Peripheral sensory information and postural control in children with strabismus

Effects on Posture of a Two-Diopter Horizontal Prism Base Out on the Non-Dominant Eye

Background/Objectives: Ocular proprioception is implicated in balance control and heterophoria is associated with abnormal posture, though previous research focused mainly on the role of vertical phoria and the use of vertical prisms. This study aims to evaluate whether ocular misalignment and prismatic correction of horizontal phoria affect posture. Methods: Sixty-nine (N = 69) young healthy subjects were included and equally divided by horizontal distance phoria: orthophoria (n = 23), esophoria (n = 23) and exophoria (n = 23). A prism of low power (two-diopter) was placed base out on the non-dominant eye, reducing misalignment in esophorics and increasing it in exophorics more than in orthophorics. Dynamic computerized posturography was performed with the sensory organization test protocol (SOT) of the EquiTest® NeuroCom® version 8 platform both without and with prism, always maintaining subjects unaware of prism use. A mixed model for repeated measures analysis of variance was run to evaluate the main effect of prism and the interaction effect of prism with baseline phoria. Results: Composite movement strategy score without prism was 88.1 ± 2.8% (ankle-dominant strategy) and slightly increased to 89.0 ± 3.1% with prism insertion (p = 0.004), further shifting toward ankle strategy. Composite equilibrium score without prism was 80.3 ± 6.5% and remained stable with prism insertion (81.3 ± 8.2%, p = 0.117), medio-lateral and antero-posterior projection of center of gravity did not displace significantly under prism insertion (p = 0.652 and p = 0.270, respectively). At baseline, posturographic parameters were statistically independent of individual phoria, and no significant interaction between prism insertion and individual phoria was documented for any parameters (p > 0.05 for all). Secondary analysis and pairwise comparisons confirmed that the effect of prism was strongly selective on condition SOT 5 (eyes-closed, platform sway-referenced) with improvement of equilibrium (70.4 ± 9.7% with prism vs. 65.7 ± 11.6% without) and more use of ankle strategy (81.6 ± 5.3% with prism vs. 78.2 ± 6.0% without), without any interaction of phoria and ocular dominance, while the other conditions were comparable with and without prism. Conclusions: A two-diopter prism base out on the non-dominant eye induces the body to use the ankle joint more independently of individual phoria, suggesting a small improvement in postural control, while maintaining oscillations of the center of gravity unaltered. Prism seems to enhance the function of vestibular system selectively. Phoria adjustments with prismatic correction enable intervention in postural behavior. Extraocular muscles could act as proprioceptors influencing postural stability.

Checks and balances: a meta-analysis on the known-groups validity of functional postural control tests in children

INTRODUCTION

Pediatric physical therapists commonly treat children with postural control deficits. Ideally, pediatric functional postural control tests should therefore be able to identify postural control deficits in children with various disorders. Despite a plethora of available tests, evidence for their validity - especially known-groups - remains scarce. This review aims to determine the known-group validity of available functional postural control tests to differentiate various pediatric pathological groups of different ages from their typically developing (TD) peers.

EVIDENCE ACQUISITION

PubMed, Web of Science and Scopus were systematically searched (last update: February 2023; PROSPERO: CRD42023408982). Forty case-control studies with a pathological pediatric sample (N.=1331) and TD peers (N.=1889) were included and selected for data-extraction and -analysis. Risk of bias was assessed using the SIGN checklist and level of evidence was scored using GRADE. Random-effect meta-analyses were performed to estimate pooled standardized mean differences (SMD) for the various test types and subclassified based on pathology and/or age.

EVIDENCE SYNTHESIS

When compared with TD peers, children with underlying pathologies performed significantly worse on pediatric functional postural control test batteries (SMD=-2.21), the Timed Up and Go Test and variants (SMD=2.30), the One Leg Stance test and variants (SMD=-2.14), while the Reach tests showed a smaller difference (SMD=-1.19). Subclassification within the meta-analyses showed that pathology was an influencing factor for the test batteries and the one leg stance test and variants. Age was an influencing factor for the reach tests. None of the included functional postural control tests exceeded a low level of evidence.

CONCLUSIONS

Pediatric functional postural control tests that assess multiple aspects of postural control (such as test batteries) seem to offer higher known-groups validity than single-task tests (e.g. reach tests). The underlying pathology has a larger impact on the validity of these tests than age. There remains an overall low level of evidence for the known-groups validity of pediatric functional postural control tests indicating the need for research with more homogenous groups and norm reference data.

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).

Cortical Visual Impairments and Learning Disabilities

Medical advances in neonatology have improved the survival rate of premature infants, as well as children who are born under difficult neurological conditions. As a result, the prevalence of cerebral dysfunctions, whether minimal or more severe, is increasing in all industrialized countries and in some developing nations. Whereas in the past, ophthalmological diseases were considered principally responsible for severe visual impairment, today, all recent epidemiological studies show that the primary cause of blindness and severe visual impairment in children in industrialized countries is now neurological, with lesions acquired around the time of birth currently comprising the commonest contributor. The resulting cortical or cerebral visual impairments (CVIs) have long been ignored, or have been confused either with other ophthalmological disorders causing low vision, or with a range of learning disabilities. We present here the deleterious consequences that CVI can have upon learning and social interaction, and how these can be given behavioral labels without the underlying visual causes being considered. We discuss the need to train and inform clinicians in the identification and diagnosis of CVI, and how to distinguish the diagnosis of CVI from amongst other visual disorders, including the specific learning disorders. This is important because the range of approaches needed to enhance the development of children with CVI is specific to each child's unique visual needs, making incorrect labeling or diagnosis potentially detrimental to affected children because these needs are not met.

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.

Analysis of the potential impact of strabismus with and without amblyopia on visual-perceptual and visual-motor skills evaluated using TVPS-3 and VMI-6 tests

PURPOSE

To investigate the potential impact of strabismus and amblyopia on visual-perceptual skills (VPS) and visual-motor skills (VMS) of patients according to the type of strabismus, visual acuity (VA), state of binocularity, and sex.

METHODS

This observational, transverse, prospective study analyzed a sample of 146 children with strabismus (88 male and 58 female) aged 5-15 years from Querétaro, México. To determine the strabismus type, we considered the deviation direction, frequency, binocularity state, and associated and dissociated elements. VPS and VMS were evaluated using the Test of Visual-Perceptual Skills 3rd ed. (TVPS-3) and Visual-Motor Integration Test of Beery 6th ed. (VMI-6).

RESULTS

Sex was the main variable associated with the performance of the analyzed patients on TVPS-3 and VMI-6 (p<0.05); boys obtained better scores than girls in all evaluated aspects. Stereopsis was not a determinant of the patients' performance level but was associated with the far and near angles of deviation in both types of strabismus, esotropia and exotropia. Amblyopia was associated with the spatial relationship (p=0.001) and visual closure abilities (p=0.044). Form constancy skill scores diminished in both types of strabismus (esotropia: p=0.011; exotropia: p=0.004), and VMS were the most affected in patients with strabismus.

CONCLUSIONS

The performance of patients with strabismus with and without amblyopia on TVPS-3 and VMI-6 suggests that they adopt a mechanism to compensate for the impact of strabismus on their VPS and VMS.

Association of Strabismus With Functional Vision and Eye-Related Quality of Life in Children

Importance

Strabismus is common, affecting 2% to 4% of children, but how children and their families are affected in everyday life is poorly understood.

Objective

To evaluate the association of strabismus with functional vision and eye-related quality of life in children and their families using the Pediatric Eye Questionnaire (PedEyeQ).

Design, Setting, and Participants

This cross-sectional study was conducted between December 2017 and October 2019 and included 91 children with strabismus and 166 visually normal controls across 3 age groups (0-4, 5-11, and 12-17 years) who were enrolled at Mayo Clinic, Rochester, Minnesota, and Retina Foundation of the Southwest, Dallas, Texas.

Exposures

Children completed the child PedEyeQ (5 to 11- and 12 to 17-year versions: functional vision, bothered by eyes/vision, social, and frustration/worry domains); parents completed the proxy (0 to 4-, 5 to 11-, and 12 to 17-year versions: functional vision, bothered by eyes/vision, social, frustration/worry, and eye care domains) and the parent PedEyeQ (impact on parent and family, worry about child's eye condition, worry about child's self-perception and interactions, and worry about child's functional vision domains). Rasch-calibrated PedEyeQ scores were calculated for each domain and converted to 0 (worst) to 100.

Main Outcomes and Measures

PedEyeQ domain scores.

Results

Of 91 participants with strabismus, 41 (45.1%) were girls, 74 (81.3%) were white, 4 (4.4%) were Asian, 5 (5.5%) were more than 1 race, 5 (5.5%) were African American, and 2 (2.2%) were American Indian/Alaska Native. Child PedEyeQ domain scores were lower with strabismus vs visually normal controls among children ages 5 to 11 years and the greatest mean (SD) difference was in functional vision (12 [14] points; 95% CI, 6-18; P = .001), and among children ages 12 to 17 years, the greatest mean (SD) difference was in frustration/worry (27 [13] points; 95% CI, 18-36; P < .001). Proxy PedEyeQ domain scores were also lower with strabismus. The greatest difference among children ages 0 to 4 years was in functional vision (13 [9] points; 95% CI, 9-16; P < .001), among children ages 5 to 11 years was in functional vision (26 [10] points; 95% CI, 22-30; P < .001); and among children ages 12 to 17 years was in functional vision (21 [12] points; 95% CI, 12-30; P < .001), social (21 [13] points; 95% CI, 12-30; P < .001), and frustration/worry (21 [13] points; 95% CI, 12-30; P < .001). Parent PedEyeQ domain scores were lower with strabismus; the greatest difference was in worry about child's eye condition (38 [14] points; 95% CI, 34-42; P < .001).

Conclusions and Relevance

Strabismus is associated with reduced functional vision and eye-related quality of life in children. Parents of children with strabismus also experience a reduced quality of life. These findings advance our understanding of how strabismus affects children and their families and should be considered when defining patient management goals.

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.

Motor skills in children with strabismus

PURPOSE

To assess the extent to which strabismus in children was associated with motor difficulties and to examine which parameters of strabismus were most closely associated with motor development.

METHODS

The motor skills of children who were suffering from strabismus, were tested binocularly using the Movement Assessment Battery for Children, Second Edition (MABC-2) and compared with the motor performance of monocularly tested healthy controls without any ophthalmologic disease.

RESULTS

A total of 40 children with strabismus (mean, 7.25 ± 3.83 years; 19 females) and 18 controls (mean age, 8.33 ± 5.42 years; 6 females) were tested. According to the MABC-2 test, of the 40, 19 had no motor disability, and 21 were at risk of or already presented significant motor disabilities. Results of the MABC-2 were significantly lower for strabismic children without binocularity compared to those with binocularity (P = 0.002). Lack of binocularity was associated with significantly lower performance for static balance (P = 0.003) as well as for catching tasks (P = 0.042).

CONCLUSIONS

Lack of binocularity and stereopsis in children is associated with significant motor skills impairment, in particular for static balance and catching tasks. These results should be confirmed with a larger sample, including older patients, to assess the compensation mechanisms that develop with age and the actual effects of strabismus on overall motor performance.

Postural Instability in Subjects With Usher Syndrome

This study investigated postural performances and vestibular impairment in Usher patients. The three groups studied were: 11 patients with Usher type I (with visual and vestibular impairment), 14 patients with Usher type II (with only visual impairment), and 14 healthy control subjects. Postural stability was measured with a Framiral Multitest Equilibre platform with three visual conditions: eyes open (EO), eyes closed (EC), and vision disturbed by optokinetic stimulation (OPT), and two different postural conditions: stable or unstable platform. The surface and mean velocity of the center of pressure displacement (CoP) were measured and a postural instability index (PII) was calculated. Usher type I and II patients were more unstable than control subjects, but only for the unstable platform. Patients with Usher type I (with severe vestibular impairment) were also significantly more unstable than patients with Usher type II (with normal vestibular function) on the unstable platform. The severity of the vestibular impairment was correlated with the surface of the CoP displacement. We suggest that poor postural control of Usher patients is due to the abnormalities in their visual and, when defective, vestibular inputs. Measurements of postural stability on an unstable platform can distinguish type I from type II Usher patients. We emphasize the importance of multisensory evaluation in these patients to guide development of personalized visuo-vestibular rehabilitation techniques to improve their postural stability and improve their quality of life.