Purpose
To compare the long-term surgical outcomes of augmented bilateral lateral rectus (LR) recession with original surgery.
Design
Retrospective, nonrandomized clinical study.
Methods
A total of 447 children with ≤35 prism diopters (PD) of basic and divergence excess-type intermittent exotropia, who underwent original bilateral LR recession based on the largest angle measured at distance and near, or augmentation surgery with the surgical dosage augmented by 1.0–1.5 mm more than the original formula were included. Patients were observed for at least 2 years. Success rates, cumulative probabilities of success, factors related to recurrence, and overcorrection were evaluated.
Results
At a mean follow-up of 4.0 years, 48 of 101 patients (48%) undergoing original surgery maintained successful alignment within 10 PD of exophoria/tropia and 5 PD of esophoria/tropia; 49 (49%) had recurrence, and 3 (3%) had overcorrection. After augmented surgery, 203 of 346 patients (59%) were successfully aligned, 129 (37%) had recurrence, and 14 (4%) had overcorrection. Augmented surgery showed higher long-term successful alignment rates ( P = .047) and lower recurrence rates compared to original surgery ( P = .042) and the overcorrection rate was similar between the 2 groups ( P = .774). Patients with divergence excess type showed higher cumulative success rates compared to that of the basic type ( P = .010) after augmented surgery.
Conclusion
Augmented bilateral LR recession resulted in more successful alignment and lower recurrence without higher overcorrection compared to the original surgery for the children with intermittent exotropia. Augmentation of the original table should be considered when planning bilateral LR recession, especially in patients with divergence excess–type exotropia.
Exotropic drift is common after surgery for exotropia, resulting in recurrence over time in many patients. Reported success rates after bilateral lateral rectus (LR) recession in intermittent exotropia are highly variable, ranging from 41% to 83%. This variability comes from the various lengths of follow-up periods among the studies that were reflected by the increasing rate of recurrence as time passes.
Kushner suggested that increasing the amount of bilateral LR recession might be beneficial for patients with basic-type intermittent exotropia. Mims and Wood reported that they routinely added up to 1.0 mm as the near deviation approached the distance deviation in size. Since Lee and associates first reported better surgical success rates with the augmented bilateral LR recession in exotropia, there have been 2 more studies. However, these studies included a small number of patients and the follow-up duration was short. Furthermore, the previous studies only included basic-type exotropia and no study compared surgical outcomes of augmented surgery according to type of exotropia.
In this study, we evaluated the long-term outcomes of augmented bilateral LR recession in a large number of subjects with intermittent exotropia who were followed up for more than 2 years. Our goal was to determine whether augmented amounts of the recessed muscle could play a role in the long-term stability of exotropia by reducing the rate of late recurrence. In addition, surgical outcomes of original and augmented surgery were compared between different types of exotropia.
Methods
A retrospective review of medical records was performed on 447 consecutive patients who underwent surgery for intermittent exotropia ≤35 prism diopters (PD) by 1 surgeon (J.-M.H.) between 1997 and 2013. The minimum required follow-up period after surgery was 24 months, except for patients who required reoperation within 24 months after the primary surgery. Patients younger than 3 years of age at the time of surgery or patients who had convergence insufficiency–type exotropia, histories of strabismus surgery, moderate to severe amblyopia, paralytic or restrictive strabismus, ocular disease other than strabismus, congenital anomalies, or neurologic disorders were excluded from our study. Patients with A or V patterns, dissociated vertical deviation, or oblique muscle overactions that did not require 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 test with accommodative targets for fixation at 0.3 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 with the 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 or arc (arcsec) with the Randot stereoacuity test was defined as good.
Intraoperative Procedures
All surgeries were performed under general anesthesia by 1 surgeon (J.-M.H.). Original bilateral LR recession was performed according to the Wright formula based on the largest angle of deviation measured during distance and near fixation. Augmentation surgery was performed in patients with the surgical dosage augmented by 1.0–1.5 mm over the original formula. The surgical table is presented in Table 1 .
| Deviation (PD) | Original Surgery OU (mm) | Augmented Surgery OU (mm) | |
|---|---|---|---|
| 20 | 5 | 6 | 6.5 |
| 25 | 6 | 7 | 7.5 |
| 30 | 7 | 8 | 8.5 |
| 35 | 7.5 | 8.5 | 9 |
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 reduce with alternate patching for 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 a number of months, prisms incorporated into regular spectacles were prescribed. An outcome was considered satisfactory 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 exotropia, 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.
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. Subgroup analysis was performed according to the type of exotropia.
Statistical Analysis
Statistical analyses were performed using SPSS for Windows v 22.0 (SPSS, Chicago, Illinois, USA). The independent t test, χ 2 test, and Fisher exact test were used to compare the patient’s characteristics and the surgical outcomes. Cumulative probabilities of success were assessed according to the Kaplan-Meier life-table analysis. Correlations between outcomes at each follow-up period were examined with McNemar-Bowker test and generalized estimating equation. The risk factors associated with recurrence and overcorrection after operation including age of onset, age at surgery, type of exotropia, sex, amount of preoperative exodeviation, refractive errors, type of surgery, surgical results at 1 month after surgery, and existence of 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 analyses. P < .05 was considered statistically significant.
Results
Patient Demographics
Among the 447 patients, 101 patients underwent original surgery and 346 patients received augmented surgery. The preoperative patient characteristics were not significantly different in the 2 groups except for the type of exodeviation and DVD ( Table 2 ).
| Variable | Original (N = 101) | Augmentation (N = 346) | P Value |
|---|---|---|---|
| Sex (M:F) | 51:50 | 145:201 | .126 a |
| Age of onset (y) | 3.3 ± 2.4 | 3.6 ± 2.5 | .321 b |
| Age at surgery (y) | 6.9 ± 4.8 | 7.2 ± 3.3 | .491 b |
| Period of follow-up (y) | 4.1 ± 2.8 | 4.0 ± 2.0 | .572 b |
| Duration of deviation (y) | 3.7 ± 3.4 | 3.6 ± 3.1 | .960 b |
| Refractive errors (SE, diopters) | −0.4 ± 1.5 | −0.2 ± 1.7 | .255 b |
| Preoperative deviation | |||
| Maximum (PD) | 29.6 ± 5.3 | 29.2 ± 4.3 | .511 b |
| Distance (PD) | 28.4 ± 6.1 | 28.2 ± 4.4 | .720 b |
| Near (PD) | 24.6 ± 7.5 | 26.0 ± 6.1 | .106 b |
| Distance – near (PD) | 4.1 ± 7.3 | 2.2 ± 5.7 | .016 b |
| Type of exodeviation | |||
| Basic (+simulated DE) | 74 (73.3%) | 297 (85.8%) | .003 a |
| Divergence excess | 27 (26.7%) | 49 (14.2%) | |
| Associated features | |||
| Hypertropia over 5 PD | 7 (6.9%) | 22 (6.4%) | .837 a |
| DVD | 5 (7.0%) | 3 (0.9%) | .001 a |
| A or V pattern | 0 (0.0%) | 4 (1.2%) | .278 a |
| IO overaction | 8 (7.9%) | 29 (8.4%) | .882 a |
| SO overaction | 3 (3.0%) | 2 (0.6%) | .079 c |
| Lateral incomitance | 1/60 (1.0%) | 31/346 (9.0%) | .053 b |
| Fixation preference | 31 (30.7%) | 113 (32.7%) | .710 b |
| Good stereopsis | 47/75 (62.7%) | 210/294 (71.4%) | .141 b |
Surgical Outcomes
At the final examination after a mean follow-up of 4.0 years, 48 of 101 patients (48%) in the original group had ocular alignment meeting the defined criteria of success, 49 patients (49%) had recurrence, and 3 patients (4%) had overcorrection ( Table 3 ). In the augmented group, 203 of 346 patients (59%) had successful alignment, 129 patients (37%) had recurrence, and 14 patients (4%) were overcorrected.
| 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 | |
| Original (n, %) | 78 (77) | 60 (61) | 47 (51) | 45 (52) | 48 (48) | 13 (13) | 32 (33) | 38 (41) | 37 (43) | 50 (49) | 10 (10) | 6 (6) | 7 (8) | 5 (6) | 3 (3) |
| Augmentation (n, %) | 245 (71) | 199 (77) | 222 (77) | 193 (64) | 203 (59) | 34 (9.8) | 37 (14) | 43 (15) | 80 (27) | 129 (37) | 67 (19) | 23 (9) | 25 (10) | 28 (10) | 14 (4) |
| P value a | .205 | .003 | .000 | .037 | .047 | .380 | .000 | .000 | .004 | .042 | .027 | .395 | .760 | .295 | .774 |
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