In 1864, Franciscus Cornelis Donders was the first researcher to examine age-related changes in vision. Since then, many researchers have found age-related changes in visual acuity, despite varying assessment methods. In general, the findings of large cross-sectional and longitudinal studies show that visual acuity improves slightly from childhood to 20 years of age, remains fairly constant up to 50 years and then steadily declines (Gittings and Fozard, 1986; Pitts, 1982).

Other research has also documented age-related declines in contrast sensitivity, glare sensitivity, dark adaption, accommodation and depth perception, and that these changes are especially evident beyond the fourth decade (Pitts, 1982).

Impaired vision can have substantial adverse effects on an older person's ability to read, enjoy recreational pastimes and undertake activities of daily living. As outlined below, impaired vision also directly affects balance and predisposes older people to falls.

In addition to allowing us to detect hazards in the environment, vision plays a direct and important role in stabilizing balance by providing the nervous system with continually updated information regarding the position and movements of body segments in relation to each other and the environment. When people stand with their eyes closed, postural sway increases between 20% and 70% (Magnusson et al., 1990; Paulus et al., 1984). It has also been found that moving visual fields can induce a powerful sense of self-motion and misleading visual cues induce significant increases in sway (Lee and Lishman, 1975).

Impaired vision has been associated with postural instability in older people in several studies. Lichtenstein et al. (1988) found that poor near-visual acuity was associated with increased sway, and Manchester et al. (1989) found that stability in older adults was significantly decreased when peripheral vision was occluded. Complementary findings were reported by Turano et al. (1994), who found that good contrast sensitivity assisted in stabilizing balance in a sample of 185 older people.

In a series of studies, we have found that visual acuity and contrast sensitivity are significant predictors of sway when older subjects stand on a compliant foam rubber surface (Lord et al., 1991; Lord and Menz, 2000). It has also been reported that people with age-related maculopathy have increased sway in this condition (Elliott et al., 1995). When standing on a foam mat, proprioceptive input from the feet and ankles is reduced, and subjects are compelled to rely more on other sensory and motor systems to maintain stability.

In our most recent study, we found that the best predictors of sway on the compliant surface were contrast sensitivity, stereopsis (the ability to converge the slightly disparate retinal images from the two eyes to perceive depth) and quadriceps strength (Lord and Menz, 2000). The inclusion of both contrast sensitivity and stereopsis in the predictive model suggests that the ability to detect relevant visual stimuli and perceive spatial relationships are both important for the control of balance. Complementary visual abilities such as these appear to contribute to steady stance under more challenging conditions by detecting the larger movements of the body relative to its surroundings.

Impaired balance in older people manifests as falls and fall-related injuries. Approximately one-third of older people living in the community fall at least once a year, with many suffering multiple falls (Campbell et al., 1989; Tinetti et al., 1988). Falls are the leading cause of injury-related death and hospitalization in people age 75 years and older (Baker and Harvey, 1985). Falls can also result in disability, restriction of activity and fear of falling, all of which reduce quality of life and independence. Furthermore, falls can contribute to the placement of an older person into institutional care (Lord et al., 2001).

There are a number of complementary tests of visual function relevant to risk of falling in older people. These include tests of standard high-contrast visual acuity (letter charts), low-contrast visual acuity (letter charts with gray rather than black letters), visual contrast sensitivity, depth perception, stereopsis and visual field size.

Recent research has shown that while standard measures of visual functioning such as visual acuity and visual field size are fair predictors of falls, other tests that address more closely the visual functions required for maintaining balance and detecting hazards are superior (Ivers et al., 1998; Lord and Dayhew, 2001; Nevitt et al., 1989). For example, we have recently found that of nine measures of vision, impaired depth perception was the strongest risk factor for multiple falls in community-dwelling older people (Lord and Dayhew, 2001). Furthermore, subjects with good vision in both eyes had the lowest rate of falls, whereas subjects with good vision in one eye but only moderate or poor vision in the other had elevated falling rates that were equivalent to those of patients with moderate or poor vision in both eyes. This suggests that the ability to judge distances accurately and perceive spatial relationships is important for negotiating and avoiding obstacles and hazards in the environment.

An ability to detect objects is also important and is indirectly assessed with tests of edge contrast sensitivity. These tests measure a person's ability to detect edges under low-contrast conditions and may reflect ability to detect ground-level hazards. Thus, a loss of edge contrast sensitivity may predispose older people to trip over obstacles within the home and over hazards outdoors, such as steps, curbs, and pavement cracks and misalignments.

Presbyopia (the reduced ability to focus on close objects) affects all people age 50 and older. To correct this condition, older people are prescribed either separate single-lens glasses for distant and near vision or, for convenience, a single pair of multifocal (bifocal, trifocal or progressive lens) glasses. Multifocal glasses have definite benefits for specific tasks that require changes in focal length, including everyday activities such as driving, shopping and cooking.

However, multifocal glasses also have disadvantages because the lower lenses blur floor-level objects at critical distances for detecting environmental hazards (Lord et al., 2002). This factor may represent a significant problem for older people, as they are more likely to fall over a hazardous object.

In a prospective cohort study of 156 people ages 63 to 90, we found that 87 (56%) were regular wearers of multifocal glasses (Lord et al., 2002). These study participants performed significantly worse in both distant depth perception and distant edge contrast sensitivity tests when viewing test stimuli through the lower segments of their glasses. These visual impairments appeared to have significant practical implications because the regular wearers of multifocal glasses were more than twice as likely to suffer falls when outside their homes or when negotiating stairs in a one-year follow-up period compared with those who did not wear multifocal glasses.

Simple intervention strategies such as regular eye examinations, cataract surgery, prescription of appropriate glasses, the use of single-lens distance glasses in lieu of multifocal glasses when in higher-risk situations (e.g., when negotiating stairs, walking outside, getting on or off public transport, or stepping into and out of a car), and the removal of tripping hazards in the home and public places have the potential to prevent falls in older people. As poor vision in one eye only elevates the risk of both falls (Lord and Dayhew, 2001) and fall-related fractures (Felson et al., 1989), strategies to maximize vision in both eyes may also be particularly beneficial in preventing falls.

Dr. Lord is principal research fellow at the Prince of Wales Medical Research Institute in Sydney, Australia. His research interests include the identification of risk factors for falls in older people and the design and evaluation of fall prevention strategies.

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Vision, Balance and Falls in the Elderly