Gender differences and the risk of falls in individuals with profound vision loss.
Individuals with visual impairments must place a greater demand on somatosensory (the ability of the somatic senses to detect body position and maintain an upright and stable stance) and vestibular (the ability of the sensory system of the inner ear to detect rotation and acceleration to maintain a stable and up-right stance) information to establish patterns of movement when positions in space are compromised by the lack of vision or by minimal vision (Horvat, Ray, Ramsey, Miszko, Keeney, & Blasch, 2003) Previous data from the University of Texas Arlington Postural Control Laboratory indicated that vision loss results in reduced postural control (Ray, Horvat, Croce, Mason, & Wolf, 2008).The movement of individuals with visual impairments depends on the use of sensory information other than vision to initiate changes in the center of gravity and base of support prior to a movement. Although most individuals require vision to maintain postural stability, others can maintain an upright position accurately without visual information (Williams, 1983). However, balance with vision is more efficient and skillful than balance without vision, especially in changing conditions (Williams, 1983). Common problems that are associated with visual impairments are the use of other sensory and vestibular information to establish and connect movement patterns and to adjust to positions in space (Spirduso, 1995). Standing balance is diminished because the loss of vision affects the vestibular system via the lack of visual feedback (Judge, Davis, & Ounpuu, 1996; Maeda, Nakamura, Otomo, Higuchi, & Motohashi, 1998).
Adults with visual impairments experience a loss of balance and mobility, which presents a barrier to independence and is associated with the fear of falling (Crews & Campbell, 2001; Rosen, 1997; Skaggs & Hopper, 1996). The purpose of the study reported here was to determine the extent to which visual status, age, gender, body mass index (BMI), and the strength of quadriceps and hamstrings contribute to compromised postural control in adults with visual impairments. Establishing these relationships is an important prerequisite to identifying at-risk subpopulations and the future development of evidence-based therapeutic prescriptions that are aimed at maintaining or improving postural stability in these adults.
METHODS
Participants
Sixty-five adults (aged 20-65) were recruited from the Dallas-Fort Worth chapters of the American Foundation for the Blind, National Federation of the Blind, and Lighthouse for the Blind of Fort Worth. The participants were divided into three categories (low vision, medium vision, and sighted) using the classification system of the International Blind Sports Association (2008). Participants in the low vision category had up to light perception, but an inability to see shapes, consistent with the partial sight permitted in the B1 sports classification of athletes who are blind. Participants in the medium vision category were able to recognize hand movements up to and including 2/60 (20/600) acuity, or a visual field limited to less than 5 degrees. Participants in the sighted category were those with typical age-related vision loss, a corrected vision that exceeded 20/32, and no visual field loss. These three levels represent a functionally relevant transformation of LogMAR (logarithm of the minimum angle of resolution) acuities and visual fields. Height and weight were collected from all the participants to calculate their BMIs. Visual classifications, sample sizes, BMIs, determinants, and demographic characteristics are presented in Table 1. The institutional review board at the Dallas VA Medical Center approved this study, and informed consent was obtained from the participants.
Measure of postural stability
The Sensory Organization Test (SOT) of the NeuroCom Equitest System (NeuroCom International, Clackamas, Oregon) provides information on the use of sensory input or a combination of inputs to maintain postural stability. Inaccurate information is delivered to the eyes, feet, and joints through sway referencing of the visual surround (walls) and support surface (NeuroCom International, 2001). This alteration disrupts the available sensory information and allows the tester to isolate visual, somatosensory, and vestibular systems that provide afferent information to maintain postural control (Guskiewicz, Riemann, Perrin, & Nashner, 1997). With this technique, it is possible to determine how an individual uses changing sensory information from the sway-referenced senses. It should be noted that sensory information may be accurate or inaccurate under different conditions (see Table 2). For example, in Condition 1, vestibular, visual, and somatosensory information is accurate, while in Condition 6, only vestibular information is accurate.
The NeuroCom system uses a force platform and measures vertical reaction forces that are generated from the participants' center-of-pressure movement from a fixed base of support and transducers embedded in the force platform (Guskiewicz et al., 1997). SOT assesses the angle of each participant's center-of-gravity sway by measuring the angle between a projected vertical line from the participant's center of support and a projected vertical line to his or her center of gravity. This value (degrees/second sway) is then compared to the participant's theoretical maximum displacement, and the results are expressed as a score between 0 and 100. Scores that are close to 0 denote sway amplitudes that are close to the individual's limit of stability, while a score of 100 equals perfect stability (NeuroCom International, 2001). A fall results in a score of 0 for the trial (NeuroCom International, 2001).
The participants were tested under six conditions with three trials per condition. Each of the 18 trials lasted 20 seconds, with the composite score calculated using the peak value (least sway) from Conditions 1-3 and the mean value from Conditions 4-6 (NeuroCom International, 2001). If the participant had to make constant adjustments to maintain postural stability (increased sway), the score for that trial would decrease, depending on the amount of sway in the trial. Higher scores reflected less movement (greater postural stability or less sway). Conditions 1, 3, 4, and 6 were performed with the eyes open, while Conditions 2 and 5 were performed with the eyes closed (see Table 2). The eyes open and closed conditions were included to accommodate those individuals with some remaining vision. This approach enabled us to analyze the extent to which remaining vision is used to maintain postural stability. The sensory system thats were targeted by the NeuroCom Equitest, along with the group scores for each condition, are presented in Table 2.
Measure of the strength of quadriceps and hamstrings
A Cybex Isokinetic Dynamometer was used to measure the isokinetic strength of the participants' knee extensors and flexors throughout the full range of motion with the angular velocity set at 90 degrees per second. Torque values were corrected for the effect of gravity (Fillyaw, Bevins, & Fernandez, 1986). This procedure was repeated for six continuous extension-flexion repetitions. No rest was allowed between repetitions. The peak values were identified as the highest recorded values.
PROCEDURES
Before the data were collected, the participants underwent 5-10 minutes of supervised stretching exercises for their upper and lower extremities that were led by a member of the research team with credentials from both the National Athletic Trainers Association and the National Strength and Conditioning Association. Evaluations of the SOT were conducted with the participants harnessed to eliminate the risk of falling and to permit maximal sway (NeuroCom International, 2001).
Prior to the strength testing, the participants practiced knee extension and flexion movements with the dynamometer at 90 degrees per second throughout the active range of motion. The testing protocol, positions, and joint stabilization conformed to the guidelines for isokinetic testing (Perrin, 1993). All strength and power repetitions were performed with the arms folded across the chest. The participants performed two sets of six repetitions. They were verbally exhorted to exert maximal effort in performing these repetitions in a manner that was consistent with earlier investigations (Perrin, 1993).
Data analyses
A multiple regression analysis was performed to examine the contribution of visual status, age, gender, BMI, and the strength of quadriceps and hamstrings to postural stability (SOT composite score) in the participants. The standardized beta values were used to rank the relationships between the variables and the SOT composite score, and the unstandardized beta scores indicated the amount of change related to each variable. The initial model included all the data on the participants (visual status, age, gender, BMI, strength of the quadriceps, and strength of the hamstrings), with the final model consisting of only visual status and gender. Follow-up univariate analyses of variance were performed to analyze between-group (visual status) and within-group (gender) differences on the SOT composite score and the strength of quadriceps and hamstrings. The criterion level for significance was set at p < .05. SPSS version 15.0 statistical software was used to analyze all the data.
RESULTS
The results from the initial multiple regression analysis showed that the two contributors to decreased postural stability were visual status (beta = -.318) and gender (beta = -.299). The results of the regression analysis indicated no significant relationships between postural stability and the participants' BMI, strength of quadriceps and hamstrings, or age. The multiple regression analysis found a significant relationship between the predictors (visual status and gender) on postural control (the SOT composite score): F (2, 64) = 8.33, p = .001). The effect of visual status on postural control resulted in a change of -2.76 [+ or -] .92 SOT composite units (t = -3.00, p = .004) for each unit change in the visual status classification. The impact of gender on postural stability resulted in a change of -5.95 [+ or -] 2.45 SOT composite units (t = -2.43, p = .018) associated with being female. The final model, consisting of visual status and gender, resulted in an r = .50 (SEE = 9.39), accounting for 25.1% of the total variance. The mean SOT composite score was 80.7 [+ or -] 5.40 and 73.9 [+ or -] 14.9 for the men and women, respectively. The only significant within-group difference on the SOT composite score was found in the participants in the low vision category: F(1,13) = 7.46, p = .018, with men scoring higher than women. Visual status had a correlation of -.339 (p = .006) with the overall SOT composite score; however, the only condition with a significant relationship between visual status and postural instability was the performance of the visually impaired group in Condition 4 (r = -.545, p < .001) of the NeuroCom SOT. Between-group differences for Condition 4 resulted in an F(2, 64) = 4.02, p = .023. For Condition 4, the mean value for the sighted group was 84.5 [+ or -] 7.39, for the medium vision group was 73.4 [+ or -] 12.7, and for the low vision group was 63.6 [+ or -] 17.1. Isokinetic strength testing yielded no differences among the groups (p > .05), and when the peak torque was normalized for body weight, no gender differences (p < .05) were found.
DISCUSSION
The results of this study provide evidence that postural stability is disproportionately reduced in women with vision loss. On the basis of the data analyses, although decreased visual status apparently contributes to postural instability, the predominant contributing factor to this instability is inaccurate somatosensory information (Condition 4), which primarily affects postural control in women. This result is noteworthy because by identifying women with vision loss as being disproportionately at risk for decreasing postural stability, fall-prevention programs can target women with declining vision.
The analyses indicated that women with profound vision loss are apparently more likely than are men with vision loss to show a greater decline in postural control. Furthermore, since profound vision loss leads to self-imposed restrictions in activity and the avoidance of risky behaviors (such as climbing stairs; see Ray et al., 2008), vision loss has a profound impact on individuals' lifestyles, and the data lend support to the notion that women are affected more severely than are men, thereby providing a rationale for rehabilitation interventions that focus on preserving or improving postural control in women with declining vision.
CONCLUSION
Many factors contribute to postural stability among individuals with profound vision loss. Given the negative impact that reduced vision has on activity levels, there is a compelling need to define better and provide evidence-based approaches to maintain postural control in older adults who are making the transition to profound vision loss. The results of this study provide support for physiotherapeutic rehabilitation interventions that target women with visual impairments as an area of need for balance rehabilitation. Stevens and Sogolow (2005) reported that women are 2.2 times more likely than are men to suffer from fractures resulting from falls. Their finding, together with the data from this study, provide compelling evidence to support further research on the risks of aging and vision loss. Specifically, studies should be undertaken to identify if women with profound vision loss are at an increased risk of developing sarcopenia or osteoporosis or to become frail later in life. Additional research should focus on the systematic evaluation of appropriate therapeutic exercise to enhance functioning in women with declining vision.
REFERENCES
Crews, J., & Campbell, V. (2001). Health conditions, activity limitations, and participation restrictions among older people with visual impairment. Journal of Visual Impairment & Blindness, 95, 453-467.
Fillyaw, M., Bevins, T., & Fernandez, L. (1986). Importance in correcting peak torque for the effect of gravity when calculating knee flexor to extensor ratios. Physical Therapy, 66(1), 23-29.
Guskiewicz, K. M., Riemann, B. R., Perrin, D. H., & Nashner, L. (1997). Alternative approaches to the assessment of mild head injury in athletes. Medicine & Science in Sport and Exercise, 29, 213-221.
Horvat, M., Ray, C., Ramsey, V. K., Miszko, T., Keeney, R., & Blasch, B. (2003). Compensatory analysis and strategies for balance in individuals with visual impairments. Journal of Visual Impairment & Blindness, 97, 695-703.
International Blind Sports Association. (2008). IBSA medical classification. Retrieved from http://www.ibsa.es/docinteres/HTN/MedicalClassification.htm
Judge, J. O., Davis, R. B., & Ounpuu, S. (1996). Step length reductions in advanced age: The role of ankle and hip kinetics. Journal of Gerontology, 51A, M303-M312.
Maeda, A., Nakamura, K., Otomo, A., Higuchi, S., & Motohashi, Y. (1998). Body support effect on standing balance in the visually impaired elderly. Archives of Physical Medicine and Rehabilitation, 79, 994-997.
NeuroCom International. (2001). NeuroCom system operators manual. Clackamas, OR: Author.
Perrin, D. H. (1993). Isokinetic exercise and assessment. Champaign, IL: Human Kinetics.
Ray, C., Horvat, M., Croce, R., Mason, R. C., & Wolf, S. (2008). The impact of vision loss on postural stability and balance strategies in individuals with visual impairments. Gait & Posture, 2, 58-61.
Rosen, S. (1997). Kinesiology and sensorimotor function. In B. Blasch, W. R. Wiener, & R. L. Welch (Eds.), Foundations of orientation and mobility (2nd ed., pp. 456-482) New York: American Foundation for the Blind.
Skaggs, S., & Hopper, C. (1996). Individuals with visual impairment: A review of psycho-motor behavior. Adapted Physical Activity Quarterly, 13(1), 16-26.
Spirduso, W. W. (1995). Aging and motor control. In D. R. Lamb, C. V. Gisolfi, & E. Nadel (Eds.), Exercise and older adults (pp. 58-59). Carmel, IN: Cooper Publishers.
Stevens, J. A., & Sogolow, E. D. (2005). Gender differences for non-fatal unintentional fall-related injuries among older adults. Injury Prevention, 11, 115-119.
Williams, H. (1983). Perceptual and motor development. Englewood Cliffs, NJ: Prentice Hall.
This study was funded by the Department of Rehabilitation Research and Development, Department of Veterans Affairs.
Christopher T. Ray, Ph.D., ATC, CSCS, assistant professor, Department of Kinesiology, University of Texas at Arlington, Box 19259, 111 Maverick Activities Center, Arlington, TX 76019-0259; email: <chrisray@uta.edu>. Steven L. Wolf, Ph. D., P.T., professor, Departments of Rehabilitation Medicine, Medicine, and Cell Biology, Emory School of Medicine, 1441 Clifton Road, NE, Atlanta, GA 30322, and research physiologist, Atlanta VA Rehabilitation and Development Center, 1670 Clairmont Road, Decatur, GA 30033; e-mail: <swolf@emory.edu>.
Table 1
Demographic characteristics of the participants (N = 65).
Characteristics Sighted Medium vision
Number of participants 29 18
Males 19 12
Females 10 6
(M [- or -] SD) (M [- or -] SD)
Age 44.4 [- or -] 14.7 49.5 [- or -] 11.9
Height (in meters) 1.74 [- or -] 9.57 1.73 [- or -] 11.7
Weight (in kilograms) 78.6 [- or -] 16.6 87.9 [- or -] 20.8
BMI 25.7 [- or -] 3.51 29.4 [- or -] 4.87
Quadriceps strength 94.9 [- or -] 55.5 88.6 [- or -] 58.6
(PT, BW)
Hamstring strength 63.1 [- or -] 40.7 49.6 [- or -] 32.8
(PT, BW)
Characteristics Low vision
Number of participants 18
Males 9
Females 9
(M [- or -] SD)
Age 42.4 [- or -] 13.1
Height (in meters) 1.70 [- or -] 12.7
Weight (in kilograms) 88.3 [- or -] 26.5
BMI 31.1 [- or -] 9.93
Quadriceps strength 87.4 [- or -] 48.0
(PT, BW)
Hamstring strength 51.3 [- or -] 30.6
(PT, BW)
Note: PT = peak torque.
Table 2
Available sensory information and participants' scores, by condition.
Variables Condition 1 Condition 2
Accurate sensory Vestibular Vestibular
information Vision Somatosensory
Somatosensory
Sensory information Accurate Accurate
Eye condition groups Open Closed
(M [+ or -] SD) (M [+ or -] SD)
Sighted
Males 96.2 [+ or -] 2.89 95.3 [+ or -] 6.2
Females 97.7 [+ or -] 2.26 98.1 [+ or -] 1.00
Medium vision
Males 96.8 [+ or -] 2.48 96.6 [+ or -] 2.00
Females 96.9 [+ or -] 2.43 97.3 [+ or -] 2.04
Low vision
Males 97.8 [+ or -] 1.34 97.7 [+ or -] 1.52
Females 96.3 [+ or -] 3.11 96.3 [+ or -] 3.32
Variables Condition 3 Condition 4
Accurate sensory Vestibular Vestibular
information Somatosensory Vision
Sensory information Inaccurate Inaccurate
Vision Somatosensory
Eye condition groups Open Open
(M [+ or -] SD) (M [+ or -] SD)
Sighted
Males 95.0 [+ or -] 8.58 82.3 [+ or -] 7.98
Females 98.5 [+ or -] 1.06 88.7 [+ or -] 3.55
Medium vision
Males 96.7 [+ or -] 2.50 69.5 [+ or -] 14.1
Females 96.5 [+ or -] 3.99 80.2 [+ or -] 10.6
Low vision
Males 97.6 [+ or -] 1.52 69.2 [+ or -] 13.7
Females 96.1 [+ or -] 3.66 63.0 [+ or -] 18.3
Variables Condition 5 Condition 6
Accurate sensory Vestibular Vestibular
information
Sensory information Inaccurate Inaccurate
Somatosensory Vision and
Somatosensory
Eye condition groups Closed Open
(M [+ or -] SD) (M [+ or -] SD)
Sighted
Males 67.2 [+ or -] 15.5 76.8 [+ or -] 10.5
Females 79.1 [+ or -] 7.80 84.9 [+ or -] 5.88
Medium vision
Males 67.6 [+ or -] 14.5 72.3 [+ or -] 8.37
Females 74.0 [+ or -] 14.1 81.6 [+ or -] 9.55
Low vision
Males 77.3 [+ or -] 5.25 78.2 [+ or -] 6.78
Females 64.9 [+ or -] 25.7 67.8 [+ or -] 24.1
SOT
Variables Composite
Accurate sensory
information
Sensory information
Eye condition groups (M [+ or -] SD)
Sighted
Males 81.2 [+ or -] 5.76
Females 83.1 [+ or -] 3.11
Medium vision
Males 79.4 [+ or -] 4.50
Females 75.7 [+ or -] 8.36
Low vision
Males 81.3 [+ or -] 6.02
Females 62.7 [+ or -] 19.1
SOT = Sensory Organization Test.
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| Title Annotation: | Research Reports |
|---|---|
| Author: | Ray, Christopher T.; Wolf, Steven L. |
| Publication: | Journal of Visual Impairment & Blindness |
| Article Type: | Report |
| Geographic Code: | 1USA |
| Date: | May 1, 2010 |
| Words: | 3108 |
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