Intermittent Exotropia and Accommodative Esotropia: Distinct Disorders or Two Ends of a Spectrum?

Clinical characteristics and treatment outcomes of myopic children and adolescents with acute acquired comitant esotropia

CLINICAL RELEVANCE

Acute acquired comitant esotropia (AACE) is becoming increasingly common in young children. Understanding clinical characteristics and treatment outcomes can inform future practice.

BACKGROUND

To evaluate clinical characteristics of myopic children and adolescents with AACE, and the outcomes of varying treatments.

METHODS

A retrospective review of medical records was conducted to identify patients diagnosed with AACE and diplopia between 2016 and 2020. The duration of smartphone use, angle of deviation, refractive error, stereopsis, and treatment options were analysed. The motor outcomes were evaluated at the earliest 6-month postoperative visit (6-30 months), and orthotropia or esodeviation ≤10 prism dioptres (PD) was defined as success. Successful sensory outcomes were defined as the elimination of diplopia in primary gaze or the presence of stereoacuity.

RESULTS

Twelve patients diagnosed with AACE were identified. Ages were between 9 and 19 years (15.6 ± 3.3 years). All patients showed convergent and comitant esotropia ranging from 12 to 40 PD at distance fixation that was nearly equivalent for distance and near fixation. The mean age at the initial visit was 15.6 ± 3.3 years. Post-treatment esodeviations were significantly lower at both distance and near compared to pretreatment (p < 0.001, for both). Eight patients required surgery and were treated with bilateral medial rectus muscle recession, two patients were treated with botulinum toxin, and two patients were followed with prismatic glasses. Nine of 10 patients (%90) treated with either surgery or botulinum toxin had successful motor and sensory outcomes.

CONCLUSIONS

Surgery is the most efficient treatment option; botulinum toxin and prismatic glasses could be useful treatment options in patients who refuse to have surgery or for whom the amount of deviation is small and variable.

Epidemiology, clinical features, and surgical outcomes of acute acquired concomitant esotropia associated with myopia

PURPOSE

To analyze epidemiology, clinical features, and surgical outcomes of type III acute acquired concomitant esotropia (Bielschowsky esotropia (BE)).

METHODS

The medical charts of patients diagnosed with acquired concomitant esotropia between 2013 and 2021 were reviewed. Assessed data were age, gender, age at diplopia onset, age at the diagnosis, refraction, visual acuity, neuroimaging, diplopia onset, angle of deviation, stereopsis, surgical procedure, amount of surgery, and relapse of diplopia after surgery. Moreover, we investigated the correlation between the use of electronic devices and the onset of diplopia.

RESULTS

One hundred seventeen patients (mean age 35.07 ± 15.81 years) were included in the study. The mean delay to the diagnosis was 3.29 ± 3.62 years. Myopia range was 0 to 17 diopters spherical equivalent. 66,3% spent more than 4 hours a day using laptops, tablets, or smartphones at the onset of diplopia, and 90,6% presented a subacute onset. None showed neurologic signs or symptoms. Patients who underwent surgery were ninety-three, with a rate of surgical success of 93.6%, and a relapse rate of 17.2%. A negative correlation resulted between pre-operative deviation and age at diagnosis (ρ = -0.261; p<0.05), whereas factors associated with surgical failure were older age at diplopia onset (p = 0.042) and longer delay between onset and diagnosis (p = 0.002).

CONCLUSION

We registered an outstanding increase in prevalence of BE, which could be related to the exponential increase in the use of electronic devices for professional, educational, and recreational purposes. A prompt diagnosis and an augmented dose of surgery allows good motor and sensory results.

Functional changes in the visual cortex in preoperative and postoperative patients with intermittent exotropia: study protocol for a non-randomised case-control clinical trial

INTRODUCTION

Intermittent exotropia (IXT) is the most common type of divergent squint. IXT is primarily a cortical neurologic dysfunction disorder, occurring as a result of the insufficient maintenance of sensory and motor fusion. Recent reports have demonstrated the relationship between IXT and visual cortical impairment. We planned to assess blood oxygen level-dependent (BOLD)-functional magnetic resonance imaging (fMRI) in patients with IXT during the preoperative and postoperative follow-ups to evaluate the functional changes in the visual cortex.

METHODS AND ANALYSIS

A total of 90 Chinese subjects will be recruited, and their ages will be between 18 and 40 years old. The subjects will include the surgical treatment (ST) group (45 subjects with IXT who will undergo surgery) and the HC group (45 age-matched, sex-matched and education-matched healthy volunteers). The assessments will include the following aspects: fMRI and general ophthalmic examinations, optometry measurements and strabismus-related tests, such as the ocular deviation, binocular vision test and Newcastle Control Score (NCS). Each subject will complete the resting-state BOLD-fMRI, and the sequences will include echo planar imaging (EPI) pulse and 3-dimensional brain volume (3D-BRAVO) to acquire high-resolution images. The follow-up schedule will be 6 and 12 months after the surgery. The primary outcome will be determined by cortex changes in BOLD-fMRI in the ST group before and after surgery. We will also compare the HC group with the preoperative subjects in the ST group. The secondary outcomes will be changes in strabismus-related examinations, such as binocular visual function and NCS.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Medical Ethics Committee of Beijing Tongren Hospital. We plan to publish the results of this study in a peer-reviewed journal article.

TRIAL REGISTRATION NUMBER

ChiCTR2100048852.

Altered Spontaneous Brain Activity Patterns and Functional Connectivity in Adults With Intermittent Exotropia: A Resting-State fMRI Study

The purpose of this study is to investigate brain functional changes in patients with intermittent exotropia (IXT) by analyzing the amplitude of low-frequency fluctuation (ALFF) of brain activity and functional connectivity (FC) using resting-state functional magnetic resonance imaging (rs-fMRI). There were 26 IXT patients and 22 age-, sex-, education-, and handedness-matched healthy controls (HCs) enrolled who underwent rs-fMRI. The ALFF, fractional ALFF (fALFF) values in the slow 4 and slow 5 bands, and FC values were calculated and compared. The correlations between ALFF/fALFF values in discrepant brain regions and clinical features were evaluated. Compared with HCs, ALFF/fALFF values were significantly increased in the right angular gyrus (ANG), supramarginal gyrus (SMG), inferior parietal lobule (IPL), precentral gyrus (PreCG), and the bilateral inferior frontal gyri (IFG), and decreased in the right precuneus gyrus (PCUN), left middle occipital gyrus (MOG), and postcentral gyrus (PoCG) in IXT patients. The Newcastle Control Test score was negatively correlated with ALFF values in the right IFG (r = −0.738, p < 0.001). The duration of IXT was negatively correlated with ALFF values in the right ANG (r = −0.457, p = 0.049). Widespread increases in FC were observed between brain regions, mainly including the right cuneus (CUN), left superior parietal lobule (SPL), right rolandic operculum (ROL), left middle temporal gyrus (MTG), left IFG, left median cingulate gyrus (DCG), left PoCG, right PreCG, and left paracentral gyrus (PCL) in patients with IXT. No decreased FC was observed. Patients with IXT exhibited aberrant intrinsic brain activities and FC in vision- and eye movement-related brain regions, which extend current understanding of the neuropathological mechanisms underlying visual and oculomotor impairments in IXT patients.

Decreased Functional Connectivity of the Primary Visual Cortex and the Correlation With Clinical Features in Patients With Intermittent Exotropia

The purpose of this study is to investigate characteristic alterations of functional connectivity (FC) patterns in the primary visual area (V1) in patients with intermittent exotropia (IXT) using resting-state functional magnetic resonance imaging (rs-fMRI) and how they relate to clinical features. Twenty-six IXT patients and 21 age-, sex-, handedness-, and education-matched healthy controls (HCs) underwent rs-fMRI. We performed FC analyses between bilateral V1 and other brain areas and compared FC strength between two groups. A Pearson correlation analysis was used to evaluate the correlation between the FC differences and clinical features. Compared with HCs, patients with IXT showed significantly lower FC of the right V1 with the right calcarine sulcus and right superior occipital gyrus, and the left V1 with right cuneus and right postcentral gyrus. The Newcastle Control Test score was positively correlated with mean FC values between the left inferior parietal lobule and bilateral V1, and between the left supramarginal gyrus and left V1. The duration of IXT was positively correlated with mean FC values between the right inferior occipital gyrus and right V1. Reduced FC between the V1 and various brain regions involved in vision and eye movement processes may be associated with the underlying neural mechanisms of impaired visual function in patients with IXT.

Change in the eye position under general anesthesia in children with intermittent exotropia

PURPOSE

To evaluate the eye position in subjects with intermittent exotropia and normal subjects under general anesthesia (GA) using the strabismus photo analyzer.

METHODS

This retrospective case-control study included 78 subjects with intermittent exotropia and 25 normal control subjects who underwent epiblepharon surgery. Eye position under GA was assessed using the strabismus photo analyzer, based on eye models generated from corneal lights and limbus in pre- and post-anesthesia images. Eye positions under GA in the control and intermittent exotropia groups were compared. Preoperative angle of deviation was also compared with amount of change in eye position under GA in the intermittent exotropia group.

RESULTS

Eye position under GA was more divergent in subjects with intermittent exotropia than in controls (P = 0.008). The amount of change in eye position under GA was correlated with the preoperative angle of deviation (r² = 0.47; P < 0.001). In small preoperative exodeviations, the change in eye position was primarily more divergent, whereas in large exodeviations, a convergent tendency-less exotropic compared with the preoperative angle of exodeviation-was observed.

CONCLUSIONS

In subjects with small preoperative exodeviations, there was a tendency for eye position to become more divergent after GA; in those with large exodeviations, there was less exotropia after GA.

Risk factors for spontaneous consecutive exotropia in children with refractive and nonrefractive accommodative esotropia

PURPOSE

To investigate the risk factors for development of spontaneous consecutive exotropia (ScXT) among patients with refractive and nonrefractive accommodative esotropia (AET).

STUDY DESIGN

Retrospective.

METHODS

Patients who were diagnosed with AET were reviewed from January, 2000 to December, 2016. The patients who developed ScXT after well corrected hyperopia were defined as exodeviation group (n = 51), and the patients who did not show exodeviation and were well controlled with eyeglasses were defined as the control group (n = 117). The changes in cycloplegic refraction, mean angle deviation at initial visit, time till the first correction of esodeviation, presence of amblyopia and accompanying strabismus were compared between the two groups.

RESULTS

The mean interval from the first visit to correction of esodeviation under 8 PD in the exodeviation group was shorter than of the control group (P = 0.008). Patients in the exodeviation group showed more dissociated vertical deviation (DVD) (P = 0.015) and faster reduction in hyperopia per year (more hyperopic eye: P = 0.006; less hyperopic eye: P = 0.034) than the patients in the control group. Exodeviation was found mean 42.31 ± 41.13 months after hyperopia correction. There were no differences in angle deviation at initial visit, and presence of amblyopia.

CONCLUSION

ScXT can be found in AET with faster reduction in hyperopia per year, accompanied by DVD, or in eyes with esodeviation corrected in relatively shorter time. It can be noted even in patients with good alignment over a long-term, so long-term follow-up is recommended.

Phoria Adaptation: The Ghost in the Machine

Importance: Phoria adaptation is a central tonus mechanism that provides plasticity to binocular alignment. However, its slow dissipation inevitably adulterates our clinical strabismus measurements.Purpose: To examine the role of phoria adaptation in normal binocular control, understand its neural substrate, and explore how it can alter our clinical measurements in common forms of strabismus.Methods: Investigation into the role of phoria adaptation in maintaining binocular alignment and its role in altering clinical strabismus measurement.Results: Phoria adaptation permeates all aspects of binocular alignment. It accounts for the stability of orthophoria, "latent" phorias, tenacious proximal fusion in intermittent exotropia, large fusional vertical amplitudes in congenital superior oblique muscle palsy, the "eating up" of prisms in accommodative esotropia, the smaller measured distance deviation in patients with high AC/A ratio or convergence excess, absence of physiologic skew deviation during head tilt, fusional divergence amplitudes, and spread of comitance. This binocular control system probably arises from a cerebellar learning mechanism that involves input via climbing fibers to the inferior olive, which provide a powerful timing and error signal to the cerebellar Purkinje cells to produce activity-dependent modification analogous to long-term potentiation.Conclusions: Phoria adaptation is generated by a central neural integrator that provides inertia, plasticity, and positional stability to human binocular vision.

Clinical characteristics and surgical outcomes of adults with acute acquired comitant esotropia

PURPOSE

To investigate clinical characteristics of adults with acute acquired comitant esotropia and to evaluate the muscle recession amount needed to achieve a favorable outcome after performing medial rectus muscle recession.

STUDY DESIGNS

Retrospective study.

METHODS

Patients diagnosed with acute acquired comitant esotropia, who underwent medial rectus muscle recession with adjustable suture between 2008 and 2016 were included. Surgical outcomes were classified into motor and sensory. The motor outcomes were evaluated at the 1-year postoperative visit and divided into success (orthotropia or esodeviation ≤ 8 PD) and failure (esodeviation > 8 PD). The successful sensory outcomes were defined as elimination of diplopia in primary gaze. Factors including age, sex, refractive error, deviation angle, and surgical amount were compared between groups.

RESULTS

Sixteen subjects were included whose mean (± SD) age at the initial visit was 27.5 ± 11.0 years. Mean preoperative maximum angle of deviation was 27.9 ± 9.3 PD at distance and 28.6 ± 12.0 PD at near. Mean refractive error was -2.55 ± 2.92 D. Twelve of 16 subjects (75%) had successful motor and sensory outcomes. Age, sex, refractive error and deviation angle were not different between the two groups. Both success and failure groups required a greater amount of medial rectus muscle recession than those indicated by the Parks' surgical table, with a 40.6 ± 25.8 % augmentation in the success and 7.9 ± 6.9 % in the failure group (P = .028).

CONCLUSIONS

To achieve better surgical outcomes in adults with acute acquired comitant esotropia, targeting postoperative orthotropia by increasing the amount of medial rectus muscle recession is recommended.

Subnormal Binocular Contrast Sensitivity Summation in Patients with Intermittent Exotropia

BACKGROUND

To evaluate binocular summation ratio using contrast sensitivity (CS) testing and correlation between binocular summation and stereoacuity, and control scale in intermittent exotropia (IXT).

METHODS

We conducted a prospective case-control study. Thirty-seven IXT and 41 controls were evaluated with both monocular and binocular CS testing. We compared the binocular summation ratio of IXT to that of controls. Near and distance stereoacuity was assessed and office-based control scale was evaluated. We investigated correlation between binocular CS summation ratio and stereoacuity, and control scale in IXT, respectively.

RESULTS

IXT had lower binocular CS summation ratio than controls at 1.5 and 3.0 cycles/degree (1.01 ± 1.02 vs. 1.62 ± 1.88 and 1.17 ± 0.96 vs. 1.86 ± 1.75, Both P < 0.05). We found significant correlation between binocular CS summation ratio at 3.0 cycles/degree and both near and distance stereoacuity (r = -0.411, P = 0.012 and r = -0.624, P = 0.005), and ratio at 1.5 cycles/degree also correlated significantly with distance stereoacuity (r = -0.397, P = 0.034) in the IXT. Binocular CS summation ratio was correlated to control scale at 1.5 and 3.0 cycles/degree (r = -0.327, P = 0.041 and r = -0.418, P = 0.028), and the ratio significantly differed in control scale groupings analysis at the same frequencies (Both P < 0.05).

CONCLUSION

Our findings of subnormal binocular CS summation ratio in IXT had correlation with stereoacuity and control scale suggest that binocular CS testing may be a useful method in assessing binocular visual function in IXT.

The Effect of Prism Adaptation on the Angle of Deviation in Convergence Excess Esotropia and Possible Consequences for Surgical Planning

Convergence excess esotropia describes a heterophoria with binocular single vision (BSV) on distance viewing that becomes esotropic on accommodation upon near fixation. Prism adaptation test (PAT) is a procedure routinely used to reveal the maximum angle of deviation preoperatively for many types of strabismus and has been shown to improve surgical outcomes; however, it is not conventionally used for convergence excess esotropia.

AIM

This study compares the angle of deviation at 1/3 m and 6 m before and after prism adaptation in subjects with convergence excess esotropia to determine if a masked distance angle of deviation can be demonstrated similar to the masked near angle of deviation in some intermittent exotropes. Surgical results are reported.

RESULTS

Fifty-eight children with convergence excess esotropia were prescribed prism adaptation prior to strabismus surgery and 49 met the inclusion criteria. A median increase in the angle of deviation of 20 prism dioptres (PD) was seen at both 1/3 m and 6 m following PAT. These changes were statistically significant (p < 0.001) at both distances. Following one surgical procedure, 83.6% were fully binocular postoperatively.

CONCLUSION

Prism adaptation frequently reveals an otherwise masked large distance angle of deviation in convergence excess esotropia. Convergence excess esotropia can be subdivided into two categories: true and simulated. Those with true convergence excess exhibit a manifest convergent strabismus when viewing a close object and a small, well-controlled latent strabismus upon fixation of a distant object. Those with simulated convergence excess have a comparable near deviation to those with true convergence excess but can be shown to have a distance deviation that approaches the size of the near strabismus once the normal fusional mechanisms are disrupted by a period of prism adaptation.

Capturing the Moment of Fusion Loss in Intermittent Exotropia

PURPOSE

To characterize eye movements made by patients with intermittent exotropia when fusion loss occurs spontaneously and to compare them with those induced by covering 1 eye and with strategies used to recover fusion.

DESIGN

Prospective study of a patient cohort referred to our laboratory.

PARTICIPANTS

Thirteen patients with typical findings of intermittent exotropia who experienced frequent spontaneous loss of fusion.

METHODS

The position of each eye was recorded with a video eye tracker under infrared illumination while fixating on a small central near target.

MAIN OUTCOME MEASURES

Eye position and peak velocity measured during spontaneous loss of fusion, shutter-induced loss of fusion, and recovery of fusion.

RESULTS

In 10 of 13 subjects, the eye movement made after spontaneous loss of fusion was indistinguishable from that induced by covering 1 eye. It reached 90% of full amplitude in a mean of 1.75 seconds. Peak velocity of the deviating eye's movement was highly correlated for spontaneous and shutter-induced events. Peak velocity was also proportional to exotropia amplitude. Recovery of fusion was more rapid than loss of fusion, and often was accompanied by interjection of a disconjugate saccade.

CONCLUSIONS

Loss of fusion in intermittent exotropia is not influenced by visual feedback. Excessive divergence tone may be responsible, but breakdown of alignment occurs via a unique, pathological type of eye movement that differs from a normal, physiological divergence eye movement.

Assessment of Cortical Dysfunction in Patients with Intermittent Exotropia: An fMRI Study

Neural imaging studies have found the connection between strabismus and brain cortex. However, the pathological mechanisms of intermittent exotropia are still not fully understood. In the present study, changes of binocular fusion related cortices in intermittent exotropia were investigated with blood oxygen level dependent functional magnetic resonance imaging. Activated cortices induced by fusion stimulus were found to be distributed in several regions such as bilateral middle occipital gyrus, bilateral middle temporal gyrus, left superior parietal lobule and so on. Compared with normal subjects, the increased activation intensity was observed in bilateral superior parietal lobule and inferior parietal lobule in subjects with intermittent exotropia. These findings indicate that binocular fusion involves a complicated brain network including several regions. And cortical activities of bilateral superior parietal lobule and inferior parietal lobule compensate for the binocular fusion dysfunction in intermittent exotropia.

Stability of human binocular alignment in the dark and under conditions of nonfixation

PURPOSE

To evaluate the stability of human binocular alignment under conditions of altered fixation and luminance.

METHODS

Horizontal binocular alignment in 8 healthy orthotropic subjects was measured using infrared video-oculography (VOG) under conditions of binocular fixation and luminance change. Each testing condition was preceded by a binocular fixation period in room light (475 lux) to define the baseline binocular alignment. Binocular alignment was then measured in darkness without fixation, in room light through a semitranslucent filter that precluded fixation, and in darkness with a distant fixational target. We used the signed rank test to determine statistically whether these experimental conditions induced significant binocular alignment change from each baseline binocular alignment.

RESULTS

The mean horizontal binocular alignment in the dark without fixation was similar to baseline binocular alignment (0.2° ± 2.8°; P = 0.4). The mean horizontal binocular alignment without fixation in room light was also similar to baseline binocular alignment (-1.4° ± 1.6°; P = 0.08). The mean horizontal binocular alignment in the dark when a fixational target was provided showed an exodrift compared to baseline alignment (2.3° ± 1.0°; P = 0.0004).

CONCLUSIONS

The human brain does not require visual input to maintain binocular alignment on a short-term basis. The resilience of binocular alignment probably reflects the presence of phoria adaptation.

Variability of Ocular Deviation in Strabismus

IMPORTANCE

In strabismus, the fixating eye conveys the direction of gaze while the fellow eye points at a peripheral location in space. The stability of the eyes may be reduced by the absence of a common target.

OBJECTIVE

To quantify the stability of eye position in strabismus and to measure variability in the ocular deviation.

DESIGN, SETTING, AND PARTICIPANTS

From 2010 to 2014, a prospective comparative case study of 25 patients with alternating exotropia with normal visual acuity in each eye and 25 control individuals was conducted in a laboratory at a tertiary eye center. A video eye tracker was used to measure the position of each eye while participants alternated fixation on the center of a cross under dichoptic conditions or scanned pictures of natural scenes.

MAIN OUTCOMES AND MEASURES

Spatial and temporal variability in the position of the fixating eye and the nonfixating eye in patients with strabismus and control individuals, quantified by the log area of ellipses containing 95% of eye positions or mean SDs of eye position.

RESULTS

In the 25 patients with strabismus, the mean (SD) age was 28 (14) years (range, 8-55 years) and the mean (SD) ocular deviation was 14.2° (5.9°) (range, 4.4°-22.4°). In the patients with strabismus, the mean position variability (1.80 log units; 95% CI, 1.66-1.93) for the deviating eye was greater than for the fixating eye (1.26 log units; 95% CI, 1.17-1.35) (P < .001). The fixating eye of patients with strabismus was more variable in position than the fixating eye of individuals without strabismus (0.98 log units; 95% CI, 0.88-1.08) (P < .005).

CONCLUSIONS AND RELEVANCE

In patients with strabismus, even without amblyopia, the deviated eye is more variable in position than the fixating eye. Both eyes are less stable in position than the eyes of control individuals, which indicates that strabismus impairs the ability to fixate targets steadily. Saccades contribute to variability of the deviation angle because they are less conjugate in patients with strabismus.