10 |
Postoperative Measurements
Postoperative alignment at distance in the primary position was measured at 1, 6, 12, and 24 months postoperatively and afterward. Patients with diplopia associated with postoperative esotropia were managed with alternating full-time patching for 1–4 weeks until diplopia resolved. If the esotropia did not improve to the point that the patient could comfortably fuse in 4 weeks, cycloplegic refraction was performed again, and hyperopia >+1.00 D was corrected. Patients without hyperopia of +1.00 D were prescribed base-out Fresnel press-on prisms (3M Health Care, St Paul, Minnesota, USA) to facilitate constant fusion. When it became evident that prisms would have to be worn for several months, prisms incorporated into regular spectacles were prescribed. An outcome was considered successful if the distant deviation in the primary position was between ≤10 PD of exophoria/tropia and ≤5 PD of esophoria/tropia. Recurrence was defined as an alignment of >10 PD of exophoria/tropia, and overcorrection was defined as >5 PD of esotropia. Reoperation for overcorrected patients was performed if esotropia of >20 PD persisted or increased for 6 months after surgery. Reoperation for recurrent or residual exotropia was recommended for constant exotropia ≥14 PD at distance, despite treatment by nonsurgical means, such as part-time occlusion or minus-lens therapy in most patients. Improved stereopsis was defined as a decrease of ≥2 octaves at the last follow-up examination or before reoperation, and decreased stereopsis was defined as an increase of ≥2 octaves.
Main Outcome Measures
Primary outcome measures included cumulative probabilities of success at 2 years after surgery and long-term surgical success rates based on postoperative alignment at distance, improvement in stereopsis, rates of recurrence, and overcorrection.
Statistical Analysis
Statistical analyses were performed using SPSS for Windows v 22.0 (SPSS, Chicago, Illinois, USA). The independent t test, χ 2 test, Fisher exact test, and Mann-Whitney U test were used to compare the patients’ characteristics and the surgical outcomes. Cumulative probabilities of success were assessed according to the Kaplan-Meier life-table analysis. The risk factors associated with recurrence and overcorrection after operation including sex, age of onset, age at surgery, periods of follow-up, duration of deviation, refractive errors, best-corrected visual acuity, preoperative deviation, type of exotropia, surgical results at 1 month after surgery, existence of familial history of exotropia, constant deviation at distant fixation, hypertropia over 5 PD, dissociated vertical deviation (DVD), A or V pattern, oblique muscle dysfunction, lateral incomitance, fixation preference, and preoperative stereoscopic status were estimated using univariate and multivariate logistic regression analyses. P < .05 was considered statistically significant.
Results
Patient Demographics
A total of 130 patients were included in this study. Sixty-one patients (27 female) underwent RR and 69 patients (40 female) underwent ULR. The preoperative patient characteristics were not significantly different in the 2 groups ( Table 2 ).
| Variable | RR (N = 61) | ULR (N = 69) | P Value |
|---|---|---|---|
| Sex (M:F) | 34:27 | 29:40 | .119 a |
| Age of onset (y) | 5.0 ± 2.7 | 5.0 ± 2.7 | .591 b |
| Age at surgery (y) | 7.0 ± 2.5 | 7.0 ± 2.3 | .938 b |
| Period of follow-up (y) | 3.1 ± 1.0 | 3.6 ± 1.6 | .103 d |
| Duration of deviation (y) | 2.0 ± 2.1 | 2.2 ± 2.1 | .600 b |
| Refractive errors (SE, diopters) | −0.4 ± 1.5 | −0.2 ± 1.7 | .255 b |
| Best-corrected visual acuity | |||
| OD, mean (range) | 20/23 (20/40–20/16) | 20/22 (20/40–20/13) | .275 a |
| OS, mean (range) | 20/23 (20/40–20/16) | 20/22 (20/40–20/13) | .203 a |
| Follow-up to recurrence | 36.4 ± 12.1 (12–72) | 38.2 ± 22.6 (1.2–84) | .556 b |
| Follow-up to reoperation | 27.1 ± 11.3 (12–47) | 34.8 ± 15.0 (15–66) | .108 b |
| Preoperative deviation | |||
| Maximum (PD) | 19.4 ± 0.9 | 19.6 ± 0.9 | .339 b |
| Distance (PD) | 18.7 ± 2.5 | 19.2 ± 1.4 | .134 b |
| Near (PD) | 18.3 ± 2.3 | 17.7 ± 2.7 | .508 b |
| Distance – Near (PD) | 0.4 ± 3.2 | 1.5 ± 3.1 | .055 d |
| Family history | 7/60 (11.7%) | 11/64 (17.2%) | .383 a |
| Type of exodeviation | |||
| Basic | 61 (100.0%) | 67 (97.1%) | .498 c |
| Divergence excess | 0 (0.0%) | 2 (2.9%) | |
| Constant deviation | |||
| Distance | 33 (54.1%) | 40 (58.0%) | .657 a |
| Near | 16 (26.2%) | 16 (23.2%) | .688 a |
| Associated features | |||
| Hypertropia over 5 PD | 4 (6.6%) | 3 (4.3%) | .707 c |
| DVD | 0 (0.0%) | 2 (2.8%) | .498 c |
| A or V pattern | 0 (0.0%) | 1 (1.4%) | >0.999 c |
| IO overaction | 12 (19.7%) | 14 (20.3%) | .930 a |
| SO overaction | 2 (3.3%) | 4 (5.8%) | .684 c |
| Lateral incomitance | 1 (1.6%) | 1 (1.4%) | >0.999 c |
| Amblyopia | 5 (8.2%) | 2 (2.9%) | .252 c |
| Anisometropia | 6 (9.8%) | 4 (5.8%) | .514 c |
| Fixation preference | 35 (57.4%) | 36 (52.2%) | .552 a |
| Good stereopsis | 37/57 (60.7%) | 51/69 (73.9%) | .273 a |
Surgical Outcomes
In the examination at their last visit after a mean follow-up of 3.1 years, 38 of 61 patients (62%) in the RR group had ocular alignment meeting the defined criteria of success, 18 patients (30%) had recurrence, and 5 patients (8%) had overcorrection. In the ULR group, 26 of 69 patients (38%) had successful alignment, 41 patients (59%) had recurrence, and 2 patients (3%) were overcorrected ( Table 3 ).
| Successful Alignment | Recurrence | Overcorrection | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 M | 6 M | 1 Y | 2 Y | Final | 1 M | 6 M | 1 Y | 2 Y | Final | 1 M | 6 M | 1 Y | 2 Y | Final | |
| RR, n (%) | 37 (61) | 36 (61) | 38 (64) | 35 (60) | 38 (62) | 0 (0) | 3 (5) | 4 (7) | 12 (21) | 18 (30) | 24 (39) | 20 (34) | 17 (29) | 11 (19) | 5 (8) |
| ULR, n (%) | 59 (86) | 50 (78) | 48 (72) | 34 (52) | 26 (38) | 6 (9) | 11 (17) | 16 (24) | 28 (43) | 41 (59) | 4 (6) | 3 (5) | 3 (5) | 3 (5) | 2 (3) |
| P value | <0.001 a | .039 a | .384 a | .370 a | .005 a | .029 b | .035 a | .009 a | .008 a | .001 a | <0.001 a | <0.001 a | <0.001 a | .012 a | .252 b |
Until 6 months after surgery, the success rate was significantly higher in the ULR group (RR 61% vs ULR 78%, P = .039); however, it became comparable after 1 year and reversed at the final examination. The final success rate was higher in the RR group (62% vs 38%, P = .005). The recurrence rates were higher in the ULR group during all follow-up periods up to 2 years (21% vs 43%, P = .008) and final examination (30% vs 59%, P = .001). The overcorrection rate was higher in the RR group until 2 years after operation (19% vs 5%, P = .012); however, it became comparable at the final examination (8% vs 3%, P = .252) ( Table 2 ).
Surgical outcomes according to the magnitude of preoperative deviation at the final examination are summarized in Figure 1 . In patients with an exodeviation of <20 PD, the rates of achieving successful alignment were similar in the RR and ULR groups ( P = .241). However, in patients with an exodeviation of 20 PD, the RR group (58.5%) showed higher rates of successful alignment than did the ULR group (35.1%) at the final examination ( P = .021).
