Factors Associated with Surgical Outcomes of Intermittent Exotropia in Children

doi:10.21203/rs.3.rs-3247040/v1

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Factors Associated with Surgical Outcomes of Intermittent Exotropia in Children

https://doi.org/10.21203/rs.3.rs-3247040/v1

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Purpose

To evaluate factors associated with surgical outcomes of children with intermittent exotropia (IXT).

Methods

A retrospective study was performed for 125 patients who had undergone intermittent exotropia surgery with at least one year of follow up. Surgical outcomes were grouped as success (esophoria/tropia ≤ 5 prism diopers (PD) to exophoria/tropia ≤ 10 PD), failure (esophoria/tropia > 5PD or exophoria/tropia > 10PD) according to the angle of deviation at postoperative one year. We investigated subjects’ clinical and demographic factors including magnitude of exo-deviation, stereoacuity at near and distance, and response to patching at 3 months after patching. Factors associated with surgical outcomes were then determined through univariate and multivariate analyses.

Results

Of a total of 125 patients, 102 (81.6%) were assigned to the success group and 23 (18.4%) to the failure group. Univariate analysis revealed that absence of anisometropia, smaller preoperative near exodeviation, better stereopsis at near, magnitude of deviation at postoperative day 1, and good response to preoperative patching were significantly associated with surgical success for IXT at postoperative one year. In multivariate analysis, distant esotropic magnitude of deviation at postoperative day 1 was the only factor affecting successful surgical outcome.

Conclusions

Preoperative patching and small distant esotropia at postoperative day 1 are prognostic factors that could be altered in an effort to provide a successful surgical outcome.

Health sciences/Diseases/Eye diseases/Ocular motility disorders

Health sciences/Diseases/Eye diseases/Eye abnormalities

Intermittent exotropia

Part-time patching

Surgical outcomes

Intermittent exotropia (IXT) is characterized by periods of normal binocular alignment with sensory fusion and a manifest exotropia alternatively.^1–3 The optimal method for treating IXT has not yet been established, with both surgical and nonsurgical treatment options prescribed commonly.^4.5 The purpose of treatment is to improve alignment and control of both eyes, thereby preserving stereoacuity and visual acuity.

Surgical treatment has the advantage of immediate effect. However, it has limitations in cost and risk of complications including recurrence and overcorrection which can also induce defects of fusion and stereopsis. Indications to perform surgery include age of patient, angle of deviation, symptoms, fusion potential, history, onset, and prognosis.

There have been many studies on recurrence after surgery for exotropia. As the success rate of surgery varies by studies (32.8–83.3%),^6–8 exact prediction of surgical outcome is difficult. Numerous studies have suggested various factors possibly related to surgical success, including age at onset, timing of surgery,^9–11 preoperative angle of deviation,^7,12,13 visual acuity, and stereopsis.¹⁴ However, studies investigated whether preoperative patching is effective in maintaining successful outcome after surgery for IXT have not been reported yet.

Thus, the aim of this study was to determine clinical features including response to the preoperative patching associated with surgical outcomes of IXT patients at postoperative one year.

Numbers of male and female patients were 55 (44.0%) and 70 (56.0%), respectively. Mean age was 5.7 ± 3.5 years at diagnosis and 7.5 ± 3.0 years at surgery. Exotropia type was basic in 106 (84.8%) patients, DE type in 1 (0.8%), Pseudo-DE type in 14 (11.2%), and CI type in 4 (3.2%). Sixty-six (52.8%) patients showed good response to the preoperative patching treatment at 3-month visit from baseline (Table 1).

Table 1

Demographics of exotropia patients
Variables
Gender (M:F)	55:70
Age at diagnosis, mean ± SD (years)	5.7 ± 3.5
Age at operation, mean ± SD (years)	7.5 ± 3.0
Time from diagnosis to surgery, mean ± SD (years)	1.7 ± 2.0
Best corrected visual acuity (logMAR)
OD, mean ± SD	0.03 ± 0.12
OS, mean ± SD	0.04 ± 0.12
Refractive errors in right eye, mean ± SD (Diopters)
Spherical	-0.19 ± 1.48
Cylinder	-0.75 ± 0.88
Spherical equivalent, SE	-0.56 ± 1.52
Refractive errors in left eye, mean ± SD (Diopters)
Spherical	-0.13 ± 1.40
Cylinder	-1.20 ± 4.49
Spherical equivalent, SE	-0.73 ± 2.77
Anisometropia, n(%)	12 (9.6)
Type of exotropia, n (%)
Basic	106 (84.8)
Divergence excess	1 (0.8)
Pseudodivergence excess	14 (11.2)
Convergence insufficiency	4 (3.2)
Stereopsis at near (logarcsec)
Titmus stereo test	2.2 ± 0.6
Randot stereo test	1.9 ± 0.3
Stereopsis at distant
Distance Randot stereo test	2.2 ± 0.3
Worth 4 dot
Suppression, n (%)	41 (37.27)
Alternate fixation, n (%)	14 (12.72)
Preoperative patching
Good response, n (%)	66 (52.8)
Preoperative magnitude of deviation (PD)
At distance, mean ± SD	29.7 ± 8.5
At near, mean ± SD	28.5 ± 10.5
Postoperative deviation on day 1 (PD)
At distance, mean ± SD	-6.7 ± 6.4
At near, mean ± SD	-3.6 ± 6.0

Among the 125 patients, 102 belonged to the success group and 23 belonged to the failure group. The overall success rate was 81.6%. There was no statistical difference in sex, age at diagnosis, age at surgery, time from diagnosis to surgery, BCVA, refractive errors, or type of exotropia. There were more anisometropia (p = 0.04) and larger exodeviation at near (p = 0.04) in the failure group. The number of patients who had good response to the preoperative patching was greater (p = 0.04), good stereopsis at near (p = 0.05) and esotropic deviation at distance and near on postoperative 1 day was more (p < 0.001) in the success group than in the failure group (Table 2).

Table 2

Demographics of exotropia patients: analysis for association with surgical outcomes
	Success group (n = 102)	Failure group (n = 23)	p-value
Gender (M:F)	43:59	12:11	0.38^*
Age at diagnosis, m ± SD (years)	5.6 ± 3.2	6.2 ± 4.9	0.59^†
Age at surgery, m ± SD (years)	7.3 ± 2.6	8.4 ± 4.3	0.21^†
Time from diagnosis to surgery, m ± SD (years)	1.6 ± 2.0	2.2 ± 1.9	0.34^†
BCVA (logMAR)
OD, mean ± SD	0.03 ± 0.12	0.02 ± 0.11	0.535^†
OS, mean ± SD	0.04 ± 0.11	0.04 ± 0.14	0.904^†
Refractive errors in right eye, mean ± SD (Diopters)
Spherical	-0.18 ± 1.55	-0.22 ± 1.15	0.907
Cylinder	-0.67 ± 0.79	-1.11 ± 1.16	0.094
Spherical equivalent, SE	-0.52 ± 1.58	-0.78 ± 1.27	0.461
Refractive errors in left eye, mean ± SD (Diopters)
Spherical	-0.18 ± 1.47	0.10 ± 1.03	0.370
Cylinder	-1.25 ± 4.95	-0.99 ± 1.05	0.804
Spherical equivalent, SE	-0.81 ± 3.02	-0.39 ± 1.12	0.513
Anisometropia, n (%)	7	5	0.04^*
Type of exotropia			0.38^*
Basic	87	19
Divergence excess	1	0
Pseudodivergence excess	12	2
Convergence insufficiency	2	2
Stereopsis at near (logarcsec)
Titmus stereo test	2.1 ± 0.5	2.4 ± 0.8	0.05^†
Randot stereo test	1.9 ± 0.3	2.0 ± 0.3	0.59^†
Stereopsis at distant
Distance Randot stereo test	2.2 ± 0.3	2.3 ± 0.4	0.98
Worth 4 dot
Suppression, n (%)	31	9	0.62^*
Alternate fixation, n (%)	10	4
Preoperative magnitude of deviation (PD)
At distance, mean ± SD	29.2 ± 8.0	32.0 ± 10.3	0.15^†
At near, mean ± SD	27.4 ± 9.8	33.1 ± 12.6	0.04^†
Postoperative deviation on day 1 (PD)
At distance, mean ± SD	-8.3 ± 5.0	0.3 ± 7.3	< 0.001
At near, mean ± SD	-4.7 ± 5.4	1.6 ± 5.7	< 0.001
Preoperative patching			0.04^*
Good response to patching	53	13	0.04^*

Absence of anisometropia (odds ratio [OR], 3.77; p = 0.038), smaller exodeviation at near (OR, 0.95; p = 0.036), good titmus stereotest (OR, 0.47; p = 0.049), good response to patching (OR, 2.91; p = 0.037), and esotropic deviation at postoperative 1 day (OR, 0.778, p < 0.001 at distance; OR, 0.920, p < 0.001 at near) were significantly associated with successful outcome at postoperative 1 year by univariate analyses. Multivariate analysis revealed that patients with mild esotropic deviation at postoperative 1 day (OR, 0.792; p = 0.034) had successful surgical outcomes (Table 3).

Table 3

Logistic regression analysis for predicting intermittent exotropia recurrence
Variable	Univariate Analysis			Multivariate Analysis
Variable	OR	95% CI	p-value	OR	95% CI	p-value
Gender (Female)	0.668	0.270–1.656	0.384
Age at diagnosis	0.956	0.847–1.079	0.466
Age at operation	0.889	0.774–1.020	0.092	1.300	0.947–1.784	0.105
Time from diagnosis to surgery	0.876	0.150–1.073	0.200	0.935	0.672-1.300	0.688
BCVA(logMAR)
OD	3.551	0.067-188.829	0.532
OS	1.282	0.024–69.215	0.903
Absence of anisometropia	3.770	1.076–13.202	0.038	14.729	1.112-195.032	0.074
Type of exotropia			0.498
Basic
Psseudodivergence excess	0.763	0.158–3.694	0.737
Convergence insufficiency	0.167	0.014–1.963	0.154
Stereopsis at near
Titmus stereotest	0.471	0.223–0.996	0.049	0.998	0.268–3.718	0.997
Randot stereo test	0.981	0.149–6.453	0.984	6.055	0.231-158.387	0.280
Stereopsis at distant
Distance Randot stereo test	0.974	0.154–6.160	0.978
Preoperative magnitude of deviation (PD)
At distance, mean ± SD	0.964	0.915–1.015	0.159	0.913	0.794–1.049	0.198
At near, mean ± SD	0.951	0.909–0.994	0.036	1.000	0.9896–1.116	0.995
Postoperative deviation on day 1 (PD)
At distance, mean ± SD	0.778	0.699–0.867	< 0.001	0.792	0.639–0.983	0.034
At near, mean ± SD	0.920	0.704–0.891	< 0.001	0.900	0.702–1.153	0.406
Response to patching (Good)	2.908	1.013–8.348	0.037	5.317	0.824–34.325	0.079
Conceptualization: K.S.J.; study design: K.S.J.; data collection: K.S.Y. and Y.S.A; data and statistical analyses: Y.S.A.; drafting the manuscript: K.S.J. and Y.S.A.; manuscript revision: C.H.Y. and L.J.E. All authors have read and agreed to the published version of the manuscript.

This study analyzed surgical outcomes of 125 children diagnosed with IXT. Successful surgical outcome defined as esotropia of less than 5 PD or exotropia of less than 10 PD was accomplished in 81.6% of children after 1 year of follow-up. Although direct comparison is difficult due to differences in specific parameters and criteria used in each study, success rates have been reported to be around 32.8–83.3% when compared with studies of similar standards.^6–8,15 Generally, studies with shorter periods of follow-up reported higher rates of success than those with longer follow-up periods. Since this study measured surgical outcome at postoperative 1 year, the success rate was expected to be relatively higher than other studies.

To date, factors possibly influencing surgical outcomes have been well studied. In our study, it was found that absence of anisometropia, preoperative smaller exodeviation at near, mild esotropic deviation at postoperative day 1, and good response to patching were associated with surgical success in patients with IXT.

Kim & Choi ¹⁶ have conducted a study analyzing patients with IXT observed for more than 2 years after surgery and reported that surgical outcome for IXT is statistically significant in angle of deviation at postoperative day 1. In surgical management of exotropia, there is a widespread agreement that an initial overcorrection is needed for satisfacory correction because of a tendency towards postoperative exotropic drift.^16–18 Raab¹⁷ has reported that an overcorrection of 10–20 PD provides the best outcome, although good outcomes are also obtained with overcorrections in the range of 0–10 PD. Lee & Lee¹⁸ have reported that a postoperative day 1 overcorrection of 11–20 PD following BLR surgery and of 1–10 PD following R&R surgery can lead to good results. In the present study, mild esotropic distant deviation at postoperative day 1 was correlated with surgical success at postoperative 1 year.

Scott et al.¹⁹ have reported that the status of refraction and degree of anisometropic are prognostic factors. In the present study, the number of patients with anisometropia was higher in the recurrence group. Since amblyopia can affect the recurrence of IXT surgery,²⁰ patients with amblyopia were excluded to prevent the effect of amblyopia on recurrence after surgery. Although bilateral visual acuity is similar, the quality of the vision might be different resulting from anisometropia. Thus, it may interfere with fusion and binocularity in patients with IXT postoperatively and become a factor affecting poor surgical outcomes.

Gezer et al.¹² have reported that a preoperative exodeviation of 40 PD or more has a significantly greater likelihood of recurrence because of a positive correlation between preoperative and postoperative deviations. In the present study, preoperative deviation at near was significantly smaller and stereopsis based on titmus stereo test was better tendency in the success group. Better fusional ability and stereopsis could be factors affecting maintenance of IXT surgery.

Our study showed that surgical outcomes were favorable for patients who responded to preoperative part-time occlusion therapy, the most commonly used conservative treatment for IXT. Shin et al.²¹ have suggested that preoperative part-time occlusion therapy is a possible factor improving long-term surgical outcome. Our previous study has reported improvement in angle of deviation, control scores, and stereoacuity at distance and near after part-time occlusion therapy.²² Bang²³ has reported that a significantly higher surgical success rate in the improved control grade group. Suh²⁴ has reported that after 3 months of occlusion therapy for 3 h each day, near deviation measurements are decreased significantly in both basic and convergence-insufficiency types of intermittent exotropia, indicating that fusional ability is increased with part-time occlusion therapy. Therefore, we can hypothesize that patching can improve surgical results since it can improve fusional ability in intermittent exotropes.

This study has several limitations. First, since it was a retrospective study, inclusion criteria might be imprecise and the follow-up period was uneven. Second, although our study was the most comprehensive analysis, it might have potential selection bias and information bias. Patients showing satisfactory results were less likely to return to the clinic. Conversely, those showing unfavorable results were more likely to have been followed up longer. Findings from this population might have also been biased. Thirdly, when measuring the effect of patching, parameters used in this study, such as the magnitude of exodeviation, improvement of control score, and stereoacuity, might have variability depending on each child’s condition on the day of measurement which could lead to bias.

In conclusion, preoperative absence of anisometropia, good near stereoacuity, smaller exodeviation at near, and good response to occlusion therapy can be prognostic factors of favorable surgical results in patients with IXT. In addition, small esodeviation on postoperative day 1 was associated with better surgical outcomes. Therefore, preoperative patching and postoperative small esodeviation could lead to good surgical results.

We retrospectively reviewed medical records of 125 patients aged 3 to < 10 years who received surgical treatment between January 2019 and February 2021 at Pusan National University Yangsan Hospital with more than 12 months of postoperative follow-up. Patients with constant exotropia, a history of ocular surgery, A-V pattern strabismus, oblique muscle dysfunction, vertical strabismus, paralytic strabismus, restrictive strabismus, unilateral amblyopia, nystagmus, or a systemic disease such as cerebral palsy were excluded from this study.

The study protocol adhered to the Declaration of Helsinki tenets. The study protocol adhered to the Declaration of Helsinki tenets and was approved by the Institutional Review Board of Pusan National University Yangsan Hospital (IRB number: 05-2023-115). Since this was a retrospective study, the need for informed consent of subjects was waived by the IRB of Pusan National University Yangsan Hospital.

Clinical measurements

All patients underwent a complete ophthalmologic examination at the first visit. A visual acuity test for every patient was conducted with correction of refractive errors. Refractive errors were measured through cylcoplegic refraction. The magnitude of exodeviation was measured by alternate prism and cover test (APCT) at distance (6 m) and near (1/3 m) with accommodative target fixation.

Distant stereoacuity was assessed using a Distant Randot test at 3 meters (m). Near stereoacuity was assessed using the Randot Preschool Stereotest and Titmus Stereo fly test at 40 centimeters (cm). Worth-4-dot test was then done to measure the suppression or alternate fixation.

Strabismus surgery

The surgical procedure, which was performed by a single surgeon under general anesthesia, was primarily bilateral lateral rectus muscle recession (BLR). Surgical dosages were applied using Park’s method based on patient’s angle of deviation. Patients with convergence insufficiency type of exotropia underwent slanted BLR. The upper muscle fiber was recessed based on the distance angle of deviation and the lower muscle fiber was recessed based on the near angle of deviation.

Outcome measures

Surgical outcomes were grouped according to the angle of deviation at postoperative one year as follows: success (esophoria/tropia ≤ 5 prism diopers (PD) to exophoria/tropia ≤ 10 PD) and failure (esophoria/tropia > 5 PD or exophoria/tropia > 10 PD).

Patch responders (improved) were defined by one of the following criteria at 3-month visit: 1) decrease in the magnitude of exodeviation of 10Δ or more at distance and near from baseline, 2) improvement control score of 1 or more at distance or near, or 3) gain of stereoacuity of 2 octaves (0.6 log arcsec) or more at distance or near.

Factor associated with outcomes after surgery

We investigated various clinical factors possibly associated with surgical outcomes, including gender, visual acuity, refractive errors, the presence of anisometropia, age of diagnosis, age at surgery, type of exotropia, stereopsis, duration from diagnosis to surgery, magnitude of exodeviation preoperatively, and magnitude of exodeviation at postoperative day 1.

Anisometropia was defined as the difference of hyperopia > + 1.5 dioopters (D), myopia > -1.5D and /or astigmatism > + 1.5D. Patients were classified as having basic type IXT if the difference between distance and near exodeviation was within 10Δ. Divergence excess (DE) type was defined when the distance deviation was 10Δ greater than the near deviation. Pseudo-divergence excess (Pseudo-DE) type was defined when the patient exhibited greater exotropia at distance than near with the near deviation increased within 10Δ of the distance deviation after 60 minutes of monocular occlusion. Convergence insufficiency (CI) type was defined when the near deviation was 10Δ greater than the distance deviation.

Statistical Analysis

For categorical variables, Pearson’s chi-square test was used. Independent Student’s t-test was employed to compare continuous numerical variables. Before performing t-test, normality checks were conducted. Outcome group (success versus failure) comparisons were adjusted for baseline level of outcome using analysis of covariance. All p-values provided were obtained using a two-tailed test. SPSS version 20.0 (SPSS Inc, Chicago, IL, USA) was used for the analysis.

A logistic regression analysis was performed to identify factors associated with surgical outcomes. Each variable was analyzed using a univariate model. Significant variables were subsequently evaluated using a multivariate model. Odds ratio (OR) and confidence interval (CI) of logistic regression are reported. P-value < 0.05 was considered to be statistically significant.

Data availability

The datasets generated during or analysed during the current study are available from the corresponding author on reasonable request.

Additional information

a. Funding / Support: This study was supported by a 2023 research grant from Pusan National University Yangsan Hospital.

b. Financial Disclosures: There are no financial disclosures.

c. Other Acknowledgements: None.

d. Competing interests : The author(s) declare no competing interests.

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No competing interests reported.

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Factors Associated with Surgical Outcomes of Intermittent Exotropia in Children

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Version 1

Abstract

Purpose

Methods

Results

Conclusions

Introduction

Results

Discussion

Patients and Methods

Clinical measurements

Strabismus surgery

Outcome measures

Factor associated with outcomes after surgery

Statistical Analysis

Declarations

References

Additional Declarations

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