to compensate for age-related sensorimotor declines, but as we age, cortical shrinking occurs, synaptic connections become more inefficient, and neurotransmitter amount and usage declines. This all spells trouble for an older adult who is attempting to carry a heavy load from an unfamiliar store to their car in the dark, while talking to a friend. Performing multiple tasks in new or challenging situations is a recipe for falls in many older adults, especially those with presence of disease or comorbidities that affect postural control. The paradox of this aging dilemma is that the prefrontal structures required to maintain balance and cognitive control show the largest age- related differences. Older adults are relying on diminishing CNS cognitive resources, thus are at increased risk for falls. Specific screening techniques for changes in postural control will be addressed in a later section and will include tests such as the modified Clinical Test for Sensory Interaction in Balance, the Timed Up and Go (TUG) Cognitive test, and the BestTEST. Sensory changes Although all senses are affected by aging to some degree, those that most directly affect fall risk include vision, somatosensation, and vestibular function. These senses should provide the CNS with an accurate picture of where the body is in space and whether it is stationary or in motion (Shumway-Cook & Woollacott, 2007). When all three senses are working normally, adults should have adequate postural control for a variety of tasks and environments through the ability of the CNS to modify reliance on a particular system, also called sensory reweighting (Oie, Kiemel, & Jeka, 2002). This sensory weighting hypothesis suggests that the CNS integrates all sensory input and then decreases the “weight” or attention given in inaccurate sensory inputs during a postural control task, while increasing weight or attention given to more accurate senses. Age-related changes in vision, somatosensation, and/or vestibular input can influence sensory integration demands on the CNS and should be considered during a fall risk assessment for older adults. Other senses such as hearing, taste, and smell have a lesser impact on fall risk, but are discussed here as they may indirectly affect safety and nutrition. Vision Aging is associated with loss of visual acuity, development of cataracts, macular degeneration, glaucoma, and other less common visual conditions that increase risk for falls. Overall visual acuity diminishes; presbyopia or “near vision” is decreased; pupil diameter decreases, reducing light to the retina by one-third that of younger adults; lens yellowing increases, which decreases light and increases glare; contrast sensitivity declines, making it difficult to see in dimly lit settings; impairments in depth perception occur; and a general loss in the visual field occurs. The overall result for older adults is an increased need for more light to see clearly and function safely. Adults who report problems or have abnormal visual screening results should be referred for a formal vision assessment. It is unclear whether visual correction alone will decrease risk for falls, but the literature is clear that vision assessment and correction should be part of a multifactorial fall risk intervention (AGS/BGS, 2010). Somatosensory system Older adults experience somatosensory changes that can be attributed to typical aging or to conditions such as diabetes mellitus or spinal stenosis. Older adults can experience up to a 30% decline in cutaneous sensitivity due to normal aging, along with a decline in vibratory sensitivity that can change as much as three times the normal amount by 90 years of age (Shumway-Cook & Woollacott, 2007). Additionally, pain and temperature sensitivity can become less acute and proprioception and position sense can decline with age. Declines in nerve conduction velocity also may result from aging in the peripheral nervous system (PNS) and the CNS. The basic result for older adults is some degree of peripheral neuropathy in various sensory modalities, depending on the presence of comorbidities in union with the aging process.
Although existing clinical guidelines do not address assessment of somatosensation, clinicians should screen for the presence of sensory loss, especially in the soles of the feet. These sensory changes in the foot may lead to unsafe choices in footwear, which can contribute to fall risk (AGS/BGS, 2010). Most studies recommend a foot assessment that identifies the presence of serious foot problems such as severe bunions, toe deformities, ulcers or deformed nails, or changes in position sense. This also should include an assessment of the quality and appropriateness of footwear. Vestibular system The vestibular system’s job is to estimate body and head position and motion (Herdman & Clendaniel, 2014). It provides structures in the CNS, such as the cerebellum and vestibular nuclear complex, with inputs from the inner ear, proprioception from the areas such as the cervical spine, visual signals, and motor intentions to help generate accurate motor commands. This system is normally very accurate. Unfortunately, declines in the effectiveness and accuracy of the vestibular system affect almost all older adults. By 70 years of age, the typical adult experiences a 40% loss of vestibular hair and nerve cells. These PNS structures help to detect changes in head motion, which are crucial for normal postural control. These changes also are accompanied by 3% loss per decade of vestibular nucleus cells in the CNS that occur from 40 to 90 years of age. As older adults experience reduced ability to resolve conflicting sensory inputs from the visual, vestibular, and somatosensory systems, maintaining postural control becomes more difficult and can result in falls. Overall, there is an increased incidence of vestibular hypofunction and disease of the vestibular system with advancing age. One unwanted consequence is a decrease in dynamic visual acuity, making it difficult for older adults to maintain visual gaze stability on objects as they move in their environment. For example, while walking or driving. Loss of dynamic visual acuity can result in “dizziness” or even motion sensitivity during activities that involve head movement and very few activities do not involve head movement. Therefore, the older adult limits head movement and avoids motions that require faster head motions. For example, they may walk more slowly, with a wider base of support, stop turning their head during gait, lie down in bed more slowly, and limit larger head motions that typically occur with bending over, reaching for objects on high shelves, or turning quickly to look over their shoulder while driving. Although vestibular assessment is a newer area of rehabilitation for many occupational and physical therapists, it is important to recognize signs of avoidance behavior. Lack of head turning, slow gait speed, and/or adapting activities of daily living (ADLs) to avoid head movement are potential signs that should trigger the need a full vestibular evaluation, or a referral to a specialist for a full vestibular assessment. A detailed description of aging and postural control can be found in the textbook Motor Control: Translating Research into Clinical Practice , by Shumway-Cook and Woollacott (2007), which also includes changes in the neurologic and musculoskeletal systems. Sensory changes with a lesser effect on fall risk The previously discussed sensory changes that influence fall risk in older adults are more common, but are not the only sensory modalities affected by the aging process. The following section will explore sensory changes that may influence fall risk to a lesser degree. Hearing Although loss of hearing may be one of the most common complaints about aging of an older adult or their family, hearing loss has a minimal effect on fall risk. Presbycusis, or hearing loss typically due to noise exposure, occurs in the seventh and eighth decades of life, which is later than most other sensory changes. Age-related hearing loss is typically a result of inner ear bone deterioration, sensory neural cell deterioration, and/or
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