Clinical exhibition of increased accommodative loads for binocular fusion in patients with basic intermittent exotropia

Exploring the Link: A Systematic Review and Meta-Analysis on the Prevalence and Association Between Refractive Errors and Intermittent Exotropia

Background and Aims

Refractive errors and intermittent exotropia are prevalent conditions in pediatric populations, impacting visual development and quality of life. Despite the co-occurrence of conditions such as myopia, hypermetropia, and astigmatism with strabismus, comprehensive analyses of their coexistence are limited. This study aims to investigate the prevalence and characteristics of refractive error among children with intermittent exotropia and find the correlation between the angle of deviation for far and near with factors like mean spherical equivalent and age.

Methods

A systematic review and meta-analysis were conducted in accordance with PRISMA guidelines. PubMed and Scopus databases were searched up to February 13, 2024. Inclusion criteria encompassed studies detailing clinical presentation, management strategies, and outcomes, while exclusion criteria eliminated review articles, conference abstracts, animal research, and studies with inadequate clinical information. Data extraction and quality assessment were independently performed by multiple reviewers, with discrepancies resolved through consensus. Forest plot was used to show the mean spherical equivalent and the angle of deviation, while publication bias was demonstrated using funnel plot with Egger test.

Results

The search yielded 932 articles, with 23 meeting the inclusion criteria. Studies represented four geographical regions, with a combined sample size of 5407 participants aged 3-10 years. The mean refractive errors varied widely, with an overall pooled mean of -1.787 (95% CI: -5.392 to 1.818). Overminus lens therapy and surgical interventions were common management strategies, with surgery prevalent in cases with higher distant angle deviation. The myopia was more prevalent than hypermetropia (26.82%/16.10%). Meta-regression showed that the mean spherical equivalent had a significant effect on the angle of deviation far and near.

Conclusion

There was a significant correlation between myopia and intermittent exotropia in Middle Eastern and Asian pediatric populations. Myopia is notably more prevalent with significant effect of mean spherical equivalent on near-angle deviation.

Refractive change in pediatric patients with intermittent exotropia

PURPOSE

To determine the relationship between intermittent exotropia (IXT) and refractive change and the effects of the methods applied in IXT follow-up on refractive change.

METHOD

The medical records of 228 patients with IXT (group 1) and 110 patients without strabismus (group 2) who were followed between 2008 and 2022 were analyzed retrospectively. Group 1 was divided into three subgroups: overminus correction (group 1A), patients who underwent surgery (group 1B), and patients who were observed (group 1C).

RESULTS

Annual myopic progression was -0.21 ± 0.32 D (range, -1.26 to +1.92) in group 1 and -0.07 ± 0.30 D (range, -1.13 to +1.00) in group 2 (P < 0.001). Annual myopic progression was -0.26 ± 0.29 D (range, -1.26 D to +0.12 D) in group 1A, -0.25 ± 0.35 D (range, -1.15 D to +0.25 D) in group 1B, and -0.19 ± 0.33 D (range, -1.12 D to +1.92 D) in group 1C. There was no difference in annual myopic progression between the subgroups (P = 0.670). The annual change in myopic refraction between each of the group 1 subgroups and group 2 was statistically significantly different (P < 0.001, P = 0.023, P < 0.001, resp.).

CONCLUSIONS

Myopia progression was significantly greater in children with IXT than in the normal population. Myopia progression did not vary with exotropia treatment.

Refractive error changes and associated asthenopia observed after COVID-19 infection: Case reports from two continents

COVID-19 infection has been linked to various ocular complications and complaints, but not to refractive errors. In this case report, we present ethnically diverse patients who reported asthenopic symptoms shortly after recovering from COVID-19 infection. The hyperopic shift in the refractive error, post-COVID could indicate the ciliary body muscle's inability to sustain accommodation, resulting in asthenopia. Hence, refractive errors should also be considered as a post-COVID complication, even if the magnitude is small, especially when patients have a headache and other asthenopic symptoms. Performing dynamic retinoscopy and cycloplegic refraction will also aid in the better management of these patients.

Correlation between bilateral lateral rectus muscle recession and myopic progression in children with intermittent exotropia

Although several studies have reported about the relationship between the surgical correction of intermittent exotropia and myopic progression, it remains unclear, unlike the relationship between esotropia and hyperopia. Thus, this retrospective case control study evaluated the impact of bilateral lateral rectus recession in intermittent exotropia on myopic progression. This study included 388 patients with intermittent exotropia. The refractive errors and degree of exodeviation at each follow up period were analyzed. The rate of myopic progression was -0.46 ± 0.62 diopter (D)/year in patients who underwent surgery and -0.58 ± 0.78 D/year in patients who did not, with no significant difference between them (p = 0.254). Patients who had recurrences of more than 10 prism diopters were compared with patients who did not have. The rate of myopic progression was -0.57 ± 0.72 D/year in the recurrent group and -0.44 ± 0.61 D/year in the non-recurrent group, with no significant difference between them (p = 0.237). Patients with fast myopic progression had more recurrence than patients with slow progression (p = 0.042). Moreover, recurrence had a positive correlation with fast myopic progression (OR = 2.537, p = 0.021). Conclusively, the surgical correction of intermittent exotropia did not influence myopic progression.

Patients with Intermittent Exotropia and Exophoria Exhibit Non-aggravated Lens Decentration After Orthokeratology Application: The Nanjing Strabismus Cohort

INTRODUCTION

There is a high prevalence of intermittent exotropia and exophoria in myopic populations, and orthokeratology is one of the effective interventions to control myopia progression in children. However, it is still obscure whether intermittent exotropia and exophoria children could wear orthokeratology without experiencing aggravated lens decentration.

METHODS

This was a multi-center, prospective cohort study. A total of 123 myopic participants aged 8-14 years were recruited, where conditions of deviation included intermittent exotropia, exophoria, and orthophoria. Uncorrected visual acuity and corneal topography data were obtained at baseline and after 1 month of wearing orthokeratology lens. Lens decentration was analyzed in a MATLAB program. Magnitude of deviation and refractive errors were evaluated prior to orthokeratology treatment. Fisher's exact test, ANOVA test, and univariate and multivariate linear regression models were established to evaluate the role of magnitude of deviation in lens decentration.

RESULTS

There was no significant difference in magnitude and direction of lens decentration among three groups (magnitude: F = 1.25, P = 0.289; direction: Fisher = 9.91, P = 0.078). According to scale division of decentration, 1 (2.6%) intermittent exotropia subject, 2 (3.8%) exophoria subjects, and 1 (3.0%) orthophoria subject experienced severe decentration (Fisher = 1.10, P = 0.947). Inferotemporal decentration was most common among all subjects (intermittent exotropia 50.0%, exophoria 76.9%, orthophoria 72.7%). Univariate and multivariate linear regression analyses revealed that magnitude of deviation was not an independent risk factor for lens decentration [β = -0.00, 95% confidence interval (CI) -0.01-0.00, P = 0.180], while surface asymmetry index (SAI) (β = 0.21, 95% CI 0.02-0.40, P = 0.028) and surface regularity index (SRI) (β = -0.39, 95% CI -0.66 to -0.13, P = 0.004) had significant correlation with polar decentration.

CONCLUSION

Patients with intermittent exotropia and exophoria exhibit non-aggravated lens decentration after orthokeratology application. Thus, lens decentration is not the concern for orthokeratology prescription.

Accommodative responses under various viewing conditions in surgical patients with intermittent exotropia: an institutional, retrospective study

Purpose

To investigate the difference of spherical equivalent (SE) and pupil diameter in adult patients with intermittent exotropia (IXT) under various viewing conditions before and after surgery.

Methods

We retrospectively analyzed the medical records of 23 adult patients who underwent a surgery for IXT. The angle of deviation was measured by the prism and alternative cover test. Refractive error and pupil diameter were measured using the Grand Seiko WAM-5500 open-field autorefractor under binocular and monocular viewing conditions when patients stared at distance (6 m) and near (33 cm). Regression analyses were performed between accommodative load and the angle of deviation.

Results

Twenty-three patients (10 males, 13 females) with a mean age of 31.17±8.95 years, of whom 13 (56.5%) had the right eye as the dominant eye. The mean angle of deviation at near and at distance was 69.57±26.37 and 65.43±28.92 prism diopters respectively. There were no significant differences in accommodative response and pupil diameter between the dominant and non-dominant eyes. SE decreased when patients changed from monocular to binocular viewing, and from distant to near viewing (all P< 0.05), so as the pupil diameter (all P< 0.001). During binocular, not monocular viewing, SE was significantly greater after operation than it was before operation (P< 0.001). Accommodative load and pupillary constriction narrowed (p< 0.001) after the operation. Linear regression analysis showed a correlation between the angle of deviation at distance and accommodative load at distance (r²=0.278, p=0.010) and at near (r²=0.332, p=0.005).

Conclusion

In order to maintain ocular alignment, patients with IXT suffer a large accommodative load, which is related to the angle of deviation. Surgery helps eliminating extra accommodation.

Inter-eye Differences in Ocular Biometric Parameters of Concomitant Exotropia

Purpose: To evaluate the ocular biometric parameters in patients with constant and intermittent exotropia by the measurement of swept-source optical coherence tomography (SS-OCT) optical biometer OA-2000 and comparing it with the normal control subjects. Design: Cross-sectional case-control study. Participants: Fifty-five constant and 24 intermittent patients with exotropia with central fixation and 77 orthotropic normal control participants aged 4-18 years old. Methods: Non-contact and high-resolution optical biometric OA-2000 measurements were conducted under uniform ambient light conditions. The statistical analysis included intraclass correlation coefficient (ICC), Bland-Altman plot, and independent t-tests. Main Outcome Measures: Spherical equivalent (SE), ocular biological parameters such as pupil diameter (PD), anterior chamber depth (ACD), lens thickness (LT), and axial lengths (AL). The absolute values of inter-eye differences for SE, PD, ACD, LT, and AL were recorded as AnisoSE, AnisoPD, AnisoACD, AnisoLT, and AnisoAL, respectively. Results: AnisoSE (0.878 vs. 0.577, P = 0.019), AnisoAL (0.395 vs. 0.208, P = 0.001), AnisoACD (0.060 vs. 0.032, P < 0.001), AnisoLT (0.060 vs. 0.031, P = 0.002), and AnisoPD (0.557 vs. 0.340, P = 0.002) were significantly larger in concomitant patients with exotropia. The SE, AL, ACD, LT, and PD showed excellent binocular correlation with ICC values that ranged from 0.943 to 0.987 in control participants and from 0.767 to 0.955 in concomitant exotropia patients. Bland-Altman plots showed the wider range of agreement in patients with concomitant exotropia than the control participants (SE: 5.0288 vs. 3.3258; AL: 2.2146 vs. 1.3172; ACD:0.3243 vs. 0.1682; PD: 2.4691 vs. 1.9241; and LT:0.3723 vs 0.1858). Conclusion: Patients with concomitant exotropia showed larger inter-eye differences in SE, ACD, LT, PD, and AL. Advice should be given to suspicious children to avoid or delay the development of concomitant exotropia.

Longitudinal Rehabilitation of Binocular Function in Adolescent Intermittent Exotropia After Successful Corrective Surgery

PURPOSE

To study the longitudinal rehabilitation of binocular visual function in adolescent intermittent exotropia (IXT) after successful surgery and compare the results with those of a normal population. The role of binocular function in ocular alignment stability was also evaluated postoperatively.

METHODS

In this prospective study, 30 adolescents with IXT successfully corrected after 1 month were followed for 12 months, and 30 children with normal vision were enrolled as controls. Stereopsis, the fusional vergence amplitude, sensory fusion, and accommodative flexibility were measured to assess binocular function at baseline and 6 and 12 months postoperatively. The controls were tested once when they were enrolled in the study.

RESULTS

The deviation was -32.00 ± 8.60 prism diopters (PD) at distance fixation and -36.0 ± 9.10 PD at near fixation preoperatively with an average correction of 28.53 ± 3.79 PD and 30.67 ± 1.34 PD at 1 month postoperatively. Distance stereoacuity and near stereoacuity improved from 1 to 12 months postoperatively (p = 0.025 and p = 0.041, respectively). Compared with the controls, the fusional convergence reserve at distance (p = 0.025) and near (p = 0.033) fixations and fusion reserve ratio at distance (p = 0.000) and near (p = 0.000) fixations remained subnormal, whereas sensory fusion (p = 0.237), distance stereopsis (p = 0.120), and the fusional divergence amplitude at a distance (p = 0.168) were normal. However, no significant correlations were found between binocular functions at 1 month postoperatively and the postoperative drift.

CONCLUSION

Binocular function significantly improved from before to after successful corrective surgery and continued to improve from 1 to 12 months postoperatively in adolescents with IXT. No significant correlations were found between binocular functions at 1 month postoperatively and ocular alignment stability.

Study on Binocular Accommodative Function in Children With Different Types of Intermittent Exotropia

Objective: This study aims to investigate the monocular and binocular accommodative amplitude (AMP) and accommodative function (AF) in children with different types of intermittent exotropia (IXT). Methods: A total of 40 children with IXT were enrolled in the study. Monocular and binocular AMP and AF were measured using the modified approach method and the ±2D flip method, and the differences between the fixing and non-fixing eyes of non-strabismic children and children with different types of IXT were compared. Results: The AMP of the fixing eyes of children with IXT was lower than that of their non-fixing eyes (p = 0.007). Conversely, the AF was higher in the fixing eyes than in the non-fixing eyes (p < 0.001). The AMPs of each group of children with IXT were lower than those of the control group, while the AMP of the group with convergence insufficiency was lower than that of the other two groups with IXT. In addition, the AF of the group with convergence insufficiency was lower than that of the group with basic exotropia and the control group (p < 0.05). Conclusion: There is a difference in accommodation between the fixing and non-fixing eyes of children with IXT, and the degree of variation depends on the type of IXT. Moreover, the binocular accommodative function of children with IXT is lower than that of non-strabismic children.

Difference in myopia progression between dominant and non-dominant eye in patients with intermittent exotropia

OBJECTIVE

To investigate the difference in the rate of myopia progression between the dominant and non-dominant eye in patients with intermittent exotropia (IXT).

METHODS

We retrospectively reviewed the medical records of 33 patients who underwent surgery and later reoperation for IXT. We included only patients whose spherical equivalent refractive errors (SER) were ≤ - 0.50 diopter (D) in at least one eye at the time of reoperation. The main outcome measurement was the rate of myopia progression, which was defined as the mean annual change in SER between the first and second surgery. We classified patients into two groups: group A, which comprised 25 patients whose non-dominant eyes showed a faster myopia progression than their dominant eyes, and group B, which comprised the remaining 8 patients showing the opposite.

RESULTS

Mean age of the patients at the time of the initial surgery was 5.64 years. Mean interval between the initial and second surgery was 4.45 years. Mean rate of myopia progression over the interval was - 0.37 D/year in the dominant eyes and - 0.50 D/year in the non-dominant eyes (P < 0.001). Group A had a significantly greater amount of distance deviation (31.0 vs. 25.6 PD, P = 0.020) and near deviation (30.8 vs 26.0 PD, P = 0.039) before the initial surgery and a significantly worse score of distance control (3.05 vs. 2.00, P = 0.023) before the second surgery than group B.

CONCLUSIONS

The non-dominant eyes experienced a faster myopia progression than the dominant eyes in patients with IXT. This faster myopia progression demonstrated in the non-dominant eyes was associated with clinically severe exotropia in terms of the amount of deviation and the degree of control.

Insufficient accommodation during binocular near viewing in eyes with intermittent exotropia

PURPOSE

To investigate the changes in spherical equivalent and pupil response during near viewing in patients with intermittent exotropia (IXT) who have complaints of blurred vision or asthenopia from near viewing in daily life using a novel binocular wavefront aberrometer.

STUDY DESIGN

A cross-sectional study.

METHODS

Ten IXT patients and ten healthy subjects wearing full-correction lenses at far sight (5 m) were instructed to fixate on a near target at 67 cm, which was then moved to 40 cm three times. Serial changes in the spherical equivalent (SE) refractive error (SE) were measured during this task using a laboratory-made open-field binocular Hartmann-Shack wavefront aberrometer and compared between patients and healthy subjects. In the IXT patients, regression analysis was performed between ∆SE and exodeviation angles, as measured by an alternate prism and cover test. Pupil-diameter and pupil-constriction ratios were also compared between patients and healthy subjects, and the correlation of constriction ratio with ∆SE was calculated for both groups.

RESULTS

Compared to healthy subjects, IXT patients demonstrated significantly lower ∆SE of convergence (mean ± SD, 0.91 ± 0.26 D vs. 1.15 ± 0.19 D; P < 0.05) and divergence (0.93 ± 0.28 D vs. 1.16 ± 0.20 D; P < 0.05). Angle of exotropia was negatively correlated with ∆SE during far-sight and near-sight convergence and divergence (P < 0.05). Pupil-constriction ratio was also reduced in patients compared to healthy subjects (6.67% ± 3.31% vs. 11.9% ± 5.96%; P<0.05). Pupil-constriction ratio was positively correlated with ∆SE during convergence in both groups (P < 0.05).

CONCLUSION

Insufficient accommodation and pupil constriction during near viewing were observed in patients with IXT who had complaints of blurred vision or asthenopia from near viewing. These conditions might contribute to symptoms, such as fatigue, eye strain and impaired visual performance.