Relationship between vision and balance in static and dynamic manners

PolyU Library Call No.: [THS] LG51 .H577P SO 2016 Siongxxiv, 210 pages :illustrationsIntroduction: Fall is a common social problem in the elderly population.Any reduction in vision decreases the amount of visual information from external environment for maintaining balance and walking stability. Hence, improving older adults' visual function is one of the key elements to improve their balance function and reduces the corresponding risk of falls. Although many studies have examined the relationship between vision and balance functions, these studies had two major limitations. First, majority of these studies recruited mainly Caucasian populations, it is unclear how this relationship applies to Chinese population. Second, these studies focused on static visual function, largely ignoring the importance of dynamic visual function on balance performance. To address these limitations, 5 projects were included in this study. Project 1 investigated visual and balance performance in Chinese community-dwelling older adults using clinical screening instruments, which were developed to identify older people at high risk of falls. Age-related decline in physical fitness might affect older adults' control on body coordination. Project 2 investigated the effect of body locomotion in resolving visual stimuli moving at different speeds. Through recruiting subjects of different age groups, the interactive effect contributed by age and body locomotion in dynamic vision was also examined.. Project 3 examined the relationship between vision and balance, in particular how dynamic visual (resolving moving visual stimuli) and balance systems (weight shifting or voluntary movement responding to moving stimuli) interacted. Project 4 investigated how newly prescribed progressive addition spectacles- one of the common aids for refractive corrections in presbyopia population, affected naïve participants' vision in which influenced gait and balance performance.. Project 5 was a pilot study exploring the intervention effect of action video game on improving older adults' dynamic vision and balance functions. Methods: In Project 1, 435 Chinese older adults (age ranged from 60 to 95 years, 75.5 ± 7.2 years) in the community-dwelling were recruited. Visual function and ocular health were examined by optometric screening assessments. Balance function was assessed by Physiological Profile Assessment (PPA), including peripheral sensation, lower limb strength, coordination and sway performance (eyes close and open condition; standing on firm and foam surface). Composite fall-risk index was calculated. Participants were then followed up for falls in one year period. In Project 2, 84 healthy adults (divided into three age groups: young adults (n= 38, 25.1 ± 5.2 years), middle-aged (n= 33, 56.3 ± 6.7 years) and older-adults (n= 13, 68.9 ± 2.6 years) with normal vision were recruited to recognize visual stimuli presented at 0, 30, 60 and 90 deg/sec in 3 types of body locomotion: sitting, stepping and walking. Effects of stimuli's moving speed, type of body locomotion and age on visual acuity and contrast sensitivity were investigated. In Project 3, 40 participants (divided into three age groups: young adults (n= 16, 24.1 ± 3.9 years), middle-aged (n= 14, 56.8 ± 6.6 years) and older-adults (n= 10, 68.7 ± 3 years)) with normal vision were recruited to examine their visual and balance functions. Methodology for measuring static and dynamic visual function was similar to that in Project 2. Static balance was assessed when participant stood on firm and foam surfaces and fixated on a central target, and viewed the randomly moving targets with and without decision making accordingly. Dynamic balance was measured by limit of stability, where participants were asked to make a voluntary body movement towards eight compass directions. In Project 4, 10 naïve participants (aged from 50 to 70 years, 60.4 ± 5.3 years) without experience in wearing progressive spectacles or multifocal contact lenses were recruited. Each participant was prescribed a pair of single vision lens (SVL) and progressive addition spectacles (PAL). Visual, balance and gait functions were measured for participants wearing each pair of spectacles. Dynamic vision was assessed adopting the methodology in Project 2. Gait function was measured by Vicon Motion System, where participants walked along different paths with and without obstacles. Balance function was measured when participants stepped down onto a force platform at the end of the walk path. In Project 5, 15 adults (aged from 62 to 73 years, 66.1 ± 2.6 years) were recruited to participate in a pilot quasi-experimental study which examined the intervention effect of action video game on improving dynamic vision and balance function. Participants were randomly assigned to training (receiving 30 hours action video game training) or control groups (receiving 30 hours leisure activities). Outcome measures in dynamic vision and balance function were conducted at 4 time-point with 1-month interval.Results: Project 1 found that only 16.5% older adults' distance acuity in the better eye was worse than 6/18, which was mainly due to cataract. Compared to the Caucasian normative database, our population had "moderate" fall-risk because of the relatively larger body sway in our balance measurements. Despite the moderately high fall-risk scores, the incidence of one plus falls in the 6-month and 1-year follow-up period was only 9.6% and 17% respectively. Participants with poor distance acuity had poorer quadriceps, slower hand reaction time and poorer balance function, while the relationships were significant. In Project 2, significant main effects of target's moving speed, body locomotion and age were found on visual function. However, impacts of these 3 factors on visual function were independent, without significant interactive effect. Project 3 showed significant age-related decline in vision (static and dynamic) and dynamic balance functions. Similar to Project 1, significant relationship was found between vision and balance functions, however the relationship was stronger when both vision and balance functions were measured in dynamic status. In Project 4, no significant difference in visual (static and dynamic vision) and gait performance (in terms of head angle and required time to complete each walking cycle in the task) was found in SVL and PAL wearing. However, participants wearing the PAL required significantly longer time to stabilize and had larger body sway area (with significantly more sway along the lateral direction) after negotiating one-step down. In Project 5, no significant improvement in vision was found in both control and training groups. For balance measure, significant post-training effect was found in the postural sway along medio-lateral (M-L) and anterio-posterior (A-P) displacements when the participants fixated targets at random position or tracked a moving target. This suggested that action video-game training could potentially improve older adults' balance function in some aspects.Conclusion:Despite relatively lower prevalence of falls in Hong Kong Chinese (~17%), they had moderate fall risk score compared to Caucasian populations. Vision was one of the factors affecting balance function in a positive correlation, in particular the dynamic natures of these measures. Wearing progressive addition spectacles did not result in significant deterioration in gait function, but significantly impaired naïve wearers' balance performance. Hence, it was important to educate new wearers about this potential fall risk due to the visual disturbance induced by this type of spectacles. The significant association between age-related decline in dynamic visual and balance functions suggested that intervention for improving visual function might also result in improving balance performance. Results from our pilot study provided some preliminary evidence to support this hypothesis, where action video game training might enhance older adults' balance function. A large-scale study was required to confirm the effect of intervention.School of OptometryPh.D., School of Optometry, The Hong Kong Polytechnic University, 2016Doctorat