Sensory eye balance in surgically corrected intermittent exotropes with normal stereopsis

Binocular Visual Deficits at Low to High Spatial Frequency in Intermittent Exotropia After Surgery

Purpose

To investigate binocular visual deficits at low to high spatial frequencies in patients with intermittent exotropia (IXT) after surgical correction, using the binocular orientation combination task.

Methods

Thirteen patients whose IXT has been aligned surgically (17 ± 4.8 years old; 7 females) and 13 normal individuals (21.8 ± 2.5 years old; 6 females) were recruited. All participants had normal or corrected-to-normal visual acuity. The IXT patients had undergone surgery at least one month prior to the study and achieved successful eye alignment post-surgery. We measured participants' balance points (BPs), defined as the interocular contrast ratio (nondominant eye/dominant eye) when both eyes contributed equally to binocular combination, using the binocular orientation combination task at three spatial frequencies (0.5, 4.0, and 8.0 cycles/degree). The absolute values of log10(BP) (i.e., |logBP|) and the area under of the |logBP| versus spatial frequency curve were used to quantify the extent of binocular imbalance.

Results

Surgery aligned the eye position of patients with IXT, with a postoperative exodeviation of -4.92 ± 4.29 prism diopters at distance. Participants' |logBP| values showed significant differences between groups, F(1,24) = 9.175, P = 0.006, and across spatial frequencies, F(2,48) = 7.127, P = 0.002. However, the interaction between group and spatial frequency was not significant, F(2,48) = 0.379, P = 0.687.

Conclusions

Patients whose IXT has been alighted surgically experience binocular imbalance across a wide range of spatial frequencies, with greater binocular imbalance occurring at high spatial frequencies than low spatial frequencies.

Effect of surgery on sensory eye balance in patients with intermittent exotropia: An observational study

To evaluate the impact of strabismus surgery on sensory eye balance in patients with intermittent exotropia (IXT). In total, 112 IXT patients with ocular alignment at the first strabismus surgery and 34 controls were enrolled from January 2015 to December 2016 in this retrospective study. The effective contrast ratio (ECR) of non-dominant eyes was measured by binocular phase combination paradigm before and 3 months after surgery, and the degree of sensory eye balance was quantitatively evaluated and compared between IXT patients and controls. The preoperative and postoperative mean ECRs of IXT patients were 0.492 ± 0.182 and 0.684 ± 0.198, respectively, which were significantly lower than those of the control group (0.896 ± 0.214, both P < .001). In addition, the postoperative ECR was significantly higher than the preoperative ECR (P < .001). The ECR change was not correlated with age orstrabismus degree measured with a6 m accommodative target (both P > .05), while significant negative correlation was observed between the ECR change and strabismus degree measured with a 33 cm accommodative target (P = .002). Strabismus surgery can significantly reduce the degree of sensory eye imbalance in patients with IXT, while further treatment aimed at rebalancing the ocular dominance might be necessary for more efficient binocular visual processing in the long-term.

Cortical Reorganization After Optical Alignment in Strabismic Patients Outside of Critical Period

PURPOSE

To measure visual crowding, an essential bottleneck on object recognition and reliable psychophysical index of cortex organization, in older children and adults with horizontal concomitant strabismus before and after strabismus surgery.

METHODS

Using real-time eye tracking to ensure gaze-contingent display, we examined the peripheral visual crowding effects in older children and adults with horizontal concomitant strabismus but without amblyopia before and after strabismus surgery. Patients were asked to discriminate the orientation of the central tumbling E target letter with flankers arranged along the radial or tangential axis in the nasal or temporal hemifield at different eccentricities (5° or 10°). The critical spacing value, which is the minimum space between the target and the flankers required for correct discrimination, was obtained for comparisons before and after strabismus surgery.

RESULTS

Twelve individuals with exotropia (6 males, 21.75 ± 7.29 years, mean ± SD) and 15 individuals with esotropia (6 males, 24.13 ± 5.96 years) participated in this study. We found that strabismic individuals showed significantly larger critical spacing with nasotemporal asymmetry along the radial axis that related to the strabismus pattern, with exotropes exhibiting stronger temporal field crowding and esotropes exhibiting stronger nasal field crowding before surgical alignment. After surgery, the critical spacing was reduced and rebalanced between the nasal and temporal hemifields. Furthermore, the postoperative recovery of stereopsis was associated with the extent of nasotemporal balance of critical spacing.

CONCLUSIONS

We find that optical realignment (i.e., strabismus surgery) can normalize the enlarged visual crowding effects, a reliable psychophysical index of cortical organization, in the peripheral visual field of older children and adults with strabismus and rebalance the nasotemporal asymmetry of crowding, promoting the recovery of postoperative stereopsis. Our results indicated a potential of experience-dependent cortical organization after axial alignment even for individuals who are out of the critical period of visual development, illuminating the capacity and limitations of optics on sensory plasticity and emphasizing the importance of ocular correction for clinical practice.

Quantitative Evaluation of Binocular Visual Perception in Patients With Strabismus: An Observational Study

PURPOSE

To quantitatively evaluate and compare binocular visual perception between normal individuals and patients with different types of strabismus using a binocular phase combination paradigm.

METHODS

A total of 117 participants were included in the study and were divided into the normal control group, exophoria group, comitant exotropia group, comitant esotropia group, and special strabismus group according to the type of strabismus. The effective contrast ratio (ECR) was measured to quantitatively evaluate binocular visual perception. Binocular fusion was evaluated using the Worth 4-dots flashlight. Stereoacuity was detected by the Titmus stereo test.

RESULTS

The mean ECRs in the normal control group, exophoria group, comitant exotropia group, comitant esotropia group, and special strabismus group were 0.896 ± 0.214, 0.824 ± 0.234, 0.520 ± 0.279, 0.261 ± 0.139, and 0.461 ± 0.243, respectively. Within-group differences in the ECR were statistically significant. In addition, there was no statistically significant difference between the normal control group and exophoria group, and the concomitant exotropia group and special strabismus group and the other groups were statistically significant in pairwise comparison. The binocular visual perception was basically balanced in the exotropia group and most imbalanced in the comitant esotropia group, followed by the comitant exotropia group and the special strabismus group. The results also indicated that the decreased ECR was related to poor stereopsis and ECR had a significant positive correlation with binocular fusion function.

CONCLUSIONS

Different types of strabismus have different degrees of visual perception imbalance. The binocular phase combination paradigm applied in this study can quickly and accurately quantify the degree of binocular visual perception imbalance in patients with strabismus by measuring ECR. [J Pediatr Ophthalmol Strabismus. 2023;60(2):120-130.].

The Effects of Orthoptic Therapy on the Surgical Outcome in Children with Intermittent Exotropia: Randomised Controlled Clinical Trial

BACKGROUND

To assess the clinical effectiveness of orthoptic therapy in the postoperative stabilisation and rehabilitation of binocular function in children with intermittent exotropia (IXT) after surgery.

METHODS

This was a prospective, parallel, randomised controlled trial. A total of 136 IXT patients (aged from 7 to 17 years) who had been successfully corrected at 1 month after surgery were enrolled in this study, and 117 patients (58 controls) completed the 12-month follow-up visit. The primary outcome was established as the proportion of patients with suboptimal surgical outcomes, which were defined as: (1) exodeviation ≥10 prism diopters (PD) at distance or near using the simultaneous prism and cover test (SPCT), or (2) constant esotropia ≥6 PD at distance or near using SPCT, or (3) loss of 2 or more octaves of stereopsis from baseline. The secondary outcomes were the exodeviation at distance and near using the prism and alternate cover test (PACT), stereopsis, fusional exotropia control and convergence amplitude.

RESULTS

The cumulative probability of suboptimal surgical outcome by 12 months was 20.5% (14/68) in the orthoptic therapy group and 42.6% (29/68) in the control group. There was a significant difference between these two groups (χ² = 7.402, p = 0.007). Improvements in stereopsis, fusional exotropia control and fusional convergence amplitude were found in the orthoptic therapy group. A smaller exodrift was found in the orthoptic therapy group at near fixation (t = 2.26, p = 0.025).

CONCLUSIONS

Early postoperative orthoptic therapy can effectively improve the surgical outcome as well as stereopsis and fusional amplitude.

Sensory eye dominance following surgically correction for acute acquired concomitant esotropia of adulthood

BACKGROUND

Acute acquired concomitant esotropia (AACE) is an unusual presentation characterized by acute onset of esotropia after infancy. For patients with AACE of adulthood, the outcome of surgery, which is a common treatment, often shows successful recovery of stereopsis. However, whether surgically corrected patients with AACE of adulthood achieved balanced eyes is yet unclear.

METHODS

Here, we used a binocular phase combination paradigm to quantitatively assess the ocular dominance of 22 surgically aligned patients with AACE of adulthood, which all had regained normal stereopsis after the surgery and 14 adult controls with normal vision. The sensory eye dominance was quantified as the interocular contrast ratio, termed balance point, at which each eye contributed equally to the perception of cyclopean grating.

RESULTS

We found that, normal controls had a mean balance point value close to unity (0.96 ± 0.01), whereas adult AACE patients exhibited apparent interocular imbalance (0.76 ± 0.04), which was significantly different from control group (Mann-Whitney U = 135, P < 0.001, two tailed). In addition, the balance point of adults with AACE didn't correlate with the interval between onset of esotropia and the surgery (r =  - 0.262, p = 0.239), or the length of postoperative follow-up period (r = 0.127, p = 0.575).

CONCLUSION

Our results suggest that, for patients with AACE of adulthood whose eyes had been straightened, there is still residual sensory imbalance which may be a potential risk factor for AACE of adulthood.

Abnormal cortical morphology in children and adolescents with intermittent exotropia

Purpose

To investigate cortical differences, age-related cortical differences, and structural covariance differences between children with intermittent exotropia (IXT) and healthy controls (HCs) using high-resolution magnetic resonance imaging (MRI).

Methods

Sixteen IXT patients and 16 HCs underwent MRI using a 3-T MR scanner. FreeSurfer software was used to obtain measures of cortical volume, thickness, and surface area. Group differences in cortical thickness, volume and surface area were examined using a general linear model with intracranial volume (ICV), age and sex as covariates. Then, the age-related cortical differences between the two groups and structural covariance in abnormal morphometric changes were examined.

Results

Compared to HCs, IXT patients demonstrated significantly decreased surface area in the left primary visual cortex (PVC), and increased surface area in the left inferior temporal cortex (ITC). We also found increased cortical thickness in the left orbitofrontal cortex (OFC), right middle temporal cortex (MT), and right inferior frontal cortex (IFC). No significant differences were found in cortical volume between the two groups. There were several negative correlations between neuroanatomic measurements and age in the HC group that were not observed in the IXT group. In addition, we identified altered patterns of structural correlations across brain regions in patients with IXT.

Conclusion

To our knowledge, this study is the first to characterize the cortical morphometry of the children and adolescents with IXT. Based on our results, children and adolescents with IXT exhibited significant alterations in the PVC and association cortices, different cortical morphometric development patterns, and disrupted structural covariance across brain regions.

Altered spontaneous brain activity in patients with comitant exotropia before and after surgery: A resting-state fMRI study

Patients with comitant exotropia (CE) would usually develop compromised binocular vision and impaired stereoscopic depth perception, which could result in a profound decrease in quality of life. Although the deviated optic axis could be corrected surgically, the impaired stereovision and sensory eye balance may sometimes remain remnant. This study was to investigate the brain functional alterations in patients with CE before and after surgery, using resting-state functional magnetic resonance imaging (fMRI) with amplitude of low-frequency fluctuation (ALFF). Thirty-five patients with CE were recruited to undergo a preoperative fMRI scan, as well as 24 healthy controls (HCs). Twenty-four of the patients were available for rescanned fMRI one month after surgery. The ALFF method was used to evaluate the group differences of spontaneous brain activity. The correlations between ALFF values and clinical variables were analyzed in the patient group. Preoperatively, compared with HCs, 35 patients with CE showed significantly decreased ALFF values in one cluster involving bilateral calcarine sulcus, lingual gyrus and cuneus. The ALFF values in the above cluster were negatively correlated with disease duration (r = -0.379, P = 0.033). One month after surgery, 24 patients with available rescanned fMRI demonstrated increased ALFF values in one cluster located in bilateral cuneus, calcarine sulcus and lingual gyrus relative to the preoperative collection, while still reduced ALFF values in the cluster involving left calcarine sulcus and lingual gyrus compared with HCs. Our study revealed the functional changes of patients with CE in visual-associated brain areas before and after surgery. The findings may provide a new perspective for understanding the underlying pathological mechanisms of CE.

The predictive value of local to remote functional connectivity changes in comitant exotropia patients

BACKGROUND

Comitant exotropia (CE) is a common eye disease with abnormal eye movement, whereas altered synchronous neural activity in CE patients is poorly understood. The purpose of our study was to investigate local to remote functional connectivity of blood oxygen level-dependent (BOLD) signals changes in CE patients.

MATERIAL AND METHODS

Thirty-four patients and thirty-four healthy controls (HCs) underwent resting-state MRI scans. The ReHo and FC method was applied to investigate the local to remote functional connectivity changes in CE patients.

RESULTS

Compared to the HC group, CE patients showed significant increased ReHo values in the left cerebellar_crus2 and left middle frontal gyrus. Meanwhile, CE patients showed significant decreased ReHo values in the right middle temporal gyrus, left postcentral gyrus and right angular. Moreover, CE patients showed an increased FC between the cerebellar network, sensorimotor network (SMN) and default-mode network (DMN). The support vector machine (SVM) classification was up to a total accuracy of 94.12%. The AUC of the classification model was 0.99 on the basis of ReHo map.

CONCLUSION

Our result highlights that CE patients had abnormal local to remote functional connectivity in the cerebellar network, SMN, DMN, which might indicate the neural mechanism of eye movements and stereo vision dysfunction in CE patients. Moreover, the SVM algorithm reveals ReHo maps as a potential biomarker for predicting clinical outcomes in CE patients.

Binocular Summation Is Intact in Intermittent Exotropia After Surgery

Purpose: To determine binocular summation of surgically treated intermittent exotropia (IXT) patients by measuring the contrast threshold.

Methods: We recruited 38 surgically treated IXT patients aged 8–24 years and 20 age-matched healthy controls. All participants had normal or corrected-to-normal visual acuity (Snellen ≥ 20/20) in both eyes. The IXT patients had undergone the surgery at least a year prior to the study. Twenty-one of them obtained good alignment and 17 experienced a recurrence of exotropia. We measured the observers' monocular and binocular contrast sensitivities (CS) at six spatial frequencies (1.5, 3, 6, 12, 18, 24 cycles/degree) as an index of visual information processing at the threshold level. Binocular summation was evaluated against a baseline model of simple probability summation based on the CS at each spatial frequency and the area under the log contrast sensitivity function (AULCSF).

Results: The exo-deviation of IXTs with good alignment was −6.38 ± 3.61 prism diopters (pd) at 33 cm and −5.14 ± 4.07 pd at 5 m. For the patients with recurrence, it was −23.47 ± 5.53 pd and −21.12 ± 4.28 pd, respectively. There was no significant difference in the binocular summation ratio (BSR) between the surgically treated IXT patients, including those with good alignment and recurrence, and normal controls at each spatial frequency [F_(2,55) = 0.416, P = 0.662] and AULCSF [F_(2,55) = 0.469, P = 0.628]. In addition, the BSR was not associated with stereopsis (r = −0.151, P = 0.365).

Conclusion: Our findings of normal contrast sensitivity binocular summation ratio in IXT after surgical treatment suggest that the ability of the visual cortex in processing binocular information is intact at the contrast threshold level.

Binocular Interactions in Glaucoma Patients With Nonoverlapping Visual Field Defects: Contrast Summation, Rivalry, and Phase Combination

Purpose

In glaucoma, visual field defects in the left and right eye may be non-overlapping, resulting in an intact binocular visual field. In clinical management, these patients are often considered to have normal vision. However, visual performance also relies on binocular processing. The aim of this study was to evaluate binocular visual functions in glaucoma patients with intact binocular visual field, normal visual acuity, and stereoscopy.

Methods

We measured in 10 glaucoma patients and 12 age-similar controls: (1) monocular and binocular contrast sensitivity functions (CSF) using a modified quick CSF test to assess binocular contrast summation, (2) dominance during rivalry, and (3) contrast ratio at balance point with a binocular phase combination test. A mirror stereoscope was used to combine the left and right eye image (each 10° horizontally by 12° vertically) on a display.

Results

Area under the monocular and binocular CSF was lower in glaucoma compared to healthy (P < 0.001), but the binocular contrast summation ratio did not differ (P = 0.30). For rivalry, the percentage of time of mixed percept was 9% versus 18% (P = 0.056), the absolute difference of the percentage of time of dominance between the two eyes 19% versus 10% (P = 0.075), and the rivalry rate 8.2 versus 12.1 switches per minute (P = 0.017) for glaucoma and healthy, respectively. Median contrast ratio at balance point was 0.66 in glaucoma and 1.03 in controls (P = 0.011).

Conclusions

Binocular visual information processing deficits can be found in glaucoma patients with intact binocular visual field, normal visual acuity, and stereoscopy.

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.

Microstructural properties of major white matter tracts in constant exotropia before and after strabismus surgery

AIMS

The purpose of this study was to explore the microstructural properties of the major white matter (WM) tracts in constant exotropia (XT) before and after strabismus surgery, and further investigate the association between microstructural alterations and the ocular dominance (OD).

METHODS

We collected diffusion tensor imaging data of patients with XT before (n=19) and after (n=15) strabismus surgery and 20 healthy controls and evaluated OD and stereopsis. The probabilistic streamline tractography of the 24 major WM tracts was reconstructed by using the automated fibre quantification package. Fractional anisotropy and mean diffusivity (MD) along each tract were estimated, and their differences between the groups were examined. Furthermore, we evaluated the relationship between OD and the absolute value of altered microstructural parameters.

RESULTS

While all postoperative XT patients restored normal stereopsis, most of their OD remained aberrant (9 out of 11). Compared with that of preoperation, the MD of postoperative patients decreased significantly along left anterior thalamic radiation (ATR), left arcuate fasciculus (AF), left corticospinal tract (CST), left cingulum cingulate (CGC) and left inferior fronto-occipital fasciculus. Moreover, OD was negatively correlated with the absolute value of MD changes in left ATR, left AF, left CST and left CGC.

CONCLUSION

Microstructural alterations after surgery in the visuospatial network tracts may contribute to the stereopsis restoration. Additionally, the results of the correlation analysis may signify that the balanced binocular input may be more conducive for the restoration and improvement of binocular visual function, including stereopsis. Thus, restoring normal ocular balance after surgical correction may be necessary to achieve more substantial improvements.

Disrupted neural signals in patients with concomitant exotropia

PURPOSE

Decreased binocular and oculomotor function in strabismics has recently been considered as cortical in origin. This study aimed to investigate functional abnormalities using a frequency-specific neuroimaging method in patients with concomitant exotropia (XT), and to demonstrate the clinical implications.

METHODS

Resting-state functional magnetic resonance imaging data were collected in 26 XT patients and 26 matched controls. To evaluate the local spontaneous neural activity, the amplitude of low frequency fluctuations (ALFF) was calculated in the typical frequency band (0.01-0.08 Hz) as well as five narrowly-defined frequency bands (slow-6: 0-0.01 Hz, slow-5: 0.01-0.027 Hz, slow-4: 0.027-0.073 Hz, slow-3: 0.073-0.167 Hz, and slow-2: 0.167-0.25 Hz), respectively.

RESULTS

Patients with XT showed decreased ALFF in the bilateral parieto-occipital sulcus (POS), and increased ALFF in the bilateral thalamus within the typical frequency band. Frequency-dependent ALFF alterations were found in the higher visual areas such as the right lateral occipital complex (LOC). Furthermore, ALFF in the right LOC in the slow-5 band was positively correlated with fusion control score (r = 0.70, p < 0.0001) and binocular function score (r = 0.67, p = 0.0002). Regression analyses showed that early age of onset remained the only significant explanatory factor for ALFF reduction in the right POS in the typically-measured frequency band (also referred to as the typical frequency band) (Odds ratio, 0.038; 95% confidence interval, 0.001 to 0.075).

CONCLUSIONS

Our findings provide spatial information regarding the functionally disrupted regions in XT. Moreover, the frequency-dependent ALLF alteration in the right LOC might reflect a potential plastic capacity in binocular function, which could be a potential objective index for evaluating disease severity.

Quantifying Nasotemporal Asymmetry of Interocular Suppression in Alternating Strabismus After Correction

Purpose

This study identifies and characterizes the nasotemporal hemifield difference of interocular suppression in subjects who have been successfully treated for strabismus.

Methods

Interocular suppression in the nasal and temporal hemifields were measured using two methods, namely, binocular phase combination and dichoptic motion coherence, both entailed suprathreshold stimuli. We tested 29 clinical subjects, who had strabismus (19 with exotropia and 10 with esotropia) but regained good ocular alignment (within 10 prism diopters) after surgical or refractive correction, and 10 control subjects.

Results

Both the hemifield binocular phase combination and the hemifield dichoptic motion coherence tests revealed similar nasotemporal asymmetry of interocular suppression. Subjects with previous exotropia showed deeper suppression in the nasal hemifield, and those with previous esotropia showed deeper suppression in the temporal hemifield. This finding was consistent with the hemifield suppression theory. Furthermore, there was deeper suppression but less imbalance of nasotemporal asymmetry in the hemifield dichoptic motion coherence test. Finally, clinical stereopsis and the nasotemporal asymmetry of suppression (P < 0.05 in both tests) were negatively correlated in subjects with previous exotropia and measurable stereopsis.

Conclusions

Hemifield asymmetry of interocular suppression in corrected strabismus can be measured by using static and dynamic suprathreshold stimuli. Thus, the evaluation of binocular vision in strabismus should focus on both the magnitude and the pattern of interocular suppression.

Motor and Sensory Outcomes of Infantile Exotropia: A 10-Year Study (2008-2017)

Purpose

We aimed to determine the long-term motor and sensory outcomes of patients with infantile exotropia.

Methods

In this longitudinal retrospective (historical cohort) study, the records of 76 patients with infantile exotropia were Studied. Subjects with constant exotropia manifesting before the age of 1 year who were at least 5 years old at recruitment time between 2008 and 2017 were included.

Results

The medical records of 26 patients were excluded due to not participating in follow-up examinations or having incomplete records. In total, 54 infantile exotropic patients (51.9% male) with a mean age of 11.1 ± 6.8 years and follow-up of 4.99 ± 3.58 years were studied. Postoperative sensory outcomes (central stereopsis [<60 sec/arc], peripheral fusion [60–3,000 sec/arc], and non-stereopsis [>3,000 sec/arc]) were observed in 38.9%, 38.9%, and 21.2% of patients, respectively. In terms of postoperative motor outcomes, 69%, 24%, and 7% were achieved as orthophoria, residual exotropia, and consecutive esotropia, respectively. Patients with a higher surgical age (p = 0.022) and better visual acuity (p = 0.004) had significantly better sensory outcomes, while higher preoperative deviation resulted in more suppression (p = 0.039, rs = 0.218).

Conclusions

With rates of 69% for motor success and 78.8% for sensory success, surgical outcomes of infantile exotropic patients seems to be favorable. Further studies are recommended to verify our findings.

Patching and Suppression in Amblyopia: One Mechanism or Two?

Purpose

To determine if benefits from occlusion therapy are due to decreased suppression from the fellow eye in children with amblyopia.

Methods

Ten newly diagnosed amblyopes (7.2 ± 1.4 years old), two with strabismus and eight with anisometropia, participated. Patients were first given a 2-month period of refractive adaptation, followed by occlusion therapy (i.e., patching their fellow eye with an opaque patch for 4 h/day). Visual acuity of the amblyopic eye and interocular suppression were measured before and after 0.5, 1, 2, 4, and 6 months of occlusion therapy. We quantified interocular suppression with a binocular phase combination task.

Results

Visual acuity (in logMAR) improved from 0.50 ± 0.22 (mean ± SD) to 0.33 ± 0.20 for patients who finished a short-term (2 months) occlusion (A1–A10), from 0.53 ± 0.20 to 0.32 ± 0.22 for patients who finished a medium-term (4 months) occlusion (A1–A9), and from 0.48 ± 0.19 to 0.22 ± 0.10 for patients who finished a long-term (6 months) occlusion (A1–A8). Although their visual acuity significantly improved, their degree of suppression, which was abnormal in all cases, did not change consistently. This was true in all durations of occlusion therapy.

Conclusion

Reduced suppression from the fixing eye might not be result from occlusion therapy.

Health-related quality of life correlated with the clinical severity of intermittent exotropia in children

OBJECT

To evaluate whether the results of the health-related quality of life (HRQOL) is associated with the various clinical aspects of intermittent exotropia in children.

METHODS

The HRQOL of children and their parents was evaluated prospectively using the Intermittent Exotropia Questionnaire (IXTQ). The deviation angle, stereo function, sensory fusion, and strabismus control were measured.

RESULTS

Two hundred and sixty six children with intermittent exotropia (aged 5-17 years) were included in the study. Child HRQOL was significantly correlated with clinical severity; lower IXTQ scores were associated with a larger deviation (p < 0.001 both for distance and near) and poorer Newcastle control scores (p < 0.001). Proxy child HRQOL was significantly correlated with the deviation (p < 0.001), Newcastle control scores (p < 0.001) and stereo function (p < 0.05). Parent HRQOL was associated with their child's deviation (p < 0.01) and stereo function (p < 0.005). Multiple linear regression analysis suggested that the deviation angle at distance and the Newcastle control score at home were associated with the child's HRQOL.

CONCLUSION

Both the child and their parents' HRQOL showed a trend toward correlating with clinical severity. Large deviation, poor control, and poor stereo function were significantly associated with lower IXTQ scores. The deviation angle at distance and exotropia control at home were associated with the child's HRQOL.

Cortical Alterations by the Abnormal Visual Experience beyond the Critical Period: A Resting-state fMRI Study on Constant Exotropia

Purpose: The pathological mechanisms of constant exotropia (XT) are still not understood. This study aimed to critically investigate whether patients with XT express neuronal activity changes after the critical period of visual development and further explore how these alterations are associated with behavioral performance.Materials and methods: Fourteen patients with XT and 16 healthy controls (HCs) underwent resting-state functional magnetic resonance imaging (fMRI). The regional homogeneity (ReHo) method was used to evaluate spontaneous brain activities. The association between significantly altered mean ReHo values and behavioral performance was assessed using Pearson's correlation analysis.Results: Compared with HCs, the right secondary visual cortex (V2) in patients with XT exhibited increased ReHo values, whereas the left Brodmann area 47 (BA47) demonstrated decreased spontaneous ReHo values. In patients with XT, the correlation between the left BA47's mean ReHo value and duration of strabismus was positively significant.Conclusions: These findings indicate that patients with XT have severe neural dysfunction in the right V2 and left BA47, and pathological severity in the left BA47 is likely influenced by duration of ongoing strabismus. Therefore, these results may provide clinically important information toward understanding the underlying pathological mechanisms of XT and thus can be fundamental in future XT research.

The Binocular Balance at High Spatial Frequencies as Revealed by the Binocular Orientation Combination Task

How to precisely quantify the binocular eye balance (i.e., the contribution that each eye makes to the binocular percept) across a range of spatial frequencies using a binocular combination task, is an important issue in both clinical and basic research. In this study, we aimed to compare the precision of a binocular orientation combination paradigm with that of the standard binocular phase combination paradigm in measuring the binocular eye balance at low to high spatial frequencies. Nine normal adults (average age: 24.6 ± 2.0 years old) participated. Subjects viewed an LED screen dichoptically with polarized glasses in a dark room. The method of constant stimuli was used to quantitatively assess the point of subjective equality (PSE), i.e., the interocular contrast ratio when two eyes are balanced in binocular combination, for stimulus spatial frequencies from 0.5 to 8 cycles/degree. Precision was quantified by the variance [i.e., standard error (SE), obtained from 100 bootstrap estimates] associated to the PSE. Using stimuli whose interocular phase difference at the edge of the gratings was matched at 45°, we found that the orientation paradigm provides more precision than the standard binocular phase combination paradigm, especially at high frequencies (Experiment 1). Such differences remained when using stimuli that had three times larger interocular phase difference (Experiment 2) or displayed at four times higher stimuli resolution (Experiment 3). Our results indicate that a binocular combination tasked based on orientation rather than phase, provides a more precise estimate of binocular eye balance in human adults at high spatial frequencies, thus allowing a binocular balance to be assessed within the spatial region where amblyopes are most defective (i.e., high spatial frequencies).

Outcomes of undercorrection in surgical management and binocular vision gained of adult intermittent exotropia

Purpose

To study the surgical outcomes of intended undercorrection on adult intermittent exotropia (X(T)) performed to avoid postopertively overcorrected diplopia.

Patients and methods

A retrospective chart review was conducted for adult patients (age ≥18 years) with X(T) ≥15 prism diopter (PD) who underwent strabismus surgery by a single surgeon. Inclusion criteria were 1) corrected VA ≥20/40 in either eye; 2) monocular occlusion at least 30 minutes before deviation measurement; 3) difference of ≤10 PD between near and distance deviation; 4) absence of significant A or V pattern or vertical deviation; 5) lateral rectus recession and medial rectus resection procedure were performed unilaterally; and 6) intended surgical number for deviation correction was aimed at 5 PD undercorrection.

Results

Of 234 patients who met the inclusion criteria, 122 were women (52.14%). Average age at the time of surgery was 27.56 years (range, 18–42 years). A total number of 197 patients (84.19%) had postoperative exodeviation under 10 PD. Twenty five (10.68%) and 12 patients (5.13%) had postoperative exodeviation within 10–15 PD and >15 PD, respectively. All patients who had postoperative exodeviation >15 PD exhibited initial deviation of ≥40 PD and had undergone re-operation. In 74 patients (46.25%) out of 160 who had no binocular vision in orthoptic examination before surgery, fusion or stereopsis was gained after good alignment. No postoperative diplopia was found in this study.

Conclusion

Intended undercorrection in surgical management of adult X(T) showed good functional and cosmetic outcomes. No procedure resulted in consecutive esodeviation or persistent diplopia. Fusion or stereopsis could be gained after successful surgical alignment. Our recommendations are as follows: 5 PD undercorrection if deviation is <40 PD and regular correction if deviation is ≥40 PD.

On the Relationship Between Sensory Eye Dominance and Stereopsis in the Normal-Sighted Adult Population: Normative Data

The extent of sensory eye dominance, a reflection of the interocular suppression in binocular visual processing, can be quantitatively measured using the binocular phase combination task. In this study, we aimed to provide a normative dataset for sensory eye dominance using this task. Based on that, we also assessed the relationship between perceptual eye dominance and stereopsis. One-hundred and forty-two adults (average age: 24.00 ± 1.74 years old) with normal or corrected to normal monocular visual acuity (logMAR < 0.00) participated. Observer's sensory eye dominance was quantified in two complementary ways: the interocular contrast ratio when the two eyes were balanced (i.e., the balance point) and the absolute value of the binocular perceived phase when each eye viewed maximum contrast stimuli in binocular phase combination task. Stereo acuities were measured with maximum contrast stimuli using an identical spatial frequency (0.30 cycles/degree) and stimulus arrangement to that used in the eye dominance assessment. The averaged balance point was 0.93 ± 0.06 (Mean ± SD), the averaged absolute value of the binocular perceived phase when both eyes viewed maximum contrast stimuli was 7.62 ± 5.91°, and the averaged stereo acuity was 2.19 ± 0.34 log arc seconds. Neither of these two sensory eye dominance measures were significantly correlated with stereo acuity (Balance point: ρ = 0.14, P = 0.10; Phase: ρ = -0.13, P = 0.13). The sensory eye dominance, as reflected using a phase combination task, and stereopsis are not significantly correlated in the normal-sighted population at low spatial frequencies.

Role of fusional convergence amplitude in postoperative phoria maintenance in children with intermittent exotropia

PURPOSE

To examine the role of fusional convergence amplitude in postoperative phoria maintenance in childhood intermittent exotropia [X(T)].

METHODS

The medical records of 29 children aged 15 years or younger (mean age, 10.8 ± 2.4 years) and treated with monocular recession-resection for X(T) were reviewed retrospectively. The patients' fusional convergence amplitude (break point/total amplitudes), physiologic diplopia, and phoria maintenance (presence/absence of phoria maintenance and ability to maintain phoria) were assessed. The presence of phoria maintenance was confirmed by a cover test, and the ability to maintain phoria was quantified using the Bagolini red filter bar. Correlations of the amplitude size with the presence and ability of phoria maintenance were investigated.

RESULTS

A significant correlation was seen between fusional amplitude (break point/total) and ability to maintain phoria at near and at far (break point: P < .05 at near/P < .01 at far; total: P < .05 at near/far). Neither the break point amplitude nor the total amplitude significantly differed between the patients with phoria maintenance and those without it (break point: P = .71 at near, P = .29 at far; total: P = .98 at near, P = .85 at far). Phoria maintenance correlated with the suppression of physiologic diplopia during phoria (P < .01). The deviation angle did not significantly correlate with fusional amplitude either at near (P = .58) or at far (P = .27).

CONCLUSIONS

In childhood X(T), fusional amplitude plays a role in enforcing the patient's ability to maintain phoria. However, sufficient fusional amplitude does not guarantee fully functioning fusion if suppression is present during phoria.

Straightening the Eyes Doesn't Rebalance the Brain

Surgery to align the two eyes is commonly used in treating strabismus. However, the role of strabismic surgery on patients' binocular visual processing is not yet fully understood. In this study, we asked two questions: (1) Does realigning the eyes by strabismic surgery produce an immediate benefit to patients' sensory eye balance? (2) If not, is there a subsequent period of "alignment adaptation" akin to refractive adaptation where sensory benefits to binocular function accrue? Seventeen patients with strabismus (mean age: 17.06 ± 5.16 years old) participated in our experiment. All participants had normal or corrected to normal visual acuity (LogMAR < 0.10) in the two eyes. We quantitatively measured their sensory eye balance before and after surgery using a binocular phase combination paradigm. For the seven patients whose sensory eye balance was measured before surgery, we found no significant change [t₍₆₎ = -0.92; p = 0.39] in the sensory eye balance measured 0.5-1 months after the surgery, indicating that the surgical re-alignment didn't by itself produce any immediate benefit for sensory eye balance. To answer the second question, we measured 16 patients' sensory eye balance at around 5-12 months after their eyes had been surgically re-aligned and compared this with our measurements 0.5-1 months after surgery. We found no significant change [t₍₁₅₎ = -0.89; p = 0.39] in sensory eye balance 5-12 months after the surgery. These results suggest that strabismic surgery while being necessary is not itself sufficient for re-establishing balanced sensory eye dominance.

The effect of Lasik surgery on myopic anisometropes' sensory eye dominance

Lasik is a common surgery for treating anisometropia. In this study, we asked a specific question: what’s the effect of Lasik surgery on anisometropes’ sensory eye dominance? Fifteen myopic anisometropes (mean age: 23 ± 6.9 years old; 6 females) participated in our experiment. We quantitatively measured participants’ sensory eye dominance before and after the Lasik surgery using a binocular phase combination paradigm. We found no significant change of sensory eye dominance within 16 weeks (measured between 8 to 96 days, for one or two repetitions) after the surgery (t(14) = −1.44, p = 0.17). A further following on eight patients showed that patients’ two eyes were much more balanced at 16 weeks or more (measured one or two times between 112 to 408 days) after the surgery (t(7) = −3.79, p = 0.007). Our results suggest that the benefit of Lasik surgery on anisometropes’ sensory eye dominance is not immediate, a long-term ‘adaptation’ period (16 weeks or more) is necessary to enable the surgery to be truly effective.

Sensory Eye Dominance in Treated Anisometropic Amblyopia

Amblyopia results from inadequate visual experience during the critical period of visual development. Abnormal binocular interactions are believed to play a critical role in amblyopia. These binocular deficits can often be resolved, owing to the residual visual plasticity in amblyopes. In this study, we quantitatively measured the sensory eye dominance in treated anisometropic amblyopes to determine whether they had fully recovered. Fourteen treated anisometropic amblyopes with normal or corrected to normal visual acuity participated, and their sensory eye dominance was assessed by using a binocular phase combination paradigm. We found that the two eyes were unequal in binocular combination in most (11 out of 14) of our treated anisometropic amblyopes, but none of the controls. We concluded that the treated anisometropic amblyopes, even those with a normal range of visual acuity, exhibited abnormal binocular processing. Our results thus suggest that there is potential for improvement in treated anisometropic amblyopes that may further enhance their binocular visual functioning.

Microstructural changes of the whole brain in patients with comitant strabismus: evidence from a diffusion tensor imaging study

OBJECTIVE

The aim of this study was to investigate the fractional anisotropy (FA) and mean diffusivity (MD) using a diffusion tensor imaging technique and whole-brain voxel-based analysis in patients with comitant strabismus.

PATIENTS AND METHODS

A total of 19 (nine males and ten females) patients with comitant strabismus and 19 age-, sex-, and education-matched healthy controls (HCs) underwent magnetic resonance imaging examination. Imaging data were analyzed using two-sample t-tests to identify group differences in FA and MD values. Patients with comitant strabismus were distinguishable from HCs by receiver operating characteristic curves.

RESULTS

Compared with HCs, patients with comitant strabismus exhibited significantly decreased FA values in the brain regions of the left superior temporal gyrus and increased values in the bilateral medial frontal gyrus, right globus pallidus/brainstem, and bilateral precuneus. Meanwhile, MD value was significantly reduced in the brain regions of the bilateral cerebellum posterior lobe and left middle frontal gyrus but increased in the brain regions of the right middle frontal gyrus and left anterior cingulate.

CONCLUSION

These results suggest significant brain abnormalities in comitant strabismus, which may underlie the pathologic mechanisms of fusion defects and ocular motility disorders in patients with comitant strabismus.