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1 From the Department of Ophthalmology, the University of Sydney; and the 2 National Centre for Epidemiology and Population Health, Australian National University, Canberra.
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Abstract |
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METHODS. The Blue Mountains Eye Study examined 3654 residents aged 
49 years
(82.4% response) in an area west of Sydney, Australia. Presenting and
best-corrected visual acuity (VA) were measured before and after
refraction using a LogMAR chart. During a face-to-face interview,
self-rated health was assessed by asking: "For someone of your age,
how would you rate your overall health?: excellent, good, fair, or
poor." Information about demography, socioeconomic status, need for
assistance in daily living activities, medical history, and health risk
behaviors was also collected. Logistic regression analyses were
performed after dichotomizing self-rated health as poor or fair (low)
versus good or excellent.
RESULTS. Among persons without visual impairment (defined from best-corrected VA in the better eye), 24.5% rated their health as either poor or fair, compared with 35.5% and 48.8% of persons with mild or moderate-to-severe visual impairment, respectively. In multivariate logistic regression models that included 17 other related factors, reduced vision was statistically significantly associated with lower self-rated health in persons aged <80 years. For each one-line (5 letter) reduction in best-corrected VA, there was 20% increased likelihood of low self-rated health, after adjustment for other factors found associated with self-rated health (multivariate-adjusted odds ratio 1.2, 95% confidence interval 1.1–1.3). In persons aged 80 years or older, reduced vision had no impact on global health rating.
CONCLUSIONS. Decreased vision was found to have an independent impact on global health ranking by persons younger than age 80 years, but not by older persons in this population. Taking into account many other factors affecting perceived health, people younger than age 80 years who see well are also more likely to say that they feel well!
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Introduction |
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The factors that influence a person to rank his/her global health at a particular level are still not well understood. People with different ages, gender, race, and educational backgrounds were reported to rate their health statuses differently.4 5 6 Among older people, physical health or presence of chronic disease appears to influence the rating more than among younger adults.5 Components included in self-rating of global health appear to involve more than physical health and function. The rating is likely to be a multidimensional conceptual measure4 7 8 that includes activity scores and social interaction,9 contentment with life, and problems with mobility.10
Many previous studies,11 12 13 14 most recently the SEE Study,15 have documented an association between visual impairment and a decreased ability to perform daily living activities by elderly persons. Carabellese et al. have also documented an association between visual impairment and quality of life, particularly for depression and reduced social interaction.16 These findings have been confirmed in studies of specific eye diseases, such as macular degeneration,17 glaucoma,18 19 and cataract.20
However, only a few studies have reported the relationship between sensory impairment and self-rated health,8 10 21 with these studies reporting different findings. Wolinsky et al.8 assessed the correlation among seven health measures in a weighted sample of 401 urban subjects aged 65 years or older from St. Louis and found that sensory functions and perceived health status were strongly correlated, with a correlation coefficient of 0.42. The Swedish Albertina Project reported that although eyesight and hearing problems were common in the study population of 706 persons aged 75 years or older, these problems did not affect perceived health to any large extent.10 Gresset et al.21 also reported no significant correlation between visual acuity (VA) of the better eye and perception of general health in a validation study of a French version of the Visual Functioning Index (VF-14).
We could not identify any detailed studies reporting the relationship between VA and self-rated health. The Blue Mountains Eye Study provided an opportunity to examine this relationship because a standardized question on self-rated health was included as part of the structured interview. The purpose of the current article is to assess the relationship between reduced best-corrected or presenting VA and a low self-rating of global health, after taking into account a wide range of factors that could potentially influence this measure.
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Methods |
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Global self-rated health status was assessed by asking a question with four possible answers during a face-to-face interview: For someone of your age, how would you rate your overall health; would you say it is excellent, good, fair, or poor?
Social-demographic measures were assessed and defined dichotomously.
Average or high educational qualification was defined in persons with a
trade certificate or higher qualification.23
Subjects were
asked whether they owned or rented their home, and whether they lived
alone, with a spouse, or with another person. A past history of angina,
acute myocardial infarct (heart disease), stroke, hypertension,
diabetes, cancer, arthritis, asthma, gout, or thyroid conditions was
recorded. The number of coexisting chronic diseases, rather than each
individual disease, was used as an alternative independent variable in
the model. Participants were also asked whether they had a hearing
problem and whether they had been admitted to a hospital in the last 12
months. Smoking status and alcohol consumption were assessed. People
who were current smokers were compared to ex- and never-smokers. Heavy
drinkers (average consumption 4 drinks per day) were compared with
persons who reported none, light, or moderate alcohol consumption.
Walking exercise during the previous 2 weeks was assessed.
Limitation in performing daily activities was assessed by asking questions about whether the participants felt able to go out alone or regularly used any community support services, including "Meals-on-Wheels," Home Care, or regular home visits by a community nurse.24 We assumed some limitation in performing daily living activities in persons who regularly used any community support services. Difficulty in walking or use of a cane, walker, or wheelchair at the clinic visit was assessed by one examiner and categorized as "difficulty in walking."
During the examination, presenting VA was measured while subjects were wearing current distance glasses correction, using a logMAR chart. Best-corrected VA was then measured after a subjective refraction, as described previously.25 For each eye, VA was recorded as the number of letters read correctly: from 0 (less than 20/200) to 70 (20/10) letters. Visual impairment levels were defined using either presenting or best-corrected VA in the better eye, with the same criteria as in the Beaver Dam Eye Study26 : no visual impairment, Snellen equivalent better than 20/40 (41–70 letters read correctly); mild visual impairment, 20/40 to 20/60 (26–40 letters correct); moderate visual impairment, 20/80 to 20/160 (6 to 25 letters correct); and severe visual impairment, 20/200 or worse (0–5 letters correct).
Statistical Analysis System (version 6.12; SAS Institute, Cary, NC) was used for statistical analyses, included the chi-square statistic and logistic regression. Self-rated health was dichotomized into two levels: fair or poor versus excellent or good, as the dependent variable. Associations between the dependent variable and each independent variable were assessed initially using the chi-square statistic and in age-adjusted logistic regression models.
Presenting and best-corrected VAs (number of letters read correctly) were treated as continuous independent variables. A multivariate logistic regression model was constructed using a stepwise procedure to include all variables found to be significantly associated with fair or poor (low) self-rated health. All biologically plausible interactions between covariables were checked during modeling. Only age and best-corrected VA had a significant interaction in the final multivariate model. To further explore this interaction, analyses stratified by age were then conducted. Different levels of projected VA reduction were assessed in the model for persons younger than 80 years. Odds ratios (OR), 95% confidence intervals (CI), adjusted R2, and goodness-of-fit statistics from the multivariate model are presented.
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Results |
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A wide range of variables (n = 19) was found to be significantly associated with low self-rated health including demographic or socioeconomic variables, physical limitations, chronic diseases, health risk behaviors, and sensory impairment, which are shown in Table 2 . The multivariate logistic regression model included all these variables. An increased likelihood of low self-rated health was significantly associated in the model with reduced VA. This association was consistent and relatively stable as variables were added to the model. For each one-line (5-letter) reduction in best-corrected VA, the OR for low self-rated health was 2.1 (CI 1.5–2.9) in the model containing age, VA, and an interaction term for the two variables. The corresponding OR in the final multivariate model, which contained 17 additional variables, was 1.9 (range, 1.2–3.0), as shown in Table 2 . Replacing each individual chronic disease by a set of dummy variables representing number of coexisting chronic diseases in this model did not alter the impact of reduced vision on low self-rated health (OR, 1.8; CI 1.2–2.6; results not shown).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The Blue Mountains Eye Study was not specifically designed to answer the study questions in this report, so that our findings have limitations. The assessment of self-rated health was based on a single question, and information on a majority but not all possible confounders was collected and available for analysis. However, with the information collected, we were able to provide some insight into the nature of self-rated health and give a preliminary answer to the question above. If measurement error occurred in classification of the outcome (self-rated health), it would only lead to an underestimation of the association found.
Our findings demonstrate a significant, but relatively modest, relationship between reduced VA and a low self-ranking of global health in people aged 49 to 79 years. Although few studies have examined this particular association, our report builds on findings from a number of recent studies, as mentioned earlier.
We found a significant interaction between age and best-corrected VA in the multivariate model, suggesting that the relationship was modified by age. After age stratification (<80/80 + years), we found that the association was only present for persons younger than age 80 years. Previous self-rated health studies have consistently found that age modifies the association between disabilities and self-rated health.5 29 30 31 32 33 Older elderly persons may be more likely than younger elderly persons to rate their health as excellent or very good at a given level of chronic disease or functional disability.31 32 Our findings confirmed this phenomenon. After age 80 years, only half the variables including hospital admissions in the past 12 months, walking difficulty, histories of angina, asthma, or hypertension, and health risk behavior variables continued to exert a significant impact on self-rated health. It is possible that when people get to this age, they may accept reduced vision as an expected part of normal aging, which then has no further impact on the perception of their global health. Increasing age had an inverse effect on low self-rated health among study participants aged less than 80 years. This age trend has been reported in many studies of self-rated health.5 30 31 33 34 35 36 37 Why does the perception of health apparently change for the better or at least not decline for many people as they grow older? Idler31 summarized theories put forward to explain this phenomenon in terms of a reference group, birth cohort differences, and survivorship. Survivorship could be the most likely explanation, as suggested by Idler31 : "Lifelong health optimists come to dominate the composition of their cohorts as they reach their eighties and beyond ... . "
A person’s perception of his or her general health appears to be a multidimensional conceptual measure, involving not only physical health and functions but also mental health and psychosocial factors.7 8 Our study was not able to cover all the factors that determine a low health self-rating, not only because many variables and their interactions are unknown but also because we did not include mental health or psychosocial questions. However, the study has covered a wide range of variables, including socioeconomic status, many chronic diseases, health risk behaviors, and sensory function impairments. After controlling for these variables, reduced vision was found to provide a modest, significant, and independent contribution to the likelihood that a person aged less than 80 years would rank his or her health as low. This finding is unlikely to have occurred by chance.
We used a stepwise procedure to construct the multivariate model for low self-rated health. As each variable was added to the model, estimates of association for variables already in the model did not change substantially. This indicated that each variable in the model had an independent impact on the ranking of low global health. If unmeasured variables in our study such as those pertaining to mental health or psychosocial factors, were added, they could also be independent or could confound or interact with other variables in the model. Further studies are therefore needed.
Previous studies have suggested that the number of illness episodes is strongly related to self-rating of health.38 In the multivariate models, we also used number of chronic diseases, instead of each individual disease, as an alternative approach to assess the relationship between reduced vision and low self-rated health. This measure could be analogous to a "mean co-morbidity score" used in a previous report of the functional impact of visual impairment.39 Our findings confirmed a gradient between number of chronic diseases and likelihood of low self-rated health. However, we showed that the modest contribution of reduced vision to low self-rated health was independent of the type and number of other chronic diseases present in an individual.
Our findings are not surprising, given evidence from past studies. Self-rated health is highly correlated with objective health status,33 disability,11 14 and functional limitations.6 Visual impairment in older people has been associated with a decreased ability to perform daily living activities11 12 13 14 15 as well as leading to an increased reliance on community support services and on help from family members and friends.24 Contentment and perceived health have also been found to be highly correlated in persons aged 75 years or older.10 Visual impairment has been shown to be associated with an increased risk of depression and reduced social interaction.16 A study assessing factors associated with the wish to die in elderly people found a number of factors, independent of depression.40 Visual impairment was a strong risk factor, along with hearing impairment, poor self-rated health, being in residential care, and other factors.
Our report also demonstrated that reduced presenting VA (wearing current glasses, if worn) paralleled, but at a slightly lower magnitude, the impact of reduced best-corrected VA (after a standardized subjective refraction) in its association with a low health self-rating. This finding is similar to the effect we have previously reported from visual impairment on the use of community support services.24 These findings suggest that presenting VA may be a reasonable measure of impaired vision, but that because of misclassification, it could underestimate the association between low self-rated health and pathologically impaired vision.
In summary, our study examined whether reduced vision and low self-rated health are related, in a representative older population, after adjusting for a wide range of factors likely to affect this measure. We found that reduced vision, defined from measurements of either best-corrected or presenting VA, had a modest yet independent impact on global health ranking in people aged younger than 80 years in this population. For each one-line decrease in best-corrected vision, there was a 20% increased likelihood of low self-rated health. Taking into account many other factors affecting perceived health, people younger than age 80 years who see well are also more likely to say that they feel well!
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Footnotes |
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Submitted for publication January 27, 1999; revised April 23 and July 23, 1999; accepted August 17, 1999.
Commercial relationships policy: N.
Corresponding author: Paul Mitchell, Department of Ophthalmology, the University of Sydney, Eye Clinic, Westmead Hospital, Westmead, NSW, Australia, 2145. paulmi{at}westmed.wh.su.edu.au
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