Journal of Pediatric Ophthalmology and Strabismus

Original Article 

Recovery From Suppression With Successful Motor Alignment After Surgery for Intermittent Exotropia

Jungah Huh, MD; Suk-Gyu Ha, MD, PhD; Seung-Hyun Kim, MD, PhD

Abstract

Purpose:

To investigate recovery from suppression when the target motor alignment is achieved following surgery for intermittent exotropia.

Methods:

The medical records of 237 patients who underwent surgery for exotropia were retrospectively reviewed. The age at surgery, sex, preoperative angle of deviation, suppression status, and near stereopsis were investigated. Suppression status was classified as no, alternate, or constant suppression. Target motor alignment was defined as 10 prism diopters (PD) or less of exodeviation or 2 PD of esodeviation at the final visit.

Results:

The mean age at surgery was 8.2 ± 3.2 years and 115 (48.5%) patients were male. The preoperative angle of deviation was 26.3 ± 5.9 PD and the follow-up postoperative period was 21.6 ± 7.6 months. The preoperative suppression status included 23 (9.7%), 55 (23.2%), and 159 (67.1%) patients who showed no, alternate, or constant suppression, respectively. Two hundred fifteen (90.7%) patients obtained the target motor alignment by the final visit. Of the 144 patients who demonstrated constant suppression preoperatively but achieved the target motor alignment postoperatively, 12 (8.3%) patients demonstrated residual suppression. All 12 of these patients had a preoperative angle of exotropia of greater than 20 PD.

Conclusions:

Most patients undergoing surgery for intermittent exotropia obtained both successful motor alignment and fusion postoperatively. However, successful motor alignment did not guarantee recovery of suppression when the preoperative angle of exotropia was greater than 20 PD. The preoperative factors and functional implications underlying this finding are unclear and merit further study.

[J Pediatr Ophthalmol Strabismus. 2020;57(1):21–26.]

Abstract

Purpose:

To investigate recovery from suppression when the target motor alignment is achieved following surgery for intermittent exotropia.

Methods:

The medical records of 237 patients who underwent surgery for exotropia were retrospectively reviewed. The age at surgery, sex, preoperative angle of deviation, suppression status, and near stereopsis were investigated. Suppression status was classified as no, alternate, or constant suppression. Target motor alignment was defined as 10 prism diopters (PD) or less of exodeviation or 2 PD of esodeviation at the final visit.

Results:

The mean age at surgery was 8.2 ± 3.2 years and 115 (48.5%) patients were male. The preoperative angle of deviation was 26.3 ± 5.9 PD and the follow-up postoperative period was 21.6 ± 7.6 months. The preoperative suppression status included 23 (9.7%), 55 (23.2%), and 159 (67.1%) patients who showed no, alternate, or constant suppression, respectively. Two hundred fifteen (90.7%) patients obtained the target motor alignment by the final visit. Of the 144 patients who demonstrated constant suppression preoperatively but achieved the target motor alignment postoperatively, 12 (8.3%) patients demonstrated residual suppression. All 12 of these patients had a preoperative angle of exotropia of greater than 20 PD.

Conclusions:

Most patients undergoing surgery for intermittent exotropia obtained both successful motor alignment and fusion postoperatively. However, successful motor alignment did not guarantee recovery of suppression when the preoperative angle of exotropia was greater than 20 PD. The preoperative factors and functional implications underlying this finding are unclear and merit further study.

[J Pediatr Ophthalmol Strabismus. 2020;57(1):21–26.]

Introduction

The surgical goal for patients with intermittent exotropia is to achieve successful motor alignment and improved sensory function. Surgical treatment should be considered to prevent deterioration of control, stereoacuity, suppression, and increasing the amount of exodeviation.1 In eyes with intermittent exotropia, images fall into the fovea of the fixating eye and a noncorresponding retinal point in the deviating eye, resulting in sensory adaptations such as suppression and abnormal retinal correspondence.2 Central suppression occurs most often in children.3 Thus, recovery of binocular fusion is an important goal in the treatment of intermittent exotropia.

Previous studies have suggested that suppression can occur in patients with intermittent exotropia during increasing deviation or during the tropic phase.4,5 Thus, identification of suppression would be a reliable predictor of sensory fusional status in patients with intermittent exotropia. In general, the angle of deviation has been connected to the ability to control exotropia. However, there is little knowledge of the relationship between stable angle of deviation and status of suppression after surgery in patients with intermittent exotropia.

Clinical factors that influence the outcome of surgery, although disputable, include the preoperative and postoperative angle of deviation, stereoacuity, amblyopia, oblique muscle dysfunction, surgical methods, and type of exotropia.6–9

To the best of our knowledge, there has been no report of recovery from central suppression after surgery that included a large number of patients with intermittent exotropia. The aim of this study was to investigate the clinical factors associated with the recovery from suppression with successful postoperative target motor alignment in patients with intermittent exotropia.

Patients and Methods

This study protocol was approved by the Korea University Medical Center institutional review board and adhered to the tenets of the Declaration of Helsinki. This retrospective study included patients who underwent strabismus surgery between January 2014 and December 2016 for intermittent exotropia. Intermittent exotropia was defined as a near deviation measuring within 10 prism diopters (PD) of the distance deviation. Patients with convergence insufficiency or divergence excessive type of exotropia, recurrent exotropia, paralytic strabismus, amblyopia, previous history of surgery for strabismus, or neurologic deficits were excluded.

Preoperative data included the patient's age, sex, preoperative angle of deviation (PD) at distance and near, near stereoacuity (Stereo Fly SO-001 test; Stereo Optical Co., Chicago, IL), and the presence of suppression (Vectographic projector test [L39]; Luneau Technology, Luneau, France) at distance. The Vectographic projector test consists of two superimposed polarized slides of letters that project on an aluminized screen that reflects the images while preserving polarization. The patient is asked to read the letters (or picture) on the screen while wearing polarized glasses. The polarization of glasses and the projected slides are oriented so that some of the letters (or picture) are only seen with the right eye, whereas some are only seen with the left eye and others are seen with both eyes. Patients with normal bifoveal fusion will see all of the letters. If suppression is present, the letters projected only to the suppressed eye will not be seen. The angle of deviation was measured by an alternate prism cover test at distance and at near.

Surgery was performed by a single experienced surgeon (S-HK). A unilateral or bilateral lateral rectus muscle recession was performed according to the preoperative angle of deviation. The surgical dose was determined by the preoperative angle of deviation, as recommended by a surgical table.10 All patients were treated with an alternate part-time occlusion (2 to 8 hours per day) therapy protocol postoperatively to avoid diplopia. The duration of occlusion was prescribed according to the postoperative angle of deviation and presence of diplopia. Occlusion was discontinued in patients who obtained orthotropia. Postoperative assessments were conducted at 1 day and 1, 3, 6, and 12 months after surgery, with annual follow-up visits thereafter. The angle of deviation at distance and near, near stereoacuity, and central suppression at distance were measured at each visit. Only patients who were observed for at least 12 months after surgery were included in the study. The preoperative and postoperative suppression statuses were classified as no, alternate, or constant suppression. Target motor alignment was defined as 10 PD or less of exodeviation or 2 PD of esodeviation at the final visit. We analyzed the suppression status of patients with target motor alignment at the final visit. For patients who demonstrated constant suppression preoperatively, postoperative improvement in suppression was defined as no suppression or alternate suppression at the final visit. Patients who continued to demonstrate constant suppression at the final visit were classified as demonstrating residual suppression.

All statistical analyses were performed using IBM SPSS Statistics for Windows (version 21.0; IBM Corporation., Armonk, NY). The chi-square test and Mann–Whitney U test were used to compare the measurements between subgroups. A multiple linear regression analysis was performed to identify factors that statistically contributed to the recovery of suppression after surgery. A P value of .05 or less was considered statistically significant.

Results

A total of 237 patients with intermittent exotropia were included in this study. The mean age at surgery was 8.2 ± 3.2 years (range: 4 to 27 years). There were 115 (48.5%) male patients. Preoperative angle of deviation was 26.3 ± 5.9 PD (range: 14 to 45 PD) and 26.9 ± 6.2 PD (range: 10 to 45 PD) at distance and near, respectively. The median preoperative near stereoacuity was 100 arc seconds (range: 60 to 800 arc seconds). The unilateral and bilateral lateral rectus muscle recessions were performed in 26 (11.0%) and 211 (89.0%) patients, respectively. The mean follow-up period was 21.6 ± 7.6 months (range: 12 to 36 months). The postoperative angle of deviation measured 1.7 ± 4.3 PD (range: −18 to 20 PD) and 1.3 ± 4.4 PD (range: −18 to 20 PD) at distance and near, respectively. A negative value indicated esodeviation. Thirty-four patients (14.3%) had inferior oblique overaction. Twenty-three (9.7%) patients had no suppression, 55 (23.2%) patients had alternate suppression, and 159 (67.1%) patients had constant suppression.

Two hundred fifteen (90.7%) patients achieved the target motor alignment at the final visit. The patients were divided into two subgroups (20 PD or less and greater than 20 PD) according to the pre-operative angle of deviation. Of the 60 patients with a preoperative angle of deviation of 20 PD or less, 31 demonstrated preoperative constant suppression; all (100%) showed no residual suppression at the final visit. Of the 15 patients with preoperative alternate suppression, only 2 (13.3%) demonstrated alternate suppression at the final visit (Table 1). Of 155 patients with a preoperative angle of deviation of greater than 20 PD, 113 patients had pre-operative constant suppression. Of these, only 12 (10.6%) patients showed constant suppression at the final visit. Of the 35 patients with preoperative alternate suppression, 1 patient (2.9%) deteriorated in sensory status to constant suppression at the final visit (Table 1).

Changes in Suppression Status of Patients With Target Motor Alignment at the Final Visit According to the Preoperative Angle of Deviation

Table 1:

Changes in Suppression Status of Patients With Target Motor Alignment at the Final Visit According to the Preoperative Angle of Deviation

In patients with target motor alignment at the final visit, 179 (77.8%) had improvement of suppression, with only 13 (5.5%) patients demonstrating residual suppression at the final visit, respectively. Table 2 includes a comparison of the clinical features of patients who experienced an improvement in suppression and residual suppression at the final visit. There were no significant differences in sex, age at surgery, presence of combined inferior oblique overaction, median near stereoacuity, or follow-up periods between the two groups (all P > .05) (Table 2).

Comparisons of Clinical Features Between Patients With Improved Suppression and Residual Suppression at the Final Visit

Table 2:

Comparisons of Clinical Features Between Patients With Improved Suppression and Residual Suppression at the Final Visit

However, the preoperative angle of deviation in patients with residual suppression (32.1 ± 5.0 PD; range: 25 to 45 PD) was significantly greater than that of patients with an improved suppression (26.3 ± 5.7 PD; range: 14 to 45 PD) at the final visit (P = .01) (Table 2).

In a multiple linear regression test, there was a significant correlation between residual suppression after surgery preoperative angle of deviation of greater than 20 PD (P = .04). However, there were no significant correlations between residual suppression after surgery and male gender, age at surgery, presence of inferior oblique overaction, and preoperative median near stereopsis (Table 3).

Multiple Linear Regression Analysis of Clinical Characteristics With Residual Suppression at Final Visit

Table 3:

Multiple Linear Regression Analysis of Clinical Characteristics With Residual Suppression at Final Visit

Discussion

If different images are presented to the foveas of each eye, the images are not perceived simultaneously in patients with strabismus. Suppression is an adaptive mechanism to overcome the visual confusion or diplopia resulting from strabismus. Thus, distance suppression could occur in patients with intermittent exotropia and identification of distance suppression could be important to evaluate binocular field of vision. O'Neal et al.11 proposed that central suppression is a precursor to significant loss of distance stereoacuity.

The identification of suppression in patients with intermittent exotropia may help predict the natural course or prognosis of sensory fusional status after surgery. In this study, the Vectographic projector test was used to evaluate distance suppression. Abroms et al.12 demonstrated that a Vectographic projector test might be more sensitive than distance stereoacuity for identification of the loss of binocular function.

Theoretically, bifoveal fixation of the same target image could be not suppressed in normal retinal correspondence within orthotropic motor alignment. This study included patients with postoperative residual suppression, although they had target motor alignment and 10 PD or less of exodeviation at the final visit. Many studies defined the postoperative success of patients with intermittent exotropia as target motor alignment, orthotropia, or 10 PD or less of exodeviation. The success rate in this study was 90.7% at the final visit. The surgical success rate of bilateral lateral rectus muscle recession has been reported to range from 68% to 89%. The surgical results in this study were successful compared to previous studies.13–16

In the current study, residual suppression after surgery was observed in 10.6% of patients with constant suppression and preoperative intermittent exotropia greater than 20 PD. Yildirim et al.17 demonstrated that patients with central fusion were unlikely to improve their distance stereoacuity postoperatively. They stated that successful surgery may improve distance stereoacuity. However, we speculated that the postoperative residual suppression may have a relationship with the larger preoperative angle of deviation in exotropia.

Richard and Parks18 demonstrated that target motor alignment is not affected by age at surgery, strabismus duration, or age of onset of exotropia. Generally, surgery is considered to achieve target motor alignment in patients with intermittent exotropia. However, 10.6% of patients had residual suppression with target motor alignment after surgery. We speculate that the recovery of bifoveal fusion in patients with intermittent exotropia could be another concern in the treatment of intermittent exotropia.

Previous studies have demonstrated that a larger preoperative angle of deviation is the most important determining factor of a successful outcome in patients with exotropia.19,20 Therefore, patients with larger preoperative deviations have a decreased chance of a successful surgical outcome.21 We speculate that a preoperative angle of deviation of 20 PD or greater of exodeviation could have affected the binocular sensory outcomes in this study.

In a previous study, clinical factors affecting the response to surgery for exotropia included the patient's age, degree of control, sensory function, and tenacious fusion at near.1 Postoperative superior sensory function in exotropia was associated with early surgery and a shorter duration of strabismus.12 However, Richard and Parks demonstrated that target motor alignment is not affected by age at surgery, strabismus duration, or age of onset of exotropia.18

Previous studies reported that sensory fusional function could be affected by the angle of deviation or constancy or duration of exotropia. Ball et al.22 reported that a long-standing large angle of constant exotropia achieved stereoacuity following strabismus surgery. They speculated that excellent motor alignment is achieved in constant exotropia with bifoveal fixation. Previous studies reported that the postoperative bifoveal fixation rate is low for infantile and constant exotropia.23,24 Although the factors contributing to better sensory outcomes following surgery are unknown, we speculate that there is a possibility of residual suppression at distance while maintaining good motor alignment in patients with intermittent exotropia. To the best of our knowledge, this study is the first report of the recovery of suppression that included a large number of patients with intermittent exotropia and a long postoperative follow-up period.

This study had some limitations. First, it was a retrospective medical chart review. Second, we did not monitor other clinical factors, such as the control level, surgical method, duration of intermittent exotropia, or distance stereoacuity in this study. Several clinical factors may affect the surgical results. There was variability in categorizing and quantifying a patient's control level in patients with intermittent exotropia.25 The control level and duration of intermittent exotropia might affect the prognosis and surgical outcome.26 Third, all patients in this study had intermittent exotropia. Other types of exotropia may affect the surgical results. Fourth, we evaluated suppression status by Vectographic projector. The suppression test, including the Worth 4-dot test, was not performed in this study. Fifth, we reviewed the medical records of patients who underwent a bilateral or unilateral lateral rectus muscle recession. Postoperative motor and sensory outcome could be affected by different surgical methods.

Residual suppression can be observed even when target motor alignment is achieved following surgery for intermittent exotropia. Patients with good postoperative motor alignment may require careful consideration to recover postoperative distance suppression.

References

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Changes in Suppression Status of Patients With Target Motor Alignment at the Final Visit According to the Preoperative Angle of Deviation

Preoperative Angle of Deviation of ≤ 20 PD (n = 60)

Final Suppression StatusNo Suppression (n = 14)Alternate Suppression (n = 15)Constant Suppression (n = 31)
No suppression (%)14 (100)13 (86.7)
Alternate suppression (%)2 (13.3)
Constant suppression (%)31 (100)
Preoperative Angle of Deviation of > 20 PD (n = 155)

Final Suppression StatusNo Suppression (n = 7)Alternate Suppression (n = 35)Constant Suppression (n = 113)
No suppression (%)7 (100)30 (85.7)99 (87.6)
Alternate suppression (%)4 (11.4)2 (1.8)
Constant suppression (%)1 (2.9)12 (10.6)

Comparisons of Clinical Features Between Patients With Improved Suppression and Residual Suppression at the Final Visit

CharacteristicImproved Suppression (n = 175)Residual Suppression (n = 13)P
Male (%)86 (49.1)7 (58.3).53a
Age at surgery (years)8.1 ± 2.9 (4 to 24)8.8 ± 6.2 (5 to 27).76b
IOOA (%)27 (15.4)2 (16.7).27a
Preoperative angle of deviation (PD)26.3 ± 5.7 (14 to 45)32.1 ± 5.0 (25 to 45).01b
Angle of deviation at final visit (PD)1.3 ± 2.3 (0 to 10)3.2 ± 3.4 (0 to 10).04b
Median near stereopsis at final visit (arc seconds)100 (60 to 800)100 (60 to 400).42a
Follow-up period (months)21.7 ± 7.5 (12 to 36)24.5 ± 8.3 (12 to 36).71b

Multiple Linear Regression Analysis of Clinical Characteristics With Residual Suppression at Final Visit

CharacteristicBtP
Male0.011.06.29
Age at surgery0.12−1.24.22
IOOA0.190.62.53
Preoperative angle of deviation of > 20 PD0.381.72.04
Preoperative median near stereopsis0.513.51.55
Authors

From the Department of Ophthalmology, Korea University College of Medicine, Seoul, South Korea.

The authors have no financial or proprietary interest in the materials presented herein.

The authors thank Kyung-Sook Yang, PhD, a biostatistician at the Korea University College of Medicine, Department of Biostatistics, for her help with statistical analysis of this study.

Correspondence: Suk-Gyu Ha, MD, PhD, Korea University Guro Hospital, 148 Gurodong-ro, Guro-dong, Guro-gu, Seoul 08308, South Korea. E-mail: sukgyu.ha@gmail.com

Received: April 09, 2019
Accepted: September 12, 2019

10.3928/01913913-20191016-03

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