Lateral incomitancy and surgical results in intermittent exotropia

Divergence excess and basic exotropia types of intermittent exotropia: a major review. Part 1: prevalence, classification, risk factors, natural history and clinical characteristics

INTRODUCTION

Intermittent exotropia (IXT) is a common form of strabismus. It is an outward deviation of one eye typically when viewing at distance. Symptoms include, but are not limited to double vision, eyes feeling tired, excessive blinking, and reduced quality of life. Its clinical characteristics are distinctive from other types of strabismus. This paper provides a comprehensive review of prevalence, classification, risk factors, natural history and clinical characteristics of the divergence excess and basic exotropia types of IXT.

METHODS

Search strategies involving combination of keywords including intermittent exotropia, exotropia, divergences excess, basic exotropia, prevalence, incidence, classification, terminology, risk factor, natural history, observation, angle of deviation, control, control score, symptom, quality of life, suppression, anomalous retinal correspondence, AC/A, accommodative convergence/accommodation, accommodative convergence, convergence, accommodation, vergence, incomitance and vertical were used in Medline. All English articles from 1900/01/01 to 2020/09/01 were reviewed. The reference list of the identified article was also checked for additional relevant article. Studies focused on animal model or strabismus associated with neurologic disorder or injury were excluded.

RESULTS

The estimated prevalence of IXT in children ranges from 0.1% to 3.7%. Hypoxia at birth and being female are potential risk factors of IXT. Using validated measures of control, multicenter prospective studies showed that the rate of conversion from IXT to constant exotropia is low. The angle of deviation is the most reported outcome measure in studies of IXT. It is often used to represent the severity of the condition and has been suggested as one of the four core outcomes for studies of the surgical management of IXT. Control of exodeviation is one of the four suggested core outcomes for study of surgery of IXT and is considered the main parameter of disease severity. Several validated tools for quality of life score are available to evaluate the subjective severity of IXT.

DISCUSSION

We reviewed the prevalence, classification, risk factors, natural history and clinical characteristics of the divergence excess and basic exotropia types of IXT. Further research into these areas, especially its clinical characteristics (e.g. suppression, dual retinal correspondence), will increase our understanding of this condition and potentially lead to better management of this common form of strabismus.

Long-term surgical outcomes of basic-type exotropia in patients with hyperopia

BACKGROUND

To investigate the surgical outcomes of basic-type exotropia in patients with hyperopia.

METHODS

The medical records of patients who underwent surgery for basic-type exotropia and had been followed up for ≥ 2 years were retrospectively recruited. Patients with myopia and spherical equivalent (SE) < -1.0 diopters (D) were excluded. The patients were classified according to the SE: group H had a SE ≥  + 1.0 D, and group E had -1.0 ≤ SE <  + 1.0 D. The surgical success rate and sensory outcome were compared. Surgical success was defined as exodeviation ≤ 10 prism diopters (PD) and esodeviation ≤ 5 PD at 6 m fixation. Stereoacuity was measured using the Titmus Preschool Stereoacuity Test.

RESULTS

Seventy-five patients (24 males and 51 females, mean age 5.1 ± 2.6 years, range 2.7-14.8) were included. The SE ranged from -0.9 to 4.4 and 21 patients were classified into group H and 54 into group E. The success rates were higher in group H than in group E during the entire follow-up period, but the differences were significant only at the final examination. At the final follow-up, 11 of the 21 (52.4%) patients in group H and 15 of the 54 (27.7%) in group E maintained successful alignment, whereas 10 (47.6%) and 38 (70.4%) patients exhibited recurrence. Overcorrection was exhibited in one (1.9%) patient in group E. Sensory results were comparable between the groups. The follow-up period did not differ between the two groups. The survival analysis showed no difference in the surgical results between the two groups.

CONCLUSIONS

Surgery for basic-type intermittent exotropia resulted in superior outcomes in patients with hyperopia compared to those with emmetropia.

Results of Unilateral Lateral Rectus Recession Surgery in 15 - 30 PD Intermittent Exotropia

PURPOSE

To evaluate the surgical outcomes of unilateral lateral rectus muscle recession (ULR) with low surgical dosage in patients with intermittent exotropia (IXT) of 15 - 30 prism dioptres (PD).

METHODS

We retrospectively analysed 92 eyes of 92 patients who underwent ULR surgery with the diagnosis of IXT of 15 - 30 PD at distance fixation between January 2017 and June 2019. ULR surgery of 6.5 mm was performed for exotropia of 15 - 20 PD, 7.5 mm for that of 20 - 25 PD, and 8.5 mm for that of 25 - 30 PD and postoperative results were evaluated at the 1st week, 1st month, 6th month, and the 2nd year. Orthophoria or IXT less than 10 PD was accepted as successful.

RESULTS

The mean preoperative deviation angle at distance was 22.3 ± 4.4 PD. Mean postoperative deviation angles at distance were 2.5 ± 1.7, 3.9 ± 2.4, 6.5 ± 3.0, and 8.7 ± 3.1 at 1 week, 1 month, 6 months, and 2 years, respectively. The surgical success rate of ULR was 100, 96.7, 84.7, and 77.1% at the 1st week, 1st month, 6th month, and the 2nd year, respectively. In the long-term results, there were no complications such as lateral gaze incomitance, overcorrection, or deterioration in stereopsis.

CONCLUSION

Using the ULR technique, we were able to obtain effective surgical results in IXT with less surgical dosage and without any serious complications. ULR surgery can be used as an effective method in patients with IXT of 15 - 30 PD.

Comparative Study of Bilateral Versus Unilateral Strabismus Surgery in the Management of Lateral Incomitance in Intermittent Exotropia

PURPOSE

To evaluate and compare bilateral asymmetric lateral rectus recession versus unilateral resection-recession surgery in the management of lateral incomitance in intermittent exotropia.

METHODS

A prospective randomized interventional comparative study was conducted consisting of 80 patients with intermittent exotropia (older than 7 years) having significant lateral incomitance. They were equally divided into two groups by a sealed envelope system. The bilateral group underwent bilateral asymmetric lateral rectus recession and the unilateral group underwent unilateral lateral rectus recession and medial rectus resection based on post-patch deviation. Parameters assessed were change in horizontal deviation, change in lateral incomitance, binocularity, motility limitation, and complications, if any. Surgical outcome was considered successful if the primary deviation was within ±8 prism diopters (PD) and lateral incomitance was less than 5 PD.

RESULTS

The mean lateral incomitance preoperatively and postoperatively was 8.3 ± 1.6 and 2.8 ± 2.4 PD in the bilateral group and 8.9 ± 1.4 and 3.7 ± 2.5 PD in the unilateral group, respectively. There was no statistically significant difference in the postoperative lateral incomitance between the two groups (P = .25), but a statistically significant difference was observed between preoperative and postoperative lateral incomitance in each group (P < .0001).

CONCLUSIONS

Both procedures are equally efficacious in achieving acceptable ocular alignment and improving significant lateral incomitance in patients with intermittent exotropia with deviations between 15 and 35 PD without causing significant motility limitation. [J Pediatr Ophthalmol Strabismus. 20XX;X(X):XX-XX.].

Evaluation of Efficacy and Lateral Gaze Incomitance in Symmetrical and Asymmetrical Surgery for Concomitant Esotropia and Exotropia

Purpose

Evaluation of asymmetrical and symmetrical horizontal strabismus surgery as regards efficacy and postoperative lateral gaze incomitance.

Patients and Methods

This prospective comparative interventional case series study included 40 patients of age more than 3 years with alternating horizontal strabismus. Patients were divided according to the type of horizontal deviation into esotropia and exotropia groups, which were further subdivided into asymmetrical and symmetrical subgroups in each type. The surgery was defined as symmetrical procedure if the surgery was done on the same muscle in the two eyes and it was defined as asymmetric in recess-resect procedures in one eye, and three horizontal muscles surgery. Preoperative and postoperative measurements were done in primary position, right, and left gaze using alternate prism cover test and hand-held orthopedic goniometer.

Results

At the end of follow-up period, a statistically insignificant difference (P value = 0.8057) was present in the success rate between the asymmetrical and symmetrical subgroups of esotropia (90 and 86.67%, respectively) and it was 100% in both exotropia subgroups. Lateral gaze incomitance results were different between esotropia and exotropia subgroups. In esotropia, a statistically significant difference was reported at 1 month (0.009), which became insignificant at 6 months (0.077) and 12 months (0.077) between asymmetrical and symmetrical subgroups. In exotropia subgroups, there was a statistically insignificant difference in lateral gaze incomitance at 1, 6, and 12 months (P = 1).

Conclusion

Asymmetrical procedure had the same efficacy and success rate of symmetrical procedure for the correction of concomitant horizontal deviations in primary gaze without persistent postoperative lateral gaze incomitance, especially in exotropia.

Clinical Trial Registration

NCT04199286.

Quantitative Analysis of Eyeball Rotation During Lateral Gaze in Intermittent Exotropia: A Magnetic Resonance Imaging Study

Purpose

To evaluate the eyeball rotation during lateral gaze in patients with intermittent exotropia (IXT) using three-dimensional magnetic resonance imaging (MRI).

Methods

In this prospective observational study, patients with IXT (n = 29) underwent orbital MRI during central, right, and left gazes. Fixation targets were placed at a 40° angle for lateral gaze. After acquisition of MR images, the position of the static tissues other than the eyeball in the MR images were matched three-dimensionally. The optical axis was defined as the perpendicular line to its lens passing through the corneal vertex. The rotation angle was measured as the angle between optical axes in central gaze and lateral gaze using ImageJ. A difference of 3° or more in the rotational angle between both eyes was considered a significant difference.

Results

Eight patients (26.7%) had a larger adduction angle than the abduction angle of the fellow eye and six patients (20.0%) showed a smaller adduction angle during lateral gaze on at least one side. There was no significant factor associated with the pattern of rotation.

Conclusions

Almost one-half of the patients with IXT had significant difference in the rotation angle between both eyes during lateral gaze. Measurement of the rotation angle during lateral gaze using MRI showed that IXT is not a perfectly comitant disturbance of gaze in some subjects.

Translational Relevance

Quantitative analysis for eye movements using MRI can provide useful information for physiologic mechanism and proper surgical planning in patients with IXT.

Consecutive Esotropia with and without Abduction Limitation - Risk Factors and Surgical Outcomes of Lateral Rectus Advancement

Purpose: To identify risk factors for abduction limitation in consecutive esotropia following surgical correction of exotropia. To study outcomes of lateral rectus advancement for consecutive esotropia correction.Methods: Patients with consecutive esotropia (>10PD) operated between 2007 and 2019 with a minimum follow-up of 2 months were reviewed retrospectively. Preoperative and postoperative alignment and ocular motility were recorded. Patients were classified into those with full abduction (group-A) and with abduction limitation (group-B). Success was defined as deviation ≤10 PD of esotropia or exotropia in the primary position.Results: Forty-cases fulfilled the inclusion criteria (group-A = 28 and group-B = 12). Median age at surgery was five years, median consecutive esotropia was 20PD and follow-up was 29.18 months. Abduction limitation (group-B) was associated with constant exotropia (p = .01) and larger bilateral lateral rectus recession (group-A = 13 mm, group-B = 15 mm; p = .04). Nineteen patients underwent lateral rectus advancement (group-A = 12, group-B = 7), one underwent medial-rectus recession and two were excluded due to lack of postoperative follow-up. Five patients had spontaneous resolution with good alignment (group-A = 3, group-B = 2), two refused surgery, three were observed and eight were lost to follow-up. Success following second surgery was similar in both groups (group-A = 86%, group-B = 77%)(p = 1).Conclusion: Constant exotropia and larger lateral rectus recession were associated with abduction limitation in consecutive esotropia. Lateral rectus advancement produced good outcomes irrespective of abduction limitation.

Surgical management of intermittent exotropia: do we have an answer for all?

Intermittent exotropia (X(T)) is one of the most common form of strabismus with surgery being the mainstay of treatment. The main goal of surgery is to preserve binocular vision and stereopsis and to prevent its further loss. The decision to operate is mainly based on four aspects: increasing angle of exodeviation, deteriorating control of X(T), decrease in stereopsis for near or distance and quality of life. Bilateral lateral rectus muscle recession and unilateral lateral rectus recession with medial rectus resection, are the two most common surgical procedures performed and have been studied extensively in basic, divergence excess and convergence insufficiency types of X(T). However, there is no consensus over the relative efficacy of the two procedures in terms of postoperative alignment, residual or recurrent exotropia and consecutive esotropia with widely variable results, which can be attributed to poor understanding of the natural course of the disease. Multiple demographic, clinical and anatomic features that may influence the surgical outcomes have been studied to explain this variability. Moreover, most of the evidence regarding surgical outcomes of X(T) is from retrospective studies and the ongoing randomised prospective trials can shed light on long-term efficacy of these procedures. The goal of this review is to give a comprehensive overview of the outcomes of various surgical techniques in the management of different types of X(T), the preoperative and postoperative factors that may affect the surgical outcomes and to discuss the dilemmas faced by the treating surgeons including the effective management of overcorrection and undercorrection.

A comparison of surgical outcomes between pre-and full-term patients with exotropia

PURPOSE

To compare the surgical outcomes between pre- and full-term patients with exotropia and to examine the factors associated with surgical outcomes.

METHODS

This retrospective study included 48 pre- and 432 full-term patients with basic-type exotropia who underwent unilateral or bilateral lateral rectus muscle (ULR or BLR) recession. Preoperative characteristics and surgical outcomes were compared between the pre- and full-term infants. Additionally, factors affecting the surgical outcomes were evaluated in all patients.

RESULTS

The preoperative characteristics were significantly different between the pre- and full-term groups in terms of neurodevelopmental disabilities (p = 0.020). There were no significant differences between the pre- and full-term groups in terms of the success, overcorrection, and recurrence rates after the mean follow-up period of 34.6 ± 13.9 months (p = 0.697). The major cause of surgical failure was recurrence in both groups. Pre-term birth was not a risk factor for overcorrection and recurrence. However, regardless of the pre- or full-term birth status, the presence of neurodevelopmental disabilities significantly affected final overcorrection (p = 0.004).

CONCLUSIONS

Pre-term patients with exotropia showed similar surgical outcomes to full-term controls. The presence of neurodevelopmental disabilities was a risk factor for final overcorrection.

Incomitance and Eye Dominance in Intermittent Exotropia

Purpose

To determine if the deviation angle changes in subjects with intermittent exotropia as they alternate fixation between the right and left eye in primary gaze.

Methods

In this prospective observational cohort study, 37 subjects with intermittent exotropia were tested for evidence of incomitance. The position of each eye was recorded with a video tracker during fixation on a small central target. A cover-uncover test was performed by occluding one eye with a shutter that passed infrared light, allowing continuous tracking of both eyes. The deviation angle was measured during periods of right eye and left eye fixation. Incomitance was assessed as a function of eye preference, fixation stability, and exotropia variability.

Results

The mean exotropia was 18.2° ± 8.1°. A difference between right exotropia and left exotropia was detectable in 16/37 subjects. Allowing for potential tracking error, the incomitance had a mean amplitude of 1.7°. It was not related to a difference in accommodative effort, eye preference, fixation stability, or variability in deviation.

Conclusions

Comitance is regarded as a feature that distinguishes strabismus from paralytic or restrictive processes. Unexpectedly, eye tracking during the cover-uncover test showed that incomitance is present in approximately 40% of subjects with intermittent exotropia. It averages 10% of the exotropia, and can equal up to 5°. When substantial, it may be worth considering when planning surgical correction.