Re-alignment of the eyes, with prisms and with eye surgery, affects postural stability differently in children with strabismus

The effect of strabismus surgery on the dynamic balance in children with strabismus

Purpose: To evaluate the effect of strabismus surgery on dynamic balance by using computerized dynamic posturography in children with strabismus. Methods: This study was designed as a prospective observational study. Hearing tests and complete ophthalmological examinations were performed for all subjects. Patients with moderate and severe amblyopia, hearing loss at any level, and/or any suspicion of balance impairment were excluded from the study. Postural stability evaluation was performed by computerized dynamic posturography including sensory organization test, adaptation test, and rhythmic weight shift test. All tests were applied preoperatively and in the postoperative 1st and 3rd months, respectively. Results: Fifteen female and twelve male pre-adolescents aged between 7 and 12 (9.67 ± 1.62 years) were included in the current study. In the sensory organization test, the preoperative visual ratio percentages (73.19 ± 14.95%) improved statistically significantly at the postoperative 1st and 3rd months (78.59 ± 16.21% and 81.44 ± 14.18; p = .026, p = .021, respectively). The preoperative toes up (110.66 ± 33,48) and toes down (81.46 ± 28.36) adaptation tests improved statistically significantly in the postoperative 3rd month (88.74 ± 20.94 and 63.36 ± 16.03; p < .001, p = .001, respectively). In the Rhythmic Weight Shift test, the postoperative 3rd-month directional control (forward-backward) value (74.25 ± 11.51%) was statistically significantly higher compared to the preoperative directional control (forward-backward) value (67.76 ± 11.38%) (p = .011). The postoperative 3rd-month directional control (forward-backward) value (74.25 ± 11.51%) was statistically significantly higher compared to the postoperative 1st-month directional control (forward-backward) value (68.43 ± 14.00%) (p = .028). Conclusion: Surgical treatment resulted in an improvement in the maintenance of dynamic balance in children with strabismus.

Postural stability in strabismus and amblyopia

BACKGROUND

Postural control is a complex skill based on the collaboration of dynamic sensory mechanisms, namely the visual, vestibular, and somatosensory systems.

METHODS

A literature survey regarding postural stability in strabismus and amblyopia was conducted using databases in order to collect data for a narrative review of published reports and available literature.

RESULTS

The results of the literature survey were analyzed to provide an overview of the current knowledge of postural stability in strabismus and amblyopia. The results revealed that although postural control depends on the fundamental integration of three essential components (the visual, vestibular, and somatosensory systems), the role of vision is critical in postural stability. Once normal binocular vision is undesirably disrupted in childhood by some reason, especially in strabismus and/or amblyopia, balance is also affected. Abnormal balance affects coordination in gross and fine motor controls in school-age children and results in weakened academic performance and delayed social progress. It also impacts a child's general health, self-esteem, and safety.

CONCLUSIONS

Binocular vision is imperative for the maturation and preservation of balance control in children, as balance performance is reduced in strabismus and/or amblyopia.

Amblyopia and the whole child

Amblyopia is a disorder of neurodevelopment that occurs when there is discordant binocular visual experience during the first years of life. While treatments are effective in improving visual acuity, there are significant individual differences in response to treatment that cannot be attributed solely to difference in adherence. In this considerable variability in response to treatment, we argue that treatment outcomes might be optimized by utilizing deep phenotyping of amblyopic deficits to guide alternative treatment choices. In addition, an understanding of the broader knock-on effects of amblyopia on developing visually-guided skills, self-perception, and quality of life will facilitate a whole person healthcare approach to amblyopia.

Strabismus Surgery Decreases the Risk of Injuries in Pediatric Patients in the OptumLabs Data Warehouse

PURPOSE

Previous studies have shown an association between injury risk and strabismus in aged Medicare beneficiaries and children. The injury prevalence in strabismic children was 30% in a study of >10 million patients in the OptumLabs Data Warehouse. The purpose of this study was to determine whether strabismus surgery decreases the risk of injury.

DESIGN

Retrospective cohort study.

METHODS

The OptumLabs Data Warehouse is a deidentified, longitudinal health database that was queried for strabismic patients aged <19 years. The patients who underwent strabismus surgery were compared with those strabismic patients who did not undergo surgery for injury. Injury risk (fractures, musculoskeletal injuries, and head injuries) during their insurance enrollment was calculated in the nonsurgical patients after their first strabismus claim and compared with the risk in surgical patients postoperatively.

RESULTS

There were 344,794 patients with strabismus. Surgery was performed in 26,459 (7.7%). Esotropia was the most common diagnosis (n = 181,195, 52.6%) followed by exotropia (n = 161,712, 46.9%) and hypertropia (n = 43,831, 12.7%). Within these groups, patients with hypertropia were significantly more likely to undergo surgery (24.2%) compared with patients with esotropia and exotropia (10.2% and 9.6%, respectively). Injuries were diagnosed after the first strabismus claim in 94,960 (29.8%) nonsurgical patients vs 5790 (21.9%) postsurgical patients (P < .001) with a mean follow-up of 4.3 ± 3.1 vs 3.8 ± 3.1 years, respectively. The adjusted hazard ratio for injuries was 0.85 (95% confidence interval [CI]: 0.83-0.87) for the risk of any injury after strabismus surgery. The hazard ratio was significantly decreased after surgery for each type of strabismus: esotropia (0.91, 95% CI: 0.88-0.94), exotropia (0.82, 95% CI: 0.80-0.85), and hypertropia (0.89, 95% CI: 0.85-0.93).

DISCUSSION

Strabismus surgery was associated with a 15% decrease in the risk of physical injury over approximately 4 years of follow-up. Surgery may be a factor in decreasing injury risk in strabismic patients, particularly in exotropia. Given the large number of children with strabismus in the United States, further assessment of strategies such as strabismus surgery to reduce injuries in children with strabismus is needed.

Strabismus and postural control: a systematic review

The primary aim of this systematic review is to evaluate how postural balance and visual system are related in cross-eyed patients. The secondary goal is to assess the benefits of eye realignment on motor skills and body balance. Analyzing two different approaches: surgical or conservative, a systematic literature search was conducted using PubMed-Medline, Google Scholar and Cochrane Central in order to identify randomized controlled trials, case series and case-control studies which contained clinical evaluation of balance in strabismic patients as well as re-evaluation after surgery or conservative treatments via posturography to evaluate surface, length and mean speed of the center of pressure (CoP). A total of 11 studies were included in this review. The MINORS score is used to assess the methodological quality of the included studies, and its mean value was 12.8 for non-comparative studies and 17.5 for comparative studies. The postural balance was lower in strabismic patients compared with the control group, with statically higher value (p < 0.05) of surface, length and mean speed of the CoP in the study group. All patients show improvement in stability after surgery, as surface, length and mean speed of the CoP decreased after surgery in all the studies with statistical significance (p < 0.05).

Sensory organization for postural control in children with strabismus-A systematic review and meta-analysis

BACKGROUND

Postural control requires the interaction of somatosensory, vestibular and visual systems to prevent disequilibrium. Children with strabismus have an impaired visual input which can lead to postural control deficits.

RESEARCH QUESTION

Does strabismus affect sensory organization for postural control in children?

METHODS

A systematic comprehensive search of multiple electronic databases for relevant articles was performed using a predetermined search strategy. Peer-reviewed journal publications that assessed sensory organization and postural performance in children with strabismus were included in this review. Methodological quality of the articles was evaluated using the modified Downs and Black quality assessment tool. A total of 10 articles were included in this review.

RESULTS

Eight of the 10 articles reviewed were included in the meta-analysis. Meta-analysis for Centre of Pressure CoP velocity (n = 3) (eyes open, stable support), was statistically significant (P = 0.01) in favor of controls over children with strabismus (MD, 3.08; 95 % CI -0.66, 5.51). Meta-analysis for CoP surface area (n = 5) (eyes open, stable support) was also statistically significant (P < 0.001) in favor of the control group (MD, 130.14; 95 % CI 70.01, 190.260). Meta-analysis with standardized mean difference (n = 6) for eyes open vs closed, stable support was statistically significant (P = 0.02) in favor of eyes open (MD, -0.94; 95 % CI, -1.74, -0.15). Overall, there was a high level of heterogeneity throughout the studies.

SIGNIFICANCE

This is the first systematic review of its kind to collate and synthesize evidence on the effect of strabismus on postural control in children. This review suggests that postural control performance in children with strabismus is inferior to that of age-matched control children. Further investigation is needed to understand the influence of the three sensory systems.

A dichoptic feedback-based oculomotor training method to manipulate interocular alignment

Strabismus is a prevalent impairment of binocular alignment that is associated with a spectrum of perceptual deficits and social disadvantages. Current treatments for strabismus involve ocular alignment through surgical or optical methods and may include vision therapy exercises. In the present study, we explore the potential of real-time dichoptic visual feedback that may be used to quantify and manipulate interocular alignment. A gaze-contingent ring was presented independently to each eye of 11 normally-sighted observers as they fixated a target dot presented only to their dominant eye. Their task was to center the rings within 2° of the target for at least 1 s, with feedback provided by the sizes of the rings. By offsetting the ring in the non-dominant eye temporally or nasally, this task required convergence or divergence, respectively, of the non-dominant eye. Eight of 11 observers attained 5° asymmetric convergence and 3 of 11 attained 3° asymmetric divergence. The results suggest that real-time gaze-contingent feedback may be used to quantify and transiently simulate strabismus and holds promise as a method to augment existing therapies for oculomotor alignment disorders.

Visual Binocular Disorders and Their Relationship with Baropodometric Parameters: A Cross-Association Study

The aim of this study was to establish a relationship between nonstrabismic binocular dysfunction and baropodometric parameters. A total of 106 participants underwent binocular vision assessment by evaluating horizontal heterophoria, horizontal and vertical fusional vergence ranges, and vergence facility. Posturography was measured using the FreeMED baropodometric platform. Among the variables that the software calculates are foot surface, foot load, and foot pressure. Our results showed that in the participants with positive fusional vergence (PFV) (near) blur and recovery values outside the norm, there are statistically significant differences between the total foot area (p < 0.05), forefoot area (p < 0.05), forefoot load (p < 0.05), and rearfoot load (p < 0.05), in all of the cases of left foot vs. right foot. In the group of subjects who did not meet Sheard's criterion (distance), that is, those with unstable binocular vision, there was a statistically significant difference (p < 0.01) between maximum left and right foot pressure. In conclusion, our results establish a relationship between nonstrabismic binocular dysfunctions and some baropodometric parameters.

Transfer and retention of oculomotor alignment rehabilitation training

Ocular alignment defects such as strabismus affect around 5% of people and are associated with binocular vision impairments. Current nonsurgical treatments are controversial and have high levels of recidivism. In this study, we developed a rehabilitation method for ocular alignment training and examined the rate of learning, transfer to untrained alignments, and retention over time. Ocular alignment was controlled with a real-time dichoptic feedback paradigm where a static fixation target and white gaze-contingent ring were presented to the dominant eye and a black gaze-contingent ring with no fixation target was presented to the nondominant eye. Observers were required to move their eyes to center the rings on the target, with real-time feedback provided by the size of the rings. Offsetting the ring of the nondominant temporal or nasal visual field required convergent or divergent ocular deviation, respectively, to center the ring on the fixation target. Learning was quantified as the time taken to achieve target deviation of 2° (easy, E) or 4° (hard, H) for convergence (CE, CH) or divergence (DE, DH) over 40 trials. Thirty-two normally sighted observers completed two training sequences separated by one week. Subjects were randomly assigned to a training sequence: CE-CH-DE, CH-CE-DE, DE-DH-CE, or DH-DE-CE. The results showed that training was retained over the course of approximately one week across all conditions. Training on an easy deviation angle transferred to untrained hard angles within convergence or divergence but not between these directions. We conclude that oculomotor alignment can be rapidly trained, retained, and transferred with a feedback-based dichoptic paradigm. Feedback-based oculomotor training may therefore provide a noninvasive method for the rehabilitation of ocular alignment defects.

The Role of Binocular Vision in Driving Pseudoneglect in Visual and Haptic Bisection: Evidence From Strabismic and Monocular Blind Individuals

Prior studies have shown that strabismic amblyopes do not exhibit pseudoneglect in visual line bisection, suggesting that the right-hemisphere dominance in the control of spatial attention may depend on a normally developing binocular vision. In this study, we aimed to investigate whether an abnormal binocular childhood experience also affects spatial attention in the haptic modality, thus reflecting a supramodal effect. To this aim, we compared the performance of normally sighted, strabismic and early monocular blind participants in a visual and a haptic line bisection task. In visual line bisection, strabismic individuals tended to err to the right of the veridical midpoint, in contrast with normally sighted participants who showed pseudoneglect. Monocular blind participants exhibited high variability in their visual performance, with a tendency to bisect toward the direction of the functioning eye. In turn, in haptic bisection, all participants consistently erred towards the left of the veridical midpoint. Taken together, our findings support the view that pseudoneglect in the visual and haptic modality relies on different functional and neural mechanisms.

Postural stability and visual impairment: Assessing balance in children with strabismus and amblyopia

Background

Vision plays an important role in controlling posture and balance in children. Reduced postural control has been reported in children with strabismus, but little has been reported specifically in amblyopia.

Objective

To investigate whether children with amblyopia have reduced balance compared to both children with strabismus without amblyopia and healthy controls.

Study design and methods

In this cross-sectional study, a total of 56 patients and healthy controls were recruited from the Ophthalmology and Otolaryngology Clinics at The Hospital for Sick Children, Toronto. Participants were divided into three groups: (1) 18 with unilateral amblyopia (strabismic amblyopia or mixed mechanism); (2) 16 with strabismus only without amblyopia; and (3) 22 visually-normal controls. The primary outcome was the balance performance as measured by the balance subtest of the Bruininks-Oseretsky Test of Motor Proficiency 2 [BOT2].

Results

The age and gender-adjusted BOT2 balance scores were significantly reduced in the amblyopia group (mean score 9.0 ± 3.1 SD) and the strabismus without amblyopia group (mean score 8.6 ± 2.4 SD) compared to visually normal controls (mean score 18.9 ± 4.2) (p<0.0001), but no statistical difference was demonstrated between the two patient groups (p = 0.907). Further subgroup analysis of the strabismus only group did not reveal a statistically significant difference in performance on BOT2 balance score between strabismus only patients with good stereopsis 60 sec or better (BOT2 mean score 9.8±3.0 SD) to patients with 3000 sec or no stereopsis (BOT2 mean score 7.9±1.7) (p = 0.144).

Conclusion

Our findings suggest that normal vision plays an important role in the development and maintenance of balance control. When normal binocular vision is disrupted in childhood in strabismus and/or amblyopia, not only is the vision affected, but balance is also reduced. Our results indicate that the presence of even mild binocular discordance/dysfunction (patients with intermittent strabismus and good stereopsis) may lead to postural instability.

Beyond Rehabilitation of Acuity, Ocular Alignment, and Binocularity in Infantile Strabismus

Infantile strabismus impairs the perception of all attributes of the visual scene. High spatial frequency components are no longer visible, leading to amblyopia. Binocularity is altered, leading to the loss of stereopsis. Spatial perception is impaired as well as detection of vertical orientation, the fastest movements, directions of movement, the highest contrasts and colors. Infantile strabismus also affects other vision-dependent processes such as control of postural stability. But presently, rehabilitative therapies for infantile strabismus by ophthalmologists, orthoptists and optometrists are restricted to preventing or curing amblyopia of the deviated eye, aligning the eyes and, whenever possible, preserving or restoring binocular vision during the critical period of development, i.e., before ~10 years of age. All the other impairments are thus ignored; whether they may recover after strabismus treatment even remains unknown. We argue here that medical and paramedical professionals may extend their present treatments of the perceptual losses associated with infantile strabismus. This hypothesis is based on findings from fundamental research on visual system organization of higher mammals in particular at the cortical level. In strabismic subjects (as in normal-seeing ones), information about all of the visual attributes converge, interact and are thus inter-dependent at multiple levels of encoding ranging from the single neuron to neuronal assemblies in visual cortex. Thus if the perception of one attribute is restored this may help to rehabilitate the perception of other attributes. Concomitantly, vision-dependent processes may also improve. This could occur spontaneously, but still should be assessed and validated. If not, medical and paramedical staff, in collaboration with neuroscientists, will have to break new ground in the field of therapies to help reorganize brain circuitry and promote more comprehensive functional recovery. Findings from fundamental research studies in both young and adult patients already support our hypothesis and are reviewed here. For example, presenting different contrasts to each eye of a strabismic patient during training sessions facilitates recovery of acuity in the amblyopic eye as well as of 3D perception. Recent data also demonstrate that visual recoveries in strabismic subjects improve postural stability. These findings form the basis for a roadmap for future research and clinical development to extend presently applied rehabilitative therapies for infantile strabismus.

Visual and vestibular functioning, and age and surgery effects on postural control in healthy children with vertical strabismus

Purpose:

To describe visual and vestibular functioning and the effects of age and surgery effects on postural control in healthy children with vertical strabismus.

Design:

This is a comparative case series.

Methods:

We evaluated participants at the Scientific Institute Eugenio Medea during routine clinical activities. We enrolled 30 consecutive children/adolescents (age range 4–13 years) with isolated vertical strabismus, with and without corrective surgery. Participants were split into four subgroups according to age (4–8 years versus 9–13 years) and ocular surgery (surgery versus no surgery). The clinical protocol included ophthalmological, orthoptic, neurological, physiatrical, otolaryngological, and vestibular evaluations, and the instrumental protocol included ocular cyclotorsions assessment, posturography, and vestibular myogenic-evoked potentials. Main outcome measures of the study were the prevalence of study-relevant orthopedic, ocular, vestibular, and posturographic abnormalities.

Results:

Among the overall largely variable findings across patients’ groups, we found some interesting trends: larger binocular vision and convergence disorders in younger children, smaller prevalence of asymmetric vestibular-evoked potentials in operated children, less posturographic abnormalities in younger children. No clear-cut beneficial effect of surgery was found on all clinical and instrumental parameters considered, despite good re-alignment of the eyes.

Conclusion:

The pathophysiology of postural control in vertical strabismus is extremely complex and above the potential of this study design and should be specifically addressed in deeper experimental studies.

Importance of visual inputs quality for postural stability in strabismic children

OBJECTIVE

The first goal of the present study is to analyze the postural control in strabismic children in four different visual conditions (eyes open, eyes closed and monocular viewing with squint eye and non-squint eye). Secondly, we wish to explore the effect of strabismus surgery in postural control.

METHOD

Postural stability was recorded with a platform (TechnoConcept) in 23 strabismic children aged from 4.4 to 14.8 years old (mean age: 8.4 years); 12 of these children were also examined at least two months after strabismus surgery. We analyzed the surface, the length, and the mean speed of the Center of Pressure displacement (CdP), and we calculated the Romberg's Quotient (that is for each postural parameter the ratio between eyes closed relative to eyes open).

RESULTS

Strabismic children are significantly more stable when they can use their visual information to control their posture. Also, postural stability was better when the non-squint eye was viewing. For the first time, we observed the important role of vision (by calculating Romberg's Quotient) in strabismic children with binocular vision in comparison of strabismic children without binocular vision. Finally, we found that eye surgery improves postural stability.

CONCLUSION

Strabismic children use visual inputs to control their posture. Moreover, binocular vision plays an important role in postural control. Strabismus surgery improves postural stability.

SIGNIFICANCE

Visual inputs from the non-squint eye and binocular vision are important to control stability.

One Year of Pediatric Ophthalmology and Strabismus Research in Review

PURPOSE

To highlight recent advances in amblyopia and strabismus.

DESIGN

Literature review.

METHODS

A literature search of articles published in the English language was performed in PubMed or MEDLINE between May 2012 and April 2013 using the terms amblyopia or strabismus. Articles deemed relevant were selected.

RESULTS

The review highlights articles that increase our understanding of strabismus and amblyopia as well as newer treatment strategies.

CONCLUSIONS

The review highlights some new information and possible future advances in amblyopia and strabismus.