INTRODUCTION AND PURPOSE
Balance refers to the dynamics of body posture aimed at preventing falls and is a requisite for execution of movement and successful completion of functional activities.1 As the postural control system requires information from the visual, vestibular, and proprioceptive systems, a lack or insufficiency of visual input influences the ability to maintain balance.1,2 Therefore, people with visual impairment (VI) have been reported to have deficient balance compared with individuals without VI.3–12
Some earlier studies indicate that the lack of visual information can be partially compensated by the increased use of residual sensory systems to maintain balance in individuals with vision loss.3,7 In a study by Ribadi et al,3 adolescents with congenital blindness outperformed their blindfolded peers without VI in dynamic balance tasks. Another study revealed that in adolescents with total blindness, postural control is better than in subjects who are legally blind and individuals who are blindfolded but without VI, which may indicate that people with total blindness develop superior proprioceptive and vestibular reactions.7 However, in other research, the outcomes of individuals without VI being blindfolded during balance tasks did not differ from that of subjects with VI or were even better than that in people with vision loss.5,6,8,11,12
People with blindness and low vision use different strategies to stabilize the body in space than those used by individuals without VI. However, it remains unclear whether those behaviors are related to an adaptive compensatory strategy or inefficiency of movements increasing the risk of fall in subjects with blindness and low vision.8,11,13 For example, Schmid et al8 noted significantly larger body displacement with a stronger coupling between segments during dynamic posturography in adults with blindness. The larger body displacement may be a means of getting stronger vestibular input for balance control or a sign of increased postural anxiety as a consequence of poor balance. In other studies, Horvat et al13 and Ray et al11 reported an increased use of the hip strategy in subjects with VI, possibly related to difficulties in anticipatory balance adjustments, ankle muscles weakness, or simply cautiousness in their movements.
Because studies reveal that the balance ability in people with VI is generally worse than that in subjects without visual deficits and apparently experience alone cannot fully compensate for the lack or insufficiency of visual information,3–12 appropriate interventions may contribute to the improvement of balance abilities in subjects with VI.14
In the pediatric population, VI acts as a constraint on overall development, affecting indirectly the acquisition of gross motor skills because of reduced incentive and opportunities for movement, difficulties in learning through imitation, as well as fear. Thus, children and adolescents with VI often experience delays in various aspects of motor development and are at risk for postural abnormalities.4 Therefore, the physical therapist is commonly a member of the educational team for children and adolescents with VI.
In childhood, VI leads to different motor problems, and according to some authors, balance is most affected in gross motor skills.4 Therefore, children and adolescents with VI were reported to have worse performance in both static and dynamic balance tasks than their peers without VI.3,4,6,7,9,10 Those findings were based on laboratory balance measurements3,7 and norm-referenced tests of motor proficiency, such as the Bruininks-Oseretsky Test of Motor Proficiency4 and the Movement Assessment Battery for Children (MABC),9,10 or commonly used clinical balance tests (Flamingo Balance Test).6 However, the functional relevance of those measures is not directly interpretable. Although comparative studies reveal that balance abilities in children and adolescents with blindness and low vision are inferior to that of their peers with typical development, the studies do not reveal whether those findings imply functional limitations. To our best knowledge, the only attempt to relate the results of balance assessment in children with VI to their performance of daily activities was made by Engel-Yeger.9 In that study, the parents of children with unilaterally reduced vision (aged 4-7 years) were asked to rate the frequency of everyday situations that reflect the children's balance and posture abilities as well as intolerance or hypersensitivity to movement on a 5-point Likert scale. Significant correlations were found between some items on a parent's questionnaire composed for the study and mean balance scores of children on the MABC and between mean score of items that evaluate static balance in the parent's questionnaire and mean score of MABC static balance items.9 Nevertheless, on the basis of previous studies, the effect of balance deficits in subjects with VI on carrying out activities of daily living cannot be determined.
Identification of functional problems enables physical therapists and specialists in adapted physical education to concentrate on the areas of particular need and to implement adequate interventions. Thus, understanding the level of functioning of children and adolescents with VI may lead to more effective physical therapy and physical education programs. Although the major problems affecting everyday life of children and adolescents with VI, especially locomotor activities, are spatial orientation, locating objects in space, and anticipation of danger, we suggest that poor balance abilities may increase difficulties in independent mobility in this population. Moreover, identifying the effects of VI on functional activities may give some insight into treatment approaches for children and adolescents with multiple disabilities. Since most children and adolescents with VI have additional motor, sensory, or cognitive impairments, they are commonly seen in physical therapy practice. Working with children with VI poses a unique challenge; therefore, physical therapists should be aware of problems related to the lack or insufficiency of visual information. The purpose of this study was to examine functional balance abilities of girls with VI. Since there are no specific tools to evaluate functional balance abilities in children and adolescents with VI, the study also aimed to compare the results of clinical balance assessment and quantitative measurement of balance with stabilography.
Twenty-six girls with VI aged 10 to 15 years (mean = 12.7, SD = 1.8) participated in this study. Following the World Health Organization definition of VI, the inclusion criterion was a best corrected visual acuity of less then 0.3 or 20/60, which means that the eye with better visual acuity provides vision from a distance of 20 ft that is equal to what an individual without VI can see at 200 ft. For the World Health Organization International Classification of Diseases, Tenth Revision, classification of VI, see Table 1.15 The degree of VI of each participant with respect to the World Health Organization International Classification of Diseases, Tenth Revision, classification is reported in Table 2. The visual status ranged from severe VI to total blindness. The cause of VI included retinopathy of prematurity, optic nerve abnormalities, congenital cataract, anophthalmia, and retinoblastoma. Visual impairment was congenital or acquired (see Table 2). Children and adolescents with physical and/or intellectual disability were excluded from this study. Data concerning visual status were extracted from medical records.
The study protocol was approved by the local bioethics committee. Written informed consent was obtained from each participant's parent or guardian before data collection.
The Pediatric Balance Scale (PBS), which is a modification of Berg Balance Scale (BBS) designed for children and adolescents aged 5 to 15 years, was chosen to assess functional balance abilities in girls with VI. The PBS examines various activities that a child must perform to safely and independently function at home, at school, and in the community. The scale was developed to assess both static and dynamic balance, including tasks requiring anticipatory balance and self-induced challenge to limits of standing stability.16,17 The PBS enables an assessment of balance abilities in the context of everyday tasks and requires only minimal use of specialized equipment. The scale is composed of 14 items that are scored on a criterion-based 0 to 4 scale (see Table 3). The range of scores in the PBS is 0 to 56. The test-retest and interrater reliability of the PBS was found to be high (intraclass correlation coefficient = 0.998 and 0.997, respectively) in school-aged children with mild to moderate motor impairment.16 As, to our knowledge, the PBS has not yet been used to assess balance in children with sensory impairments, we used stabilography to examine concurrent validity of the scale for assessment of balance abilities in children and adolescents with VI. Postural stability was measured during 30-second quiet stance in a natural posture on a force platform (80 cm × 80 cm). The force platform was linked to a personal computer via a 4-channel amplifier with a 12-bit analog-to-digital converter. The signals from the load cells were amplified and converted from analog to digital form and then recorded on the computer using a software program that calculated the center-of-pressure trajectory in relation to the platform coordinates. Data were sampled at 20 Hz. The calculated parameters were sway path and average sway velocity, as well as mediolateral and anterioposterior sway path, average sway amplitude, and velocity.
At the beginning of the test session, height and weight were measured and recorded for each participant. Stabilography and the PBS were performed by each subject in random order during a single test session that lasted approximately 30 minutes. The PBS was administered to each girl individually, using a protocol and scoring described by Franjoine et al.16 Although the scale was developed for children with motor impairment, the items clearly relate to activities of daily life and the examiner is authorized to use verbal and physical prompts to clarify tasks, so adaptations were not needed for children and adolescents with VI. Moreover, each girl was allowed to feel the test materials before the test was administered. The stabilometric measurement was performed during 30 seconds of quiet stance with feet hip-width apart and arms freely hanging on both sides. Assistance was given to enable each child to achieve a proper position in the center of the force platform.
The participant was asked to stand as still as possible. Data recording started once the subject was stable in the required posture and stated that she was ready. All data were collected in a quiet room free from external distractions at the Educational Center for Blind Children in Laski.
To describe the study group, means and standard deviations were calculated for age, height, and weight. The mean, standard deviation, and range of the PBS total test scores, as well as the percentage of participants attaining scores from 0 to 4 in each PBS item were reported. Spearman rank correlation analyses were performed to determine the associations between PBS total test scores and all of the sway parameters. The α level was set at .05. The statistical analyses were performed using Statistica software (version 9.0).
The age, degree, cause, and onset of VI, as well as PBS total point scores for all of 26 girls who participated in this study are presented in Table 2. The mean height in study sample was 151.8 cm (SD = 11.7 cm) and the mean weight 45.3 kg (SD = 11.9 kg). The range of point scores on the PBS was 47 to 56 (mean = 52.6, SD = 2.2). Although all participants (n = 26) demonstrated mastery in 9 of 14 PBS items, the maximal score on the scale was achieved only by 11.5% (n = 3) of the study sample. As seen in Table 4, the greatest difficulties in maintaining balance appeared in single-limb stance; 88.5% of participants (n = 23) were not able to hold the position for 10 seconds or more, and in 46.2% of participants (n = 12), single-limb stance time was less than 3 seconds. Fifteen (57.7%) of the subjects demonstrated difficulty in reaching forward with an outstretched arm in standing, and 53.8% of participants (n = 14) could not maintain tandem stance for 30 seconds. In 2 cases (7.7%), some difficulties occurred in dynamic balance tasks such as turning 360° and alternately placing a foot on a step stool while standing unsupported.
The results of stabilography are presented in Table 5, whereas Table 6 provides Spearman rank correlation coefficients between total point scores in the PBS and sway parameters. There was a statistically significant correlation (P < .05) between PBS total point scores and sway path, average sway velocity, sway path in the anterioposterior direction, as well as average sway velocity in the mediolateral direction, with r values ranging from −0.44 to −0.48. The strongest relationship was found between PBS scores and sway path in the mediolateral direction (r = −0.58, P < .005), as well as average sway amplitude in the mediolateral direction (r = −0.57, P < .005). The correlation between PBS scores and stabilographic parameters in the anterioposterior direction, such as average sway amplitude and velocity, was weak and not significant.
In previous studies, balance abilities of children and adolescents with VI were compared with those of their peers with no impairments. The main finding was that children and adolescents with VI perform worse than their peers with typical development on both static and dynamic balance tasks.3,4,6,7,9,10 However, those deficits have not been analyzed in the context of activities of daily living. Therefore, the difference compared to the groups without VI may not imply that this discrepancy affects everyday functioning of children and adolescents with VI.
Although all participants aged 10 to 15 years demonstrated mastery in 9 of 14 items of the PBS, only 11.5% of the group achieved the maximal score on the scale. Results of previous studies indicate that the PBS reflects development of balance control in children with typical development and that they achieve the maximal score by the age of 9 years.18 According to Franjoine et al,17 30.3% of children without impairments achieve the maximal point score on the PBS by the age of 5 years, and in children and adolescents aged 7 to 13 years, this percentage reaches 69.1%. Thus, the present study seems to provide further evidence that children and adolescents with VI have deficits in balance control compared with their peers with no VI.
In this study, a moderate negative correlation (correlation coefficients between −0.4 and −0.6) was found between the PBS total point scores of girls with VI and most of the stabilographic parameters. Correlation between stabilographic and clinical measurement of balance with the BBS, considered as the reference standard for functional balance assessment in adults, with an average value of −0.55,19 is similar to that obtained in the present study. Thus, results of correlation analysis between the PBS and stabilography seem to provide some evidence of concurrent validity of the PBS in balance assessment of girls with VI. However, the relationship between PBS total point score and sway parameters in the anterioposterior direction such as average sway amplitude and velocity was not significant. Since, to our best knowledge, there were no studies that compared results of the PBS with that of stabilography in children with typical development, it is not clear whether those results are specific for the population of the children and adolescents with VI or are because of the construction of the scale itself, which may be more sensitive in identifying balance deficits in the frontal plane. However, the comparisons of static posturography and the BBS, which was a basis for development of the PBS, revealed that the BBS correlates better with anterioposterior parameters and the speed of anterioposterior sway differentiates among subjects walking with and without aids.19 Thus, the fact that in the present study, the correlation between PBS scores and most of the stabilographic parameters in the sagittal plane was not observed may be attributed to the characteristics of the sample, which was relatively homogenous with respect to balance abilities, being composed of subjects who walked independently.
Another finding was that functional balance abilities in girls with VI correlate most with stabilographic parameters in the frontal plane, such as mediolateral sway path and average sway amplitude. Some evidence in the literature indicates that postural control in the frontal plane depends more on proprioceptive information, whereas in the sagittal plane, we rely more on visual cues.2,12 Moreover, mediolateral stability in blind athletes was found to be better than in people with blindness who were not involved in sports activities.5 Therefore, we can hypothesize that appropriate interventions could contribute to the improvement of functional balance abilities in children and adolescents with VI. Nevertheless, results of the present study should be interpreted with caution, given the small sample size that may not be representative of children and adolescents with VI.
The study highlights functional problems of children and adolescents with VI by using the PBS to examine the abilities that are crucial to safely and independently meet the demands of everyday tasks, that is, changing positions, maintaining position within a decreasing base of support, and reaching beyond one's base of support. Moreover, this study seems to provide some evidence on the validity of the PBS as an assessment tool in this population. However, before the scale is recommended for use in screening, as well as in planning and evaluating the effectiveness of interventions, other psychometric properties of the PBS in this population need to be examined.
Girls with VI aged 10 to 15 years appear to have no difficulties in balance control in the sitting position, during transfers, and quiet standing. Nevertheless, problems occur in the standing position when the size of the base of support is narrowed, as well as in situations where the center of gravity is approaching the edge of the base of support. This situation occurs in 1 of the items of the PBS consisting of reaching forward with an outstretched arm. Identification of those deficits in an isolated clinical setting, using a scale based on everyday tasks, suggests that these may appear in situations of daily living, when people with VI are confronted with an environment that is constantly changing. As vision is a basic and the most accessible source of information about the environment, which enables an ongoing process of updating environmental information, as well as calibration of other sensory systems, children and adolescents with VI are more adversely affected by changing conditions.20 Thus, difficulties in maintaining balance that were identified in this study can be enhanced by lowered illumination, the presence of motion, as well as an unfamiliar environment, when walking on uneven surfaces or while negotiating common indoor and outdoor obstacles.
The results of this study demonstrate that VI itself can lead to balance problems, which may affect everyday functioning. This is an important issue that should be taken into consideration by physical therapists, given the high prevalence of VI among children and adolescents with motor impairments or intellectual disability. It seems that VI would further enhance motor problems in these populations.
The present study has some limitations that must be taken into consideration when interpreting the results. One limitation of the study is the small sample size, which is because of the low incidence of blindness and low vision among children and adolescents. Furthermore, as in most studies on VI, subjects were not homogenous in their level of vision and type of eye condition. In future studies, factors such as age, gender, physical fitness level, as well as the degree and cause of VI should be included in the analysis of functional balance abilities in children and adolescents with blindness and low vision to determine which of those variables should be taken into account when developing and implementing interventions to improve their everyday functioning. Moreover, the efficiency of different interventions in improving functional abilities in children and adolescents with VI should be verified.
The level of balance of girls with VI is sufficient for independent sitting, standing, and transfers. Nevertheless, girls with VI have difficulties in balance control in the standing position when the base of support is narrowed as well as in situations where the center of gravity is approaching the edge of base of support. Those deficits in balance control may appear in more complex activities of daily life and in unfamiliar environments, which indicates a need to provide interventions to improve the functional balance abilities of children and adolescents with VI. The present findings need to be confirmed by further studies.
The authors thank all the girls who participated in this study and their families.
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