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Elliott DB, Foster RJ, Whitaker D, et al. Analysis of lower limb movement to determine the effect of manipulating the appearance of stairs to improve safety: a linked series of laboratory-based, repeated measures studies. Southampton (UK): NIHR Journals Library; 2015 Jul. (Public Health Research, No. 3.8.)

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Analysis of lower limb movement to determine the effect of manipulating the appearance of stairs to improve safety: a linked series of laboratory-based, repeated measures studies.

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Chapter 1Falls and stair negotiation in older people and their relationship with vision

The prevalence and morbidity of falls

Falls are a common and very serious problem for older adults, with approximately one-third of community-dwelling, healthy adults aged 65 years and over falling at least once per year, and with up to half of these people experiencing multiple falls.1 Annual falls rates increase to about 50% in people aged 85 years and over. Approximately 25% of falls result in an injury ranging from minor bruising to hip fracture.1 Hip fractures are a particularly severe consequence of falling, with the 1-year mortality rate following hip fracture being about 25%.2 In addition, 80% of surveyed older women suggested that they would rather be dead than experience the loss of independence and quality of life that results from a hip fracture and subsequent admission to a nursing home.3 Falls and hip fractures are mentioned as a contributing factor in 40% of admissions to long-term nursing and residential home care.4 Furthermore, even non-injurious falls have significant consequences, as they can lead to a fear of falling, which, in turn, results in a self-imposed restriction of functional activity, decreased mobility and independence, social isolation, deteriorating health, depression and reduced quality of life.5 Incidences of falling in older people have been consistently linked to problems with step or stair negotiation.68 In the UK, approximately 290,000 people are seriously injured and over 500 people die every year as a result of a fall on steps or stairs.7 Injuries are particularly associated with descending stairs, with associated injuries being about three times more frequent than stair ascent injuries.6 As Templer8 dramatically phrased it: ‘To fall down stairs is not only to fall off a cliff, but to fall on rocks below, for the nosing of steps presents a succession of sharp edges’.

The multifactorial nature of falls

Falls in older people are not random, chance events or ‘accidents’ but, rather, are typically multifactorial events with risk factors that include increasing age, female sex, lower-limb disabilities, impaired muscle strength, hypotension, stroke, arthritis, diabetes, cognitive impairment, Parkinson’s disease, visual impairment, sedative use, polypharmacy (taking more than four prescription medications per day) and a history of falls.4,9 The greater the number of risk factors, the more likely it is that a fall will occur, with about an 8% falls rate with no risk factors and then a 15–20% increased risk for each additional risk factor, up to 78% for four or more risk factors.9 The most common causes of fall-related injuries in older adults are trips, slips and stumbles (57%; from 2001–3 US data), with 27% being attributable to loss of balance, dizziness, fainting or a seizure.10

Visual input to balance control and mobility

Balance (or postural) control is the ability to keep the body’s centre of mass above the base of support, with inputs from the visual, vestibular and somatosensory systems being integrated centrally and instructions sent to the motor system to maintain balance. Visual input is important for both standing and dynamic balance, with optical flow providing information about anteroposterior body sway (standing)11 and heading and speed control (when walking). In addition, eye movements provide information about lateral body sway and/or lateral head movements (because lateral movement of the retinal image is automatically corrected by the vestibuloocular reflex moving the eyes in the opposite direction to the head and at the same speed).11 Vision plays a bigger part in postural control when input from the somatosensory and/or vestibular systems is disrupted.12,13 Given the importance of both central and peripheral vision plus eye movements to the control of balance, it is not surprising that balance control has been shown to be poorer with reductions in central vision, such as those caused by refractive error, cataract and age-related macular degeneration; with reduced visual field, such as that caused by glaucoma and retinitis pigmentosa; and with a variety of eye movement disorders.1217

Vision is also used to adapt gait to enable safe travel though the environment, avoiding obstacles and negotiating steps and stairs.18 Typically, vision is used to scan the travel pathway for obstacles and changes in terrain, with greater amounts of visual sampling used as the task becomes more challenging.19 This is a feed-forward or planning system and is typically used to scan one to two steps ahead20,21 with the information being kept in short-term visual memory. In addition, an online ‘fine tuning’ of gait is provided by exproprioception information (position of the lower limbs relative to the environment) from the peripheral visual system21,22 and, particularly, the lower peripheral visual field.20,22

Visual impairment and falls

Most epidemiological studies have shown that visual impairment, typically defined as binocular visual acuity worse than a Snellen score of 6/12 or 6/18 [0.30 or 0.50 logarithm of the minimum angle of resolution (logMAR)], is a significant and independent risk factor for falls, with an odds ratio of about 2.5.23 This association may be even higher given the variability that is introduced by the dependence of visual acuity scores on spectacle wear. For example, visual acuity in older people will be significantly reduced if spectacles are not worn or the wrong spectacles are worn (e.g. reading spectacles worn when walking about24); however, most epidemiological studies do not determine whether or not the participants were wearing spectacles at the time of their fall. Conversely, visual acuity can be significantly improved with updated spectacles and cataract surgery, yet there is typically no determination of whether spectacles have been updated or cataract surgery performed during most epidemiological falls studies. Such changes would reduce any link between visual acuity and falls if it occurs after initial measurements and before a fall in a prospective study or after a fall but before vision measurements in a retrospective study. Finally, changes in visual acuity may be more associated with falls than the actual level of visual acuity,25 and other aspects of vision (such as visual field assessments,26,27 contrast sensitivity and stereoacuity28) are likely to be more important risk factors than visual acuity for falls.

Clinical studies have shown that people who fall or needed hip fracture surgery have particularly poor vision. Studies have found the prevalence of visual impairment (either binocular visual acuity of 6/1229 or 6/1830,31) in older fallers attending accident and emergency (A&E) clinics to be 59%29 and 76%30 and in older people who had undergone hip fracture surgery to be 46%.31 Using estimates of older people’s A&E attendances owing to falls in 1999, Scuffham and colleagues32 estimated that these falls cost the UK government approximately £981M annually. In another publication, these authors suggested that £128M was directly attributable to falls occurring as a result of visual impairment.33 Given the increased admission rate for falls in recent years, these data are very likely to be an underestimate of the actual financial cost.

The role of vision in stairs negotiation

Typically with central vision loss, there are minimal changes seen in simple walking tasks, but caution-based movement strategies are used when task difficulty is increased and there is a greater chance of falling.34 Vision is known to have a major role in successful stair and steps negotiation,6,8,35,36 and, hence, stairs and kerbs are the most common environmental hazard associated with a fall in older people with visual impairment (30% of all hazard-related falls).37 Locating the first step edge position may be particularly problematic for older adults when lighting levels are low and/or the stair covering is patterned and/or if their vision is blurred because of visual impairment or because of viewing through part of a corrective lens used for reading.6,8,35,36,38,39 In addition to good contrast sensitivity and visual acuity, good stereoacuity may also be important to determine accurately the first step edge position. For example, improvements in stereoacuity due to cataract surgery have been found to be correlated with the change in lead-limb toe clearance when negotiating an obstacle.40

When stepping down from a raised block with blurred vision, step execution time increased, knee flexion and ankle plantar flexion increased, vertical stiffness decreased and the amount of body weight being supported by the contralateral leg increased.41 These findings suggest that, under conditions of blurred vision, participants are more cautious and attempted to ‘feel’ their way to the floor rather than ‘drop’ onto it. This may be an adaptation to increase the kinaesthetic information from the lower limb to make up for the unreliable or incomplete visual information.41 When stepping onto a raised block, blurred vision as a result of a cataract simulation has been shown to lead to a threefold safety-driven adaptation. First, to increase dynamic stability, horizontal movements of the body’s centre of mass are reduced to ensure that it is kept well within the limits of the base of support. Second, vertical toe clearance is increased to reduce the risk of tripping.38,42 Third, participants slow their forward movement, which is seen as a strategy to increase the likelihood of recovering balance should a trip occur. However, these adaptations are not straightforward. For example, although the increase in stepping time with blurred vision for both stepping up and down appears to be safety driven, it also means that the duration of single support time (the time during which the person is supported by only one limb as the other limb is swung over the step edge), which is the most dangerous period of the gait cycle, is increased. This can lead to decreases in medial–lateral stability during single-limb support, particularly with larger steps and when stepping down.43 This may help to explain why sideways falls on stairs are common in older adults, particularly with higher step heights. A sideways fall will increase the likelihood of a hip fracture. Further discussion of the role of vision in stair negotiation is provided in Chapters 2 (stair descent) and 3 (stair ascent).

Copyright © Queen’s Printer and Controller of HMSO 2015. This work was produced by Elliott et al. under the terms of a commissioning contract issued by the Secretary of State for Health. This issue may be freely reproduced for the purposes of private research and study and extracts (or indeed, the full report) may be included in professional journals provided that suitable acknowledgement is made and the reproduction is not associated with any form of advertising. Applications for commercial reproduction should be addressed to: NIHR Journals Library, National Institute for Health Research, Evaluation, Trials and Studies Coordinating Centre, Alpha House, University of Southampton Science Park, Southampton SO16 7NS, UK.

Included under terms of UK Non-commercial Government License.

Bookshelf ID: NBK305246


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