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Inferior Field Loss Increases Rate of Falls in Older Adults with Glaucoma

Black, Alex A.*; Wood, Joanne M.; Lovie-Kitchin, Jan E.

doi: 10.1097/OPX.0b013e31822f4d6a
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Purpose. To examine the visual predictors of falls and injurious falls among older adults with glaucoma.

Methods. Prospective falls data were collected for 71 community-dwelling adults with primary open-angle glaucoma (mean age, 73.9 ± 5.7 years) for 1 year using monthly falls diaries. Baseline assessment of central visual function included high-contrast visual acuity and Pelli-Robson contrast sensitivity. Binocular integrated visual fields were derived from monocular Humphrey Field Analyzer plots. Rate ratios (RR) for falls and injurious falls with 95% confidence intervals (CIs) were based on negative binomial regression models.

Results. During the 1-year follow-up, 31 (44%) participants experienced at least one fall and 22 (31%) experienced falls that resulted in an injury. Greater visual impairment was associated with increased falls rate, independent of age and gender. In a multivariate model, more extensive field loss in the inferior region was associated with higher rate of falls (RR, 1.57; 95% CI, 1.06 to 2.32) and falls with injury (RR, 1.80; 95% CI, 1.12 to 2.98), adjusted for all other vision measures and potential confounding factors. Visual acuity, contrast sensitivity, and superior field loss were not associated with the rate of falls; topical beta-blocker use was also not associated with increased falls risk.

Conclusions. Falls are common among older adults with glaucoma and occur more frequently in those with greater visual impairment, particularly in the inferior field region. This finding highlights the importance of the inferior visual field region in falls risk and assists in identifying older adults with glaucoma at risk of future falls, for whom potential interventions should be targeted.

*BAppSc (Optom), PhD

PhD, FAAO

School of Optometry and Institute of Health and Biomedical Innovation, Queensland University of Technology, Queensland, Australia.

Received March 8, 2011; accepted June 27, 2011.

Alex Black School of Optometry; Queensland University of Technology; Victoria Park Road, Kelvin Grove; Queensland 4059; Australia; e-mail: aa.black@qut.edu.au

Falls are a major cause of injury, healthcare utilization, and mortality among older adults.1–3 Approximately one in three adults aged over 65 years experience at least one fall each year, and one-half of these experience multiple falls.1,4,5 The ability to safely navigate through complex environments is highly dependent on visual input, to enable effective path planning and obstacle avoidance,6,7 and visual impairment has been shown to be an important contributing factor for falls and fractures among older adults.4,5,8–12

Binocular visual field loss, regardless of its cause, has been shown to be the leading visual risk factor for falls and fractures among older community-dwelling populations.4,5,8 Glaucoma is the leading cause of irreversible visual field loss among older adults13 and has been associated with higher rates of falls,9,14–16 hip fractures,10 or fall-related hospitalizations17 compared to those with normal vision. In support of this, visual field loss has been linked to slower walking speeds and increased obstacle contacts in mobility studies, both in general older populations18 and among those with glaucomatous visual impairment.19,20 Furthermore, visual field loss among older adults with glaucoma has been linked to greater postural instability,21 which may further increase the risk of falls.22 Other studies, however, have failed to show that glaucoma is associated with increased falls risk.11,23,24 These disparate findings may be attributed to the considerable variations in study designs, sample populations, definitions of falls, and data collection methods in these studies.

Importantly, the pattern of glaucomatous visual field loss differs to that of other eye diseases, because it reflects the distribution of the retinal nerve fibers. Defects are slightly more common in the superior than the inferior hemifield, and individuals with bilateral glaucoma often present with defects in the same hemifield in both eyes.25 This pattern of visual field defects has important functional implications, because the inferior visual field region has been shown to be essential for safe navigation, as demonstrated by mobility studies involving individuals with visual impairment from a range of eye diseases18,26 as well as those involving participants with simulated visual impairment.7 A population study of community-dwelling older adults by Freeman et al.5 assessed the independent contributions of field loss location on prospective falls; however, neither the superior nor inferior field areas were found to be stronger predictors in their multivariate models.

Studies also suggest that topical antiglaucoma medication use, particularly beta-blockers, may increase the likelihood of falls.9,23 These studies, however, are limited as the comparison groups did not use any form of topical antiglaucoma medications and were therefore unlikely to have glaucoma or visual field loss. In contrast, recent research has shown that older adults with glaucoma using topical beta-blockers were no more likely to experience a previous fall, compared with glaucoma patients using prostaglandins.27

The primary objective of this study was to examine which aspects of visual function are most highly associated with falls and injurious falls among community-dwelling older adults with glaucoma, particularly the impact of the location of visual field loss. A secondary objective was to examine whether beta-blocker use was associated with prospective falls in this cohort.

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METHODS

Participants

Seventy-one community-dwelling individuals aged ≥60 years, who were currently being treated for open-angle glaucoma were recruited from the clinical records of the Queensland University of Technology Optometry Clinic, private ophthalmology practices and local members of Glaucoma Australia. Participants were excluded if they had any significant ocular or visual pathway disease leading to visual field loss, other than glaucoma; any form of cataracts graded 3.0 or worse, defined by the Lens Opacities Classification System III28; suffered from Parkinson Disease; history of dizziness or vestibular disease; used a walking aid; or had signs of cognitive impairment (Mini-Mental State Examination score <24 of 30).29 The research followed the tenets of the Declaration of Helsinki, and informed consent was obtained before participant assessment. The study was approved by the Queensland University of Technology Human Research Ethics Committee.

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Demographic Assessment

Data were collected on demographic information (age and gender) and medical information (medical history and current medication use). Self-reported medical and health conditions included arthritis, cancer, diabetes mellitus, hypertension, cardiovascular disease (angina, heart attack), hearing impairment, history of stoke, history of hip fracture, and incontinence.30 A measure of self-rated health was determined by asking participants to rate their own health as either excellent, very good, good, fair, or poor.31 The use of topical antiglaucoma medications was dichotomously coded into either the use of topical medications including beta-blockers, or the use of topical medications other than beta-blockers. Participants reported the number of falls in the 12 months before participation in the study, along with fear of falling status using a single dichotomous question: “Are you worried or afraid of falling, except in a high place?”32 Participants' habitual spectacle correction used for walking was coded as either multifocal (bifocals, trifocals, and progressives) or non-multifocal (no correction, single vision, and contact lenses).

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Visual Function Assessment

Right and left visual acuity was measured with habitual distance refractive correction using a standard Bailey-Lovie high-contrast letter chart at a working distance of 6 m with a chart luminance of 160 cd m−2. Visual acuity was scored as the total number of letters read correctly, converted to logarithm of the minimum angle of resolution units. Right and left letter contrast sensitivities were measured with habitual refractive correction using the Pelli-Robson letter chart at 1 m with a +0.75 DS working distance correction in place,33 chart luminance of 83 cd m−2 and scored as the number of letters correctly identified.34

Visual fields were assessed with a computerized perimeter (Humphrey Field Analyzer; model HFA-II 750; Carl Zeiss Meditec, Dublin, CA). Monocular 24-2 Swedish Interactive Threshold Algorithm-Standard threshold tests were performed by an experienced optometrist. A binocular mean deviation (MD) score was derived by merging the right and left fields to create an integrated visual field (IVF) extending 60° horizontally (IVF-60), based on the more sensitive of the two eyes at each visual field location.35,36 In addition, monocular 81-point, single intensity [24 decibel (dB)] screening strategy tests were performed and merged to create a 96-point IVF extending 120° horizontally (IVF-120), based on the more sensitive of the two visual field locations in each eye, as outlined by Turano et al.18 The IVF-120 was scored as the total number of points missed. Points falling above and below the horizontal midline for the IVFs were used to determine the MD scores (IVF-60) or points missed (IVF-120) for the superior and inferior field areas, respectively.

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Prospective Falls Assessment

Falls were recorded prospectively during the 12-month follow-up using monthly falls diaries.37 Participants were provided with a set of 12 falls diaries to return by mail to the study center at the end of each month. Participants were instructed on how to record the occurrence of any falls and any fall-related injuries on a daily basis in these diaries. In instances where the diaries were not returned promptly, participants were contacted by telephone to ascertain the occurrence of any falls during the corresponding month. In this study, a fall was defined as an “event which results in a person coming to rest inadvertently on the ground or other lower level, and not as a consequence of sustaining a violent blow, loss of consciousness, sudden onset of paralysis or epileptic seizure.”38,39

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Statistical Analysis

Data were analyzed using SPSS (version 16.0; SPSS, Chicago, IL). Analyses were two-tailed, and p values <0.05 were considered statistically significant. Descriptive statistics were calculated for demographic, medical, and visual function data. Negative binomial regression, which is a generalization of the Poisson regression,40,41 was used to examine the association between the number of falls and falls that resulted in an injury and each of the visual function measures, with adjustment for the possible confounding effects of age and gender. Rate ratios (RR) and 95% confidence interval (CI) for falls were calculated per clinically relevant unit reduction or around 10% reduction of the total range to provide clinically meaningful estimates.

As the visual function measures were highly correlated in this glaucoma cohort, the visual function measures were reduced using factor analysis to remove the influence of multicollinearity for multivariate regression modeling.42 Visual acuity, contrast sensitivity, and inferior and superior visual field variables were submitted to principal components analysis using varimax rotation to derive four orthogonal statistically independent factors: acuity, contrast, inferior field, and superior field. Lower factor scores reflected poorer visual function. Multivariate negative binomial regression models were conducted to identify the specific components of vision independently associated with falls and injurious falls, adjusted for all vision factors. Further models also adjusted for a number of potential confounding variables: age, gender, use of multifocal corrections, self-reported co-morbidities, and self-rated health status.

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RESULTS

The mean age of the 71 participants was 73.9 ± 5.7 years (range, 62 to 90 years) and 34 (48%) were female. Participants reported a mean of 2.1 ± 1.4 co-morbidities; the most common conditions were arthritis (51%), hearing impairment (39%), hypertension (39%), heart disease (29%), and history of cancer (27%). Twenty-four (34%) participants reported one or more falls in the previous year and 16 (23%) reported fear of falling. The glaucoma medical history and visual function characteristics of the participants are presented in Table 1. The severity of glaucomatous visual impairment based on the extent of visual field loss, ranged from early to advanced, with IVF-60 MD scores of −4.10 ± 6.28 dB (range, −28.23 to 1.59) and IVF-120 points missed 32 ± 21 (range, 6 to 96).

TABLE 1

TABLE 1

At follow-up, 31 (44%) participants reported one or more falls; 17 (24%) fell only once, whereas 14 (20%) fell two or more times (up to a maximum of nine falls). Twenty-two (31%) participants reported one or more injurious falls, all of which resulted in soft tissue injuries (bruises, abrasions, and sprains of the upper and lower limb). No serious fall-related injuries were reported.

The association between the vision measures and falls and injurious falls, adjusted for age and gender, are presented in Table 2. Greater reduction in visual function across all the vision measures was associated with an increased rate of falls. The better-eye measures of visual acuity and contrast sensitivity were better predictors of falls than the worse-eye measures. For both of the visual field measures, greater binocular inferior visual field loss was the strongest predictor of falls. Each 5 dB reduction in the inferior IVF-60 at baseline was associated with a 56% higher rate of falls during the 12-month follow-up (RR, 1.56; 95% CI, 1.22 to 1.99), whereas 10 points missed in the inferior IVF-120 at baseline was associated with a 62% higher rate of falls during the 12-month follow-up (RR, 1.62; 95% CI, 1.23 to 2.14). The inferior visual field measures were the only visual function measures significantly associated with injurious falls. Participants using topical beta-blocker medications had a lower rate of falls (RR, 0.76; 95% CI, 0.39 to 1.48) and injurious falls (RR, 0.57; 95% CI, 0.24 to 1.37) than those not using these medications, although these estimates did not reach significance.

TABLE 2

TABLE 2

The regression models were also examined to specifically explore whether one visual field strategy was superior to the other in terms of predicting falls and injurious falls outcomes. There were no significant differences in goodness of fit between models which included the full-field IVF-60 or full-field IVF-120, or between models which included the inferior IVF-60 or inferior IVF-120 (differences in Akaike Information criterion values <2; Vuong Non-Nested Test, p > 0.05).43,44

The loadings of the vision variables used to generate the four vision factors are shown in Table 3. In the multivariate models including all vision factors (Table 4), the inferior field was the only vision factor significantly associated with falls or injurious falls. This association remained significant following adjustment for age, gender, use of multifocal spectacle corrections, number of self-reported co-morbidities, and self-rated health status. In the fully-adjusted model, each unit reduction in the inferior field factor at baseline was associated with a 57% higher rate of falls (RR, 1.57; 95% CI, 1.06 to 2.32) and an 82% higher rate of injurious falls (RR, 1.80; 95% CI, 1.12 to 2.98) during the 12-month follow-up. The acuity, contrast, and superior field factors were not associated with the rate of falls or injurious falls in any of the multivariate models.

TABLE 3

TABLE 3

TABLE 4

TABLE 4

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DISCUSSION

This study of community-dwelling older adults with glaucoma demonstrated that greater visual impairment, particularly binocular inferior visual field loss, was associated with an increased risk of prospective falls and injurious falls. This finding is consistent with previous research among population-based cohorts4,5 and is the first to report a significant link between inferior visual field loss and falls and injurious falls exclusively in a cohort of older adults with glaucoma.

The finding that ∼44% of the glaucoma participants reported one or more falls and over 20% reported two or more falls during the 12-month follow-up is consistent with that of previous population studies, although it is difficult to make direct comparisons because of variations in cohort characteristics, falls outcomes, and study designs. Prospective community-based studies report annual falls rates of the order of 30%, and multiple falls of the order of 16%4,5; however, there have been no previous prospective falls studies of individuals with glaucoma. In retrospective case-control studies, around 35 to 38% of participants with glaucoma reported one or more falls in the previous year16,20; and ∼10% of participants attending a glaucoma clinic, of whom 70% had a positive diagnosis of glaucoma, reported an injurious fall in the previous 12 months that required medical attention.23

Recent studies have reported significant associations between visual field loss and prospective falls risk,4,5 which is consistent with our findings. Freeman et al.5 reported that every 10 point loss of binocular visual field (identical to the IVF-120 in the present study) was associated with an 8% higher odds of falling after adjustment for potential confounding factors in their population-based study. Coleman et al.4 reported that the risk of falling among older women was 50% greater in those with severe visual field loss, defined as 20 or more points missed in a binocular visual field from a 76-point field screening strategy, compared with those with no visual field loss. In this study, every 10 points missed on IVF-120 at baseline was associated with a 25% higher rate of falls, whereas every 5 dB reduction in IVF-60 at baseline was associated with a 47% higher rate of falls. Comparisons between studies are difficult, however, because of differences in the visual field assessments, fall outcomes, statistical analyses, and study populations.

The inferior field region was shown to be an important predictor of prospective falls in this study, more so than superior field loss. This is in general agreement with Coleman et al.4 who reported that the odds of falling among older women with severe inferior visual field loss, when compared with no inferior loss, were 91% higher, whereas the odds of falling among those with severe superior visual field loss, when compared with no superior visual field loss, were only 74% higher. The risk of falls appeared higher among those with inferior field loss, although Coleman et al.4 did not statistically assess the independent contributions of these field regions to the risk of falls. Freeman et al.5 did examine the independent contributions of field loss location on prospective falls; however, neither the superior nor inferior field areas were found to be stronger predictors in their multivariate models. Importantly, Freeman et al.5 excluded the central 20° radius areas in their calculation of inferior and superior field loss in their cohort with a broad range of eye diseases, although we included this region in our analysis.

Our findings highlight the importance of the inferior visual field in negotiating real-world complex environments. When walking, people have been shown to fixate approximately two steps ahead,46 and the inferior visual field contributes a major proportion of visual information used to guide lower limb movements, foot placement, and obstacle detection.7 This is supported by studies, which report that greater loss in the central and inferior visual field areas impact negatively on mobility performance among adults with visual impairment.18,26

An interesting question, that is relevant to clinical practice, is whether a particular visual field assessment strategy better predicts falls outcomes in this population. However, our findings failed to provide any evidence that one field strategy was superior to the other in terms of predicting these outcomes. We suspect that this was due to the high correlations between the different field tests included in this study (r > −0.90). These findings indicates that routinely measured monocular 24-2 threshold field tests used for glaucoma assessment and monitoring, when considered as an integrated binocular field, are as good at identifying individuals who may be at risk of falls as more peripheral screening field tests.

The use of topical beta-blockers was not found to be associated with prospective falls. Our findings are consistent with a recent retrospective falls study, which found that older adults with glaucoma using topical beta-blockers were no more likely to report a fall in the previous year than those using topical prostaglandins,27 and no significant association between oral beta-blocker use and falls was shown in previous studies.47–49 Although some studies have found an association between topical beta-blocker use and falls,9,23 they failed to consider the confounding effect of vision loss in their analyses, because control participants did not use any glaucoma medications, thus were unlikely to have glaucomatous visual impairment. Topical beta-blockers remain a common treatment modality for glaucoma, and our findings suggest that their use poses no additional risk for falls among older adults compared with other topical glaucoma medications.

A strength of this study includes the comprehensive assessment of visual function using standard tests, particularly binocular IVFs, in a well-defined cohort of older adults with glaucoma. In addition, falls were collected prospectively, which enables the causal relationship between vision loss and falls to be examined and is the gold-standard method for accurate falls data.37 The study, however, was limited by its relatively small sample size, even though significant and clinically meaningful findings were demonstrated. We cannot exclude the possibility that there was some recruitment bias toward higher functioning participants who attended the research visits, which may have resulted in conservative estimates of the true association between visual impairment and falls; it is possible that the impact of glaucomatous visual impairment on falls is even greater in frailer, less independent populations.

The prevention of falls among older adults with glaucoma would benefit from increased awareness of the links between visual field loss and falls among patients and eye care practitioners. Although glaucomatous visual impairment is irreversible, there may be other options that could assist in reducing falls in this population. Possible interventions include promoting behavioral change to reduce risk-taking behaviors or modifying other non-vision risk factors for falls, such as physical function or environmental factors.

In conclusion, the findings of this study and that of other recent studies4,5,8 highlight the importance of screening for visual field loss as an integral component in falls risk assessments. The binocular inferior visual field region was an independent predictor of falls and injurious falls, whereas the remaining components of vision did not play a significant role in predicting these outcomes. The significance of this work is that the inferior visual field area is an overlooked and potentially important risk factor for falls among older adults. Given the serious consequences of falls, the significant association between visual field loss and falls highlights the need to target potential interventions to maintain the independence, health, and well-being of older adults with glaucoma.

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ACKNOWLEDGMENTS

We thank Professor Beth Newman for her valuable assistance with study design and statistical advice and all of those people who participated in the study.

This project was supported by Queensland University of Technology and the Institute of Health and Biomedical Innovation. Also supported by an Australian Postgraduate Award and a Queensland University of Technology Vice-Chancellor Scholarship (to AAB).

Alex Black

School of Optometry

Queensland University of Technology

Victoria Park Road, Kelvin Grove

Queensland 4059

Australia

e-mail: aa.black@qut.edu.au

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    Keywords:

    glaucoma; visual field; visual impairment; falls; injury

    © 2011 American Academy of Optometry