Benefit of bi-ocular visual stimulation for postural control in children with strabismus

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).

Sufficiency of the BOT-2 short form to screen motor competency in preschool children with strabismus

Background

Strabismus is one of the most common visual disorders in children, with a reported prevalence of 2.48% in preschoolers. Additionally, up to 89.9% of preschool children with strabismus do not have normal stereopsis. Whether this lack of normal stereopsis affects the motor competency of preschool children with strabismus is unknown. The Bruininks-Oseretsky Test of Motor Proficiency Second Edition short form (BOT-2 SF) can be a useful tool for screening; however, its sufficiency as a diagnostic tool for children with various disorders is controversial.

Objective

The aims of this study were thus to examine motor competency in preschool children with strabismus by using the BOT-2 and to evaluate the usefulness of the BOT-2 SF to identify those at risk for motor competency issues.

Methods

Forty preschool children (aged 5–7 years) with strabismus were recruited, all of whom had abnormal stereopsis. The BOT-2 complete form (CF) was administered to all children. The BOT-2 CF was administered to all children. The scores of the BOT-2 SF were extracted from the relevant items of the BOT-2 CF for further analysis.

Results

The prevalence of children with strabismus who had below average performance in the composites of “Fine Manual Control”, “Manual Coordination”,”Body Coordination”, and “Strength and Agility” were 15%, 70%, 32.5%, and 5%, respectively, on the BOT-2 CF. Compared with these results, the sensitivity of the BOT-2 SF was 33.33% (95% CI = 7.49%–70.07%) and the specificity was 100% (95% CI = 88.78%–100%).

Conclusion

Preschool children with strabismus had a high prevalence of impaired motor competency, especially in fine motor competency. The BOT-2 SF was not as sensitive in identifying motor difficulties in preschool children with strabismus. Therefore, the BOT-2 CF is recommended for evaluating motor proficiency in preschool children with strabismus.

Motor Competence in Children With and Without Ambliopia

The purpose of this study was to assess the motor competence of children with and without amblyopia. Study participants were 165 primary school children, aged 6-9 years, divided into three groups based on their visual acuity with the Snellen chart: (a) non-amblyopia, (b) corrected amblyopia, and (c) non-corrected amblyopia. We assessed the children's motor competence with the Motor Competence Assessment battery (MCA) and their physical activity with the Physical Activity Questionnaire for Older Children (PAQ-C). The non-amblyopia group presented significantly better motor competence on the MCA than either the corrected amblyopia group or the non-corrected amblyopia group; there were no statistically significant motor differences between the two amblyopia subgroups. Amblyopia versus non-amblyopia differences on the MCA were mainly in stability and locomotor components, involving dynamic balance and the change of spatial position and direction of movement, but not in the manipulative component (ball throwing velocity and ball kicking velocity). Predictably, from within an integrated visual motor perspective of child development, our findings suggest that intact vision played an important role in children's motor competence. The development of fundamental motor skills, especially of stability and locomotor skills, may be affected by poor visual processing in that participants with uncorrected amblyopia showed poor movement accuracy, uncoordinated movement, and impaired balance.

Comparison of postural control between strabismic and non-strabismic children

OBJECTIVE

To compare the postural control of children with strabismus versus non-strabismus children.

MATERIAL AND METHODS

Cross-sectional cohort study with a total of 171 children, including 73 children with esotropia, 24 with exotropia, and 74 controls. Postural control was determined using a dynamometric platform in a standing position in various conditions: eyes open and eyes closed, near and gaze fixation, and with and without foam pad. The studied variables were the area, the mean speed, and the lengths in the X and Y axis of the centre of pressure displacement.

RESULTS

Children with esotropia and exotropia had significantly higher mean values (speed, lengths of X and Y) compared to controls. In the open-eye, far distance fixation, and on foam pad, as well as under exam conditions; with eyes open, without foam pad, and far distance fixation, the exotropia values were higher than those of endotropia and controls. With eyes closed, there were no differences between the 3 groups under the described examination conditions, but their values were worse compared to their respective ones with eyes open.

CONCLUSIONS

The children with strabismus had a worse postural control than the non-strabismus ones. All of the them appeared to be more unstable with eyes closed than with eyes open, which demonstrates that vision plays an important relevant role in postural stability in both strabismus and non-strabismus children.

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.

Reeducation of vergence dynamics improves postural control

INTRODUCTION

The purpose was to investigate the effect of vergence reeducation on postural control, in subjects with isolated vergence disorders.

MATERIAL AND METHODS

We studied the dynamics of vergence in 19 subjects (20-44 years old) using video-oculography (Eye See Cam). On the basis of orthoptic and symptomatology assessments, ten of the subjects were diagnosed for vergence disorders then vergence eye movements were reeducated with the REMOBI method (US8851669, 5 weekly sessions lasting for 35min). Postural control was measured before and after reeducation, postural recording was done in upright stance (Dynaport), with both eyes closed or open and looking a visual target located at 2m distance.

RESULTS

After reeducation with REMOBI, the visual symptomatology faded away and the stereoacuity improved at least for some subjects; the vergence latency decreased significantly and the vergence accuracy increased significantly. In terms of posture, the Mean Power Frequency (MPF) of the body sway decreased significantly in both eyes open and eyes closed conditions. Considering all subjects together (i.e. healthy subjects and subjects with vergence disorders before the reeducation), the antero-posterior body sway (Root Mean Square A/P) was positively correlated with the visual symptomatology: the higher the visual symptomatology, the higher was the body sway.

CONCLUSION

The results bring evidence for synergy between the quality of vergence and the quality of postural control. They open a new research line that bridges the gap between neuroscience, ophthalmology-orthoptics and posturology.

Deficits in vision and visual attention associated with motor performance of very preterm/very low birth weight children

AIM

To extend understanding of impaired motor functioning of very preterm (VP)/very low birth weight (VLBW) children by investigating its relationship with visual attention, visual and visual-motor functioning.

METHODS

Motor functioning (Movement Assessment Battery for Children, MABC-2; Manual Dexterity, Aiming & Catching, and Balance component), as well as visual attention (attention network and visual search tests), vision (oculomotor, visual sensory and perceptive functioning), visual-motor integration (Beery Visual Motor Integration), and neurological status (Touwen examination) were comprehensively assessed in a sample of 106 5.5-year-old VP/VLBW children. Stepwise linear regression analyses were conducted to investigate multivariate associations between deficits in visual attention, oculomotor, visual sensory, perceptive and visual-motor integration functioning, abnormal neurological status, neonatal risk factors, and MABC-2 scores.

RESULTS

Abnormal MABC-2 Total or component scores occurred in 23-36% of VP/VLBW children. Visual and visual-motor functioning accounted for 9-11% of variance in MABC-2 Total, Manual Dexterity and Balance scores. Visual perceptive deficits only were associated with Aiming & Catching. Abnormal neurological status accounted for an additional 19-30% of variance in MABC-2 Total, Manual Dexterity and Balance scores, and 5% of variance in Aiming & Catching, and neonatal risk factors for 3-6% of variance in MABC-2 Total, Manual Dexterity and Balance scores.

CONCLUSION

Motor functioning is weakly associated with visual and visual-motor integration deficits and moderately associated with abnormal neurological status, indicating that motor performance reflects long term vulnerability following very preterm birth, and that visual deficits are of minor importance in understanding motor functioning of VP/VLBW children.

Walking strategies in subjects with congenital or early onset strabismus

Introduction: In congenital strabismus, sensory adaptations occur hampering the correct development of normal binocular vision. The aim of this study is to investigate if patients with congenital or early onset exotropic or esotropic strabismus adopt different walking strategies with respect to healthy subjects. Our hypothesis is that the abnormal binocular cooperation, occurring in patients with exotropic or esotropic strabismus, could influence neurosensorial adaptation of the gait pattern.

Materials and Methods: Twenty-five patients were enrolled: 19 with esotropic (ESO) and 6 with exotropic strabismus (EXO). All patients underwent an ophthalmological and orthoptic evaluation. Biomechanical data were collected using a stereophotogrammetric system and a force platform. Twenty-seven age-matched healthy subjects (HS) were used as controls.

Results: The comparison between patients with ESO and patients with EXO strabismus showed that the maximal power at the knee and at the ankle was lower in EXO group (p < 0.01 and p < 0.05, respectively). The step width was statistically different between ESO and EXO groups (p < 0.01), lower in patients with ESO and higher in patients with EXO strabismus when compared with HS (though not statistically significant). The deviation angle values showed a relationship with the step width (at the near fixation p < 0.05) and with the maximal power at the knee and at the ankle (at the far fixation for the knee p < 0.001 and for the ankle p < 0.05; at the near fixation for the knee p < 0.05): in the patients with EXO the increased angle deviation is related to larger step width and to lower power at the knee and at the ankle. In the patients with ESO strabismus this relationship is less robust.

Discussion: Patients with EXO and ESO strabismus adopt different strategies to compensate their walking difficulties, and these strategies are likely due to an expanded binocular visual field in patients with EXO and to a reduced visual field in patients with ESO strabismus.

Impaired body balance control in adults with strabismus

Previous studies revealed that people with binocular vision disorders have poor postural stability. However, most of the research was performed only on children and under binocular viewing condition, that could negatively affect the results. The aim of the current study was to investigate the influence of extra-ocular proprioceptive signals on postural stability in young adults with binocular vision disorders. Moreover, additional mental task was introduced to detect any postural compensation which could possibly hide the real influence of afferent extra-ocular signals. 21 Subjects, aged 18-45 yrs, with horizontal strabismus, were qualified to binocular vision disorders (BVD) group. 41 subjects, aged 19-45 yrs, with no strabismus formed the normal binocular vision (NBV) group. Posturography data were collected in 2 separate parts: (1) quiet standing (Single-Task), and (2) performance of a mental task while standing (Dual-Task). Each part consisted of three 60-s viewing conditions, with: (1) dominant/fellow eye (DE), (2) non-dominant/strabismic eye (NDE), and with (3) both eyes closed (EC). Subjects were looking at X located at the distance of 150 cm. Generally, BVD group showed elevated body balance during quiet stance compared to NBV group. Interestingly, better stabilization in BVD group occurred under NDE viewing. Surprisingly, additional mental task improved the postural stability in BVD group almost to the level of NBV group. These findings emphasize the role of the eye-muscle signals in postural control and suggest that suitable vision therapy can be the appropriate way to improve body balance/motor functions in people with binocular vision disorders.