September 2011
Volume 52, Issue 10
Free
Clinical and Epidemiologic Research  |   September 2011
Literacy Is an Independent Risk Factor for Vision Impairment and Poor Visual Functioning
Author Affiliations & Notes
  • Yingfeng Zheng
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore;
    the State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • Ecosse L. Lamoureux
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore;
    the Centre for Eye Research Australia, University of Melbourne, Victoria, Australia;
  • Peggy Pei-Chia Chiang
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore;
  • Ching-Yu Cheng
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore;
    the Departments of Ophthalmology and
    Epidemiology and Public Health, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; and
  • Ainur Rahman Anuar
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore;
    the Department of Ophthalmology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
  • Seang-Mei Saw
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore;
    the Departments of Ophthalmology and
    Epidemiology and Public Health, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; and
  • Tin Aung
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore;
    the Departments of Ophthalmology and
  • Tien Yin Wong
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore;
    the Centre for Eye Research Australia, University of Melbourne, Victoria, Australia;
    the Departments of Ophthalmology and
    Epidemiology and Public Health, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; and
  • Corresponding author: Tien Y. Wong, Singapore Eye Research Institute, 11 Third Hospital Ave, #05-00, Singapore 168751; ophwty@nus.edu.sg
Investigative Ophthalmology & Visual Science September 2011, Vol.52, 7634-7639. doi:10.1167/iovs.11-7725
  • Views
  • PDF
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      Yingfeng Zheng, Ecosse L. Lamoureux, Peggy Pei-Chia Chiang, Ching-Yu Cheng, Ainur Rahman Anuar, Seang-Mei Saw, Tin Aung, Tien Yin Wong; Literacy Is an Independent Risk Factor for Vision Impairment and Poor Visual Functioning. Invest. Ophthalmol. Vis. Sci. 2011;52(10):7634-7639. doi: 10.1167/iovs.11-7725.

      Download citation file:


      © ARVO (1962-2015); The Authors (2016-present)

      ×
  • Supplements
Abstract

Purpose.: People with limited literacy are at increased risks of chronic systemic conditions. The authors therefore investigated the independent contribution of limited literacy on visual impairment and visual function in a large eye survey in Singapore.

Methods.: The authors undertook a population-based, cross-sectional study of Asian Malays (≥40 years old). Visual impairment was defined as logMAR (logarithm of minimal angle of resolution) visual acuity > 0.30 in the better-seeing eye. Information regarding reading and writing literacy levels and other independent variables, including sociodemographic measures (e.g., education, income), were obtained from a standardized interview. Visual functioning was assessed using a modified and validated version of the Vision-Specific Functioning Scale using Rasch analysis.

Results.: Of the 3280 participants, 553 (16.9%) had inadequate reading literacy and 688 (21.0%) had inadequate writing literacy. In multivariate analysis, persons with inadequate reading literacy were more likely to have presenting visual impairment (odds ratio [OR] = 2.66; 95% confidence interval [CI] = 1.91 to 3.72; P < 0.001), best-corrected visual impairment (OR = 2.59; 95% CI = 1.70 to 3.96; P < 0.001), and poorer visual functioning (β coefficient = 0.58; 95% CI = 1.57 to 3.02; P < 0.001), even controlling for education, income, and other patients' characteristics. Similar associations were found for inadequate writing literacy.

Conclusions.: Inadequate literacy is independently associated with visual impairment and poorer visual functioning. Interventions that address literacy may help to reduce socioeconomic disparities in visual impairment.

Literacy is traditionally defined as the ability to understand verbal and written materials. People with inadequate literacy have difficulties understanding medical information and adhering to treatment regimens. 1 3 Previous studies have consistently shown that people with inadequate literacy are more likely to have chronic medical conditions (e.g., diabetes and heart disease), 4,5 more frequent hospital admissions, 6 and increased risk of mortality 7 compared with their literate counterparts. Although poor people, the uninsured, the unemployed, and ethnic minorities are common among people with low literacy, the latter has been consistently identified as an independent risk factor for poorer health outcomes, independent of measures of education, income, insurance, employment status, and ethnicity. 8,9  
Although there is a considerable literature on the link between inadequate literacy and systemic health, 1 8 there is limited information and understanding about the influence of literacy on visual impairment, one of the world's major public health problems. Given that literacy is a potentially modifiable factor, isolating the independent contribution of inadequate literacy on visual outcomes may have broad strategic implications for the control of avoidable visual impairment. For example, improving literacy in the community may be a more achievable outcome for public health strategies than increasing income or employment opportunities for a certain population. 9  
In addition to being a potential indicator of visual impairment, literacy may also have an impact on various aspects of health-related quality of life (QoL). 10,11 The Vision-Specific Functioning Scale, such as the visual function-14 (VF-14) questionnaire, is a widely used tool to quantify patient-reported functioning and how poor vision limits vision-dependent daily activities. 12 Considering that visual impairment explains only 30–40% of the variance in vision-specific QoL, 13 it would be interesting to investigate the impact of illiteracy on vision-specific functioning. 
In this study, we therefore assessed the visual impacts of literacy in an ethnic Malay population (≥40 years old) living in Singapore. Our aim was to estimate the influence of inadequate literacy on visual impairment and on visual function measured by the VF-9 questionnaire (a modified VF-14 questionnaire). 
Methods
Study Population
The Singapore Malay Eye Study (SiMES) was a population-based cross-sectional study of Singaporean Malays (≥40 years old). The methodology details have been published previously. 14,15 In brief, the Ministry of Home Affairs provided initial computer-generated lists of ethnic Malays residing in 15 postal districts in southwest Singapore. Of the 4168 eligible subjects from the sampling frame, 3280 (78.7%) participated. The study adhered to the Declaration of Helsinki and ethics approvals were obtained from the Singapore Eye Research Institute Institutional Review Board. 
Visual Acuity Testing and Definition of Visual Impairment
The examination included visual acuity (VA) testing and a detailed clinical slit-lamp examination. 15 VA was measured using a logarithm of the minimum angle of resolution (logMAR) number chart (Lighthouse International, New York, NY) at a distance of 4 m. If no numbers were read at 4 m, the participant was moved to 3, 2, or 1 m, consecutively. If no numbers were identified on the chart at 1 m, VA was assessed as Counting Fingers, Hand Movements, Perception of Light, or No Perception of Light. Refraction was corrected by certified optometrists and the best-corrected VA was obtained. Bilateral visual impairment was defined as VA worse than 20/40 (logMAR > 0.30) in the better-seeing eye. 
Vision-Specific Function Assessment
Vision-specific function was assessed using the interviewer-administered VF-11, a modified version of the VF-14. We have previously performed Rasch analysis (RUMM2020 Windows Program for Rasch Unidimensional Measurement Model; RUMM Laboratory, Perth, Australia, 2003) to assess the validity and reliability of VF-11. 16 20 Rasch analysis assumes that the probability that a participant's response to an item depends on both that person's ability and item difficulty. The higher the probability of a participant's response, the larger the difference between the item's required ability and the participant's visual ability. Two items in the VF-11, daytime driving and night-time driving, were removed from the analysis due to misfit. 16 The modified VF-9 had an acceptable model fit and sufficient ability to discriminate people with different levels of visual functioning. Based on Rasch analysis, our group has previously validated the VF-9 in this Malay population by showing that VF-9 is free of differential item functioning (DIF) in terms of age, sex, type of eye disease, degree of visual impairment, comorbidity, and culture. 16 VF-9 has also been demonstrated as a valid unidimensional scale to measure visual functioning in patients with major eye disease (e.g., cataract, diabetic retinopathy, refractive errors) and visual impairment. 16 20 Therefore the VF-9 questionnaire was used in the current analysis. The overall functioning score is expressed in log of the odds units, or logits, positioned along a hierarchical scale. The scale is linear and a higher overall score represents a better visual functioning and less difficulty with items. We also assessed literacy-related DIF for the VF-9 questionnaire. A DIF-free scale should behave similarly independent of age, sex, or other characteristics. Literacy-related DIF occurs if examinees from different literacy groups, but with the same level of ability, have different probabilities of answering the item correctly. There are two types of DIF: uniform and nonuniform. The DIF effect is uniform if the interference associated with group membership is independent of the trait level (uniform DIF is analogous to a confounding relationship); the DIF effect is nonuniform if the interference associated with group membership varies across the trait level (nonuniform DIF is analogous to effect modification). 
Literacy Assessment and Other Measurements
A detailed interviewer-administered questionnaire was used to collect questions on literacy and relevant demographic and socioeconomic information. Literacy level was evaluated by asking “Can you read?” and “Can you write?” A negative response to the first question classified the participants as having inadequate reading literacy and a negative response to the second question, as having inadequate writing literacy. After these questions, the interviewer reminded the participants that these questions were designed to assess the literacy level rather than their visual conditions. As such, any participant who indicated that difficulty in reading or writing was due to a visual condition was classified as literate. 
Other collected information included age, sex, marital status (married; never married; separate or divorced; widowed), smoking history (past or never; current), education (polytechnic/University; secondary education; primary education; no formal education), language of interview (Malays; English; others), occupation (service work; professional/office work; factory work; homemaking; unemployed/others), income (earning > Singapore dollar [SGD] 1000 per month; retirement income; earning <SGD 1000), and current housing status (5-room flat/private house; 3-/4-room flat; 1-/2-room flat). 
Height was measured with a wall-mounted tape and weight with a digital scale (SECA, model 782 2321009; Vogel & Halke GmbH, Hamburg, Germany). The body-mass index (BMI) was calculated by dividing weight (in kg) by the square of height (in m). Diabetes mellitus was defined as the nonfasting blood glucose level ≥11.1 mM or self-reported physician-diagnosed diabetes or use of diabetic medications. 
Statistical Analysis
Logistic regression was performed to calculate the odds ratio (OR) and the 95% confidence interval (CI) for the association between potential risk factors (e.g., age, sex, language, marital status, education, income, presence of diabetes, blood pressure, BMI, and other socioeconomic factors) and visual impairment. Variables identified as significant (P < 0.05) were retained as risk factors in multivariate models. Statistical analyses were performed using commercial analytical software (STATA, Version 8.2; Stata Corp., College Station, TX). 
Results
Table 1 shows the baseline characteristics of the 3280 participants. Among the responders, 553 (16.9%) had inadequate reading literacy and 688 (21.0%) had inadequate writing literacy. People with inadequate literacy were more likely to be older, to be female, to be overweight, to have diabetes mellitus, to be a smoker, to have a low educational level, to have a low income level, and to live in a worse house, than those with adequate literacy (all P < 0.001). 
Table 1.
 
Sociodemographic and Clinical Characteristics of the Participants in the Singapore Malay Eye Study
Table 1.
 
Sociodemographic and Clinical Characteristics of the Participants in the Singapore Malay Eye Study
Variable Persons with Inadequate Reading Literacy Persons with Adequate Reading Literacy P Persons with Inadequate Writing Literacy Persons with Adequate Writing Literacy P All Persons
Age groups, y
    40–49 39 (7.1) 773 (28.4) 46 (6.7) 766 (29.7) 814 (24.8)
    50–59 83 (15.0) 873 (32.1) 106 (15.4) 850 (32.9) 957 (29.2)
    60–69 161 (29.1) 618 (22.7) 214 (31.1) 565 (21.9) 780 (23.8)
    70–80 270 (22.1) 454 (16.7) <0.001 322 (46.8) 401 (15.5) <0.001 729 (22.2)
Sex (male) 98 (17.7) 1473 (54.2) <0.001 129 (18.8) 1442 (55.9) <0.001 1571 (48.0)
BMI, kg/m2 26.5 (5.4) 26.3 (5.0) <0.001 26.5 (5.5) 26.3 (5.0) 0.47 26.4 (5.1)
Diabetes (yes) 182 (33.6) 584 (22.2) <0.001 447 (66.3) 1959 (78.5) <0.001 766 (24.2)
Current smoker (yes) 50 (9.0) 612 (22.5) <0.001 63 (9.2) 599 (23.2) <0.001 662 (20.2)
Educational level
    No formal education 456 (82.6) 225 (8.3) 536 (78.0) 1442 (5.6) 681 (20.9)
    Primary education 90 (16.3) 1685 (62.1) 145 (21.1) 1442 (55.3) 1775 (54.4)
    Secondary education 5 (0.9) 593 (21.9) 5 (0.7) 1442 (55.0) 598 (18.3)
    Polytechnic/University 1 (0.2) 210 (7.7) <0.001 1 (0.2) 1442 (55.2) <0.001 211 (6.5)
Income level
    <S$1000 130 (23.6) 285 (10.6) 158 (23.1) 1442 (55.0) 415 (12.8)
    ≥S$1000 28 (5.1) 976 (36.2) 33 (4.8) 1442 (55.9) 1004 (30.9)
    Retirement income 393 (71.3) 1434 (53.2) <0.001 493 (72.1) 1442 (55.1) <0.001 1827 (56.3)
Housing type
    1-/2-room flat 160 (29.0) 340 (12.5) 186 (27.1) 313 (12.1) 500 (15.3)
    3-/4-room flat 343 (62.1) 1909 (70.3) 433 (63.1) 1819 (70.5) 2252 (68.9)
    5-room flat/private 49 (8.9) 466 (17.2) <0.001 67 (9.8) 448 (17.4) <0.001 515 (15.8)
Figure 1 and Table 2 show the associations of inadequate literacy with presenting visual impairment (PVI) and best-corrected visual impairment (BCVI). Inadequate reading and writing literacy were significantly associated with the presence of visual impairment and poor visual functioning. In multivariate analysis, inadequate reading literacy (OR = 2.66; 95% CI: 1.91–3.72) and inadequate writing literacy (OR = 2.18; 95% CI: 1.57–3.02) remained significantly associated with the presence of PVI compared with people with adequate literacy, after controlling for age, sex, language, current smoking status, body mass index, educational level, income, marital status, occupation, and housing type. There were similar associations of inadequate reading and writing literacy with BCVI (Table 2). The significant associations with inadequate reading and writing literacy persisted in stratified analyses of different education levels and income subgroups (Table 3). There was no statistically significant interaction between inadequate reading literacy and inadequate writing literacy (P > 0.05) when we included both of them in the same multivariate model. 
Figure 1.
 
Distribution of PVI, BCVI, and visual function against age. The lines were plotted by fixing age at its mean value. A lower overall VF score indicates a poorer visual function condition.
Figure 1.
 
Distribution of PVI, BCVI, and visual function against age. The lines were plotted by fixing age at its mean value. A lower overall VF score indicates a poorer visual function condition.
Table 2.
 
Associations of Inadequate Literacy with Visual Impairment and Poor Visual Functioning
Table 2.
 
Associations of Inadequate Literacy with Visual Impairment and Poor Visual Functioning
Variable OR (95% CI) for the Presence of PVI OR (95% CI) for the Presence of BCVI Linear Regression Coefficient (95% CI) Associated with Poor Visual Function
Univariate Analysis Multivariate Analysis 1* Univariate Analysis Multivariate Analysis 1* Univariate Analysis Multivariate Analysis 2†
Inadequate reading literacy 7.45 (5.92–9.37) 2.66 (1.91–3.72) 8.67 (6.67–11.28) 2.59 (1.70–3.96) 1.04 (0.93–1.13) 0.58 (1.57–3.02)
Inadequate writing literacy 6.67 (5.42–8.21) 2.18 (1.57–3.02) 8.15 (6.29–10.58) 2.07 (1.34–3.21) 0.95 (0.86–1.04) 0.54 (0.42–0.67)
Table 3.
 
Associations of Inadequate Literacy with Visual Impairment and Poor Visual Functioning
Table 3.
 
Associations of Inadequate Literacy with Visual Impairment and Poor Visual Functioning
Variable n Odds Ratio for the Presence of PVI* Odds Ratio for the Presence of BCVI Linear Regression Coefficient (95% CI) Associated with Poor Visual Function†
Reading literacy
    Persons with no formal education 676 2.66 (1.65–4.29) 2.73 (1.59–4.68) 0.60 (0.44–0.72)
    Persons with primary education 1772 2.87 (1.64–5.01) 3.23 (1.51–6.94) 0.50 (0.31–0.70)
    Persons with income level <S$1000 412 2.26 (1.02–5.03) 1.33 (0.58–3.06) 0.88 (0.65–1.11)
    Persons with retirement income 1821 2.74 (1.83–4.12) 2.93 (1.76–4.89) 0.62 (0.26–0.88)
    Persons with income level ≥S$1000 1004 4.85 (1.70–13.81) 24.41 (1.00–59.06) 0.59 (0.41–0.69)
Writing literacy
    Persons with no formal education 676 2.45 (1.42–4.23) 3.38 (1.70–6.69) 0.54 (0.43–0.69)
    Persons with primary education 1772 2.10 (1.35–3.26) 1.47 (0.74–2.94) 0.44 (0.24–0.71)
    Persons with income level <S$1000 412 3.62 (1.58–8.33) 1.62 (0.64–4.07) 0.71 (0.53–0.87)
    Persons with retirement income 1821 1.89 (1.28–2.79) 1.94 (1.17–3.25) 0.62 (0.26–1.00)
    Persons with income level ≥S$1000 1004 1.83 (0.87–3.87) 20.88 (0.94–46.58) 0.54 (0.41–0.74)
Table 2 also shows the associations of inadequate reading and writing literacy with visual functioning score. In multivariate analysis, adjusting for presenting visual acuity and other risk factors, inadequate reading literacy (β coefficient = 0.58, 95% CI = 1.57–3.02), and inadequate writing literacy (β coefficient = 0.54, 95% CI = 0.42–0.67), remained significantly associated with visual functioning score. There was no significant interaction between presenting visual acuity and inadequate literacy (P for interaction >0.05; data not shown). 
There was also no statistically significant literacy-related bias in the overall visual function score. On the nonuniform DIF level, only one (“cooking”) showed statistically significant literacy-related bias (P = 0.002). However, there was excellent agreement between the overall visual function score and its modified overall score (excluding the literacy-related biased item “cooking”). The intraclass correlation was 0.96, suggesting that there was no systematic literacy-related bias in reporting overall visual functioning score. 
Discussion
In a population-based setting, this study documents an independent association of inadequate literacy with visual impairment and poor visual-specific functioning, after controlling for confounding socioeconomic variables such as education and income. According to the 2005 to 2008 data from the United Nations Educational, Scientific, and Cultural Organization, there are >796 million illiterate people in the world. 21 Low literacy has been considered as a “silent epidemic” 22 ; despite its high prevalence, many eye health professionals are often unaware of this association, and patients with limited literacy may not easily volunteer this information. 23 Thus, it is not surprising that very few studies have examined the contribution of limited literacy to visual impairment and visual functioning; further work is necessary in this area to confirm our data. 
Our finding that adult persons with inadequate literacy were >twofold likely to have visual impairment compared with those with adequate literacy is not surprising and is consistent with the few studies in India, 24 26 Nepal, 27 and Bangladesh 28 that people with illiteracy have a >threefold higher likelihood of having blindness compared with those who are literate. However, these previous studies have been limited by the lack of adjustment for educational level and other important socioeconomic measures (e.g., income level and housing type) in their analysis; therefore, they were unable to assess the independent contribution of literacy level on visual impairment. Our study is also consistent with several previous studies that assessed the effect of health literacy on eye disease. 4,29 33 Health literacy is the ability to read, understand, and use health care materials/information to make decisions and follow instructions for treatment. 29 In this regard, health literacy level may be more useful to reflect a patient's health-care seeking ability in a health-care setting than literacy level. One study previously showed that low health literacy, estimated by a short-form test of Functional Health Literacy in Adults (s-TOFHLA), is significantly associated with the presence of diabetic retinopathy among people with type 2 diabetes. 4 Low health literacy has also been demonstrated to be associated with poor medication adherence and worsening of visual field among patients with glaucoma. 29 33 More important, perhaps, we showed that inadequate literacy explained a substantial proportion of education-related disparity in visual impairment. In our multivariate analysis without including reading literacy, people with informal educational level had a 6.00 (95% CI = 2.71 to 13.25) odds of having presenting visual impairment, compared with those with polytechnic or university educational level. The odds were reduced to 3.39 (95% CI = 1.49 to 7.68) after the inclusion of inadequate reading literacy. This finding reflects previous reports that health literacy significantly reduces the predictive power of education-related disparities in a wide range of health status, health-related behaviors, and use of health-care service. 34 It is important to note that literacy is not synonymous with educational status, although they are highly correlated. Literacy is a unique range of abilities needed for successful functioning in everyday life and health-care seeking behaviors, whereas education level is only a measure of the qualifications achieved with school systems and does not necessarily measure real-life “education” attainment. In our study, literacy level varied widely at a given level of education, and education also varied widely at a given level of literacy (Table 1). Although the two variables were highly correlated, they did not fully overlap with each other. 
Another important finding is that 8.4% (5/598) of the persons who had a secondary educational diploma had inadequate literacy, and 0.5% (1/211) of the persons who had a polytechnic/university diploma had inadequate literacy. First, this finding is not surprising, and indeed suggests that low literacy is not limited to the “poorly educated, ” as defined just by educational attainment. In fact, similar findings have arisen from the 1992 US National Adult Literacy Survey (NALS); in the NALS, 20% of adult Americans who had a high school diploma had the lowest level of literacy, and 2% who had a college diploma had the lowest level of literacy. 35 Second, educational attainment does not necessarily reflect a person's real-life skill. In Singapore, as in other countries, there is a persistent criticism that not all schools have the same standards and that there are students who “graduate” from schools who have not effectively attained reading and writing skills. Many of our participants, particularly those who were older, were first-generation migrants from other countries (e.g., Indonesia, Malaysia). Thus, it is reasonable to assume that there is a high degree of variability in school exit and entrance examinations (including high school and college) and the examination standards are not as strict as those in contemporary Singapore. Finally, we could not exclude the possibility that a small group may have overreported their education level. 
We report that inadequate literacy was also significantly associated with poor overall vision-specific functioning, after controlling for presenting visual acuity and a range of potential risk factors. These data have important implications for improving patient-centered care service in health-care systems. Education programs designed to improve health literacy among the visually impaired may be effective in improving visual functioning and greater participation in daily activities. Conversely, in a clinical survey of 195 patients with open-angle glaucoma, Muir and colleagues 31 found that patients with low health literacy do not have a worse overall vision-related quality of life score, as measured by the National Eye Institute 25-item Visual Function Questionnaire (VFQ-25). It should be noted that our study assessed literacy level and the study reported by Muir assessed health literacy level, although this methodological difference is unlikely to explain the negative finding in the Muir study. Instead, Muir's study is limited by its small sample size and, therefore, the lack of statistical power to identify a significant difference. 31  
The strengths of this study include its population-based nature, the use of both visual impairment and visual functioning, the ability to adjust for a wide range of potential risk factors, and the use of Rasch analysis. This study is subject to several limitations as well. The major limitation lies with the use of two single-item questions as our literacy screening instrument, which is susceptible to misclassification bias and does not reflect people's true functional literacy skills. As stated previously, a screening method assessing health literacy may be more useful to reflect patient's health-care seeking ability in a health-care setting. As such, further studies are needed to validate health literacy measurement tools (e.g., s-TOFHLA, Rapid Estimate of Adult Literacy in Medicine) in ethnic Malays and to reinforce our findings. However, it is important to highlight that our screening method is convenient, cognitively not demanding, and readily acceptable. A recent systematic review also shows that the use of a single-item question of self-report reading ability is effective and acceptable for quickly identifying patients with inadequate literacy. 36 This study is also limited by its cross-sectional design, which did not allow us to ascertain whether inadequate literacy was causally associated with visual impairment and poor visual functioning. Finally, this study does not elucidate the causal pathways whereby inadequate literacy affects health. It remains unclear whether inadequate literacy is an indicator of social functioning skill or a better surrogate of unmeasured socioeconomic status than education. However, it is reasonable to expect that people with inadequate literacy have more difficulty understanding health promotion messages, managing systemic conditions (e.g., diabetes and hypertension), adopting healthy lifestyles (e.g., diet and physical activity), and having their eye disease diagnosed. These barriers may increase the risk of vision loss. After diagnosis, patients with inadequate literacy may be subject to a multitude of stressors (e.g., shame, intimidation, fear, and vulnerability); they were more likely to have poor patient-provider communication, poor working knowledge of the disease and its treatment, and poor adherence to a therapeutic regimen. Taken together, the relationship between inadequate literacy and visual impairment may occur as the result of an array of pathways that lead to a combined effect. 
In summary, we showed that inadequate literacy is an independent, potentially modifiable risk factor for visual impairment and poor visual functioning. Our findings underscore a need to develop, evaluate, and validate health literacy screening method in the Asian culture context. More broadly, our study suggests that new education programs and shared decision-making tools are needed to improve patients' generic literacy, health literacy, and medical decision quality. 37 Improving clinicians' skills and approach (e.g., “ask–tell–ask” method) in communicating with inadequate literacy patients may also result in better compliance and adherence. 38,39 Finally, identifying issues and developing strategies to improve literacy among those with visual impairment and improving patient–clinician communication will help reduce the socioeconomic disparities associated with impaired vision around the world. 
Footnotes
 Supported in part by Biomedical Research Council Grant 08/1/35/19/550 and National Medical Research Council Grant StaR/0003/2008, Singapore.
Footnotes
 Disclosure: Y. Zheng, None; E. Lamoureux, None; P.P.-C. Chiang, None; C.-Y. Cheng, None; A.R. Anuar, None; S.-M. Saw, None; T. Aung, None; T.Y. Wong, None
References
Gazmararian JA Baker DW Williams MV . Health literacy among Medicare enrollees in a managed care organization. J Am Med Assoc. 1999;281:545–551. [CrossRef]
Williams MV Parker RM Baker DW . Inadequate functional health literacy among patients at two public hospitals. J Am Med Assoc. 1995;274:1677–1682. [CrossRef]
Wolf MS Gazmararian JA Baker DW . Health literacy and functional health status among older adults. Arch Intern Med. 2005;165:1946–1952. [CrossRef] [PubMed]
Schillinger D Grumbach K Piette J . Association of health literacy with diabetes outcomes. J Am Med Assoc. 2002;288:475–482. [CrossRef]
Evangelista LS Rasmusson KD Laramee AS . Health literacy and the patient with heart failure—implications for patient care and research: a consensus statement of the Heart Failure Society of America. J Card Fail. 2010;16:9–16. [CrossRef] [PubMed]
Baker DW Gazmararian JA Williams MV . Health literacy and use of outpatient physician services by Medicare managed care enrollees. J Gen Intern Med. 2004;19:215–220. [CrossRef] [PubMed]
Baker DW Wolf MS Feinglass J Thompson JA Gazmararian JA Huang J . Health literacy and mortality among elderly persons. Arch Intern Med. 2007;167:1503–1509. [CrossRef] [PubMed]
Dewalt DA Berkman ND Sheridan S Lohr KN Pignone MP . Literacy and health outcomes: a systematic review of the literature. J Gen Intern Med. 2004;19:1228–1239. [CrossRef] [PubMed]
Pignone M DeWalt DA Sheridan S Berkman N Lohr KN . Interventions to improve health outcomes for patients with low literacy. A systematic review. J Gen Intern Med. 2005;20:185–192. [CrossRef] [PubMed]
Hahn EA Du H Garcia SF . Literacy-fair measurement of health-related quality of life will facilitate comparative effectiveness research in Spanish-speaking cancer outpatients. Med Care. 2010;48:S75–S82. [CrossRef] [PubMed]
Hahn EA Cella D Dobrez DG . The impact of literacy on health-related quality of life measurement and outcomes in cancer outpatients. Qual Life Res. 2007;16:495–507. [CrossRef] [PubMed]
Tielsch JM Steinberg EP Cassard SD . Preoperative functional expectations and postoperative outcomes among patients undergoing first eye cataract surgery. Arch Ophthalmol. 1995;113:1312–1318. [CrossRef] [PubMed]
Swamy BN Chia EM Wang JJ Rochtchina E Mitchell P . Correlation between vision- and health-related quality of life scores. Acta Ophthalmol. 2009;87:335–339. [CrossRef] [PubMed]
Foong AW Saw SM Loo JL . Rationale and methodology for a population-based study of eye diseases in Malay people: the Singapore Malay Eye Study (SiMES). Ophthalmic Epidemiol. 2007;14:25–35. [CrossRef] [PubMed]
Wong TY Chong EW Wong WL . Prevalence and causes of low vision and blindness in an urban Malay population: the Singapore Malay Eye Study. Arch Ophthalmol. 2008;126:1091–1099. [CrossRef] [PubMed]
Lamoureux EL Pesudovs K Thumboo J Saw SM Wong TY . An evaluation of the reliability and validity of the visual functioning questionnaire (VF-11) using Rasch analysis in an Asian population. Invest Ophthalmol Vis Sci. 2009;50:2607–2613. [CrossRef] [PubMed]
Lamoureux EL Chong E Wang JJ . Visual impairment, causes of vision loss, and falls: the Singapore Malay Eye Study. Invest Ophthalmol Vis Sci. 2008;49:528–533. [CrossRef] [PubMed]
Lamoureux EL Chong EW Thumboo J . Vision impairment, ocular conditions, and vision-specific function: the Singapore Malay Eye Study. Ophthalmology. 2008;115:1973–1981. [CrossRef] [PubMed]
Lamoureux EL Saw SM Thumboo J . The impact of corrected and uncorrected refractive error on visual functioning: the Singapore Malay Eye Study. Invest Ophthalmol Vis Sci. 2009;50:2614–2620. [CrossRef] [PubMed]
Lamoureux EL Tai ES Thumboo J . Impact of diabetic retinopathy on vision-specific function. Ophthalmology. 2010;117:757–765. [CrossRef] [PubMed]
Regional literacy rates for youths (15–24) and adults (15+). Available at: http://stats.uis.unesco.org/unesco/TableViewer/tableView.aspx?ReportId=201 Accessed on March 31, 2011.
Marcus EN . The silent epidemic—the health effects of illiteracy. N Engl J Med. 2006;355:339–341. [CrossRef] [PubMed]
Farrell TW Chandran R Gramling R . Understanding the role of shame in the clinical assessment of health literacy. Fam Med. 2008;40:235–236. [PubMed]
Nirmalan PK Thulasiraj RD Maneksha V . A population based eye survey of older adults in Tirunelveli district of south India: blindness, cataract surgery, and visual outcomes. Br J Ophthalmol. 2002;86:505–512. [CrossRef] [PubMed]
Vijaya L George R Arvind H . Prevalence and causes of blindness in the rural population of the Chennai Glaucoma Study. Br J Ophthalmol. 2006;90:407–410. [CrossRef] [PubMed]
Murthy GV Gupta SK Bachani D Jose R John N . Current estimates of blindness in India. Br J Ophthalmol. 2005;89:257–260. [CrossRef] [PubMed]
Sapkota YD Pokharel GP Nirmalan PK Dulal S Maharjan IM Prakash K . Prevalence of blindness and cataract surgery in Gandaki Zone. Nepal Br J Ophthalmol. 2006;90:411–416. [CrossRef]
Dineen BP Bourne RR Ali SM Huq DM Johnson GJ . Prevalence and causes of blindness and visual impairment in Bangladeshi adults: results of the National Blindness and Low Vision Survey of Bangladesh. Br J Ophthalmol. 2003;87:820–828. [CrossRef] [PubMed]
Muir KW Lee PP . Health literacy and ophthalmic patient education. Surv Ophthalmol. 2010;55:454–459. [CrossRef] [PubMed]
Muir KW Lee PP . Literacy and informed consent: a case for literacy screening in glaucoma research. Arch Ophthalmol. 2009;127:698–699. [CrossRef] [PubMed]
Muir KW Santiago-Turla C Stinnett SS . Health literacy and vision-related quality of life. Br J Ophthalmol. 2008;92:779–782. [CrossRef] [PubMed]
Muir KW Santiago-Turla C Stinnett SS . Health literacy and adherence to glaucoma therapy. Am J Ophthalmol. 2006;142:223–226. [CrossRef] [PubMed]
Lee PP . Why literacy matters. Links between reading ability and health. Arch Ophthalmol. 1999;117:100–1003. [CrossRef] [PubMed]
Bennett IM Chen J Soroui JS White S . The contribution of health literacy to disparities in self-rated health status and preventive health behaviors in older adults. Ann Fam Med. 2009;7:204–211. [CrossRef] [PubMed]
Kaestle CF Campbell A Finn JD Johnson ST Mikulecky LJ . Adult Literacy and Education in America: Four Studies Based on the National Adult Literacy Survey. Washington, DC: National Center for Education Statistics; 2001.
Powers BJ Trinh JV Bosworth HB . Can this patient read and understand written health information? J Am Med Assoc. 2010;304:76–84. [CrossRef]
Randall T . Producers of videodisc programs strive to expand patient's role in medical decision-making process. J Am Med Assoc. 1993;270:160–162. [CrossRef]
Friedman DS Hahn SR Quigley HA . Doctor–patient communication in glaucoma care: analysis of videotaped encounters in community-based office practice. Ophthalmology. 2009;116:2277–2285. [CrossRef] [PubMed]
Hahn SR Friedman DS Quigley HA . Effect of patient-centered communication training on discussion and detection of non adherence in glaucoma. Ophthalmology. 2010;117:1339–1347. [CrossRef] [PubMed]
Figure 1.
 
Distribution of PVI, BCVI, and visual function against age. The lines were plotted by fixing age at its mean value. A lower overall VF score indicates a poorer visual function condition.
Figure 1.
 
Distribution of PVI, BCVI, and visual function against age. The lines were plotted by fixing age at its mean value. A lower overall VF score indicates a poorer visual function condition.
Table 1.
 
Sociodemographic and Clinical Characteristics of the Participants in the Singapore Malay Eye Study
Table 1.
 
Sociodemographic and Clinical Characteristics of the Participants in the Singapore Malay Eye Study
Variable Persons with Inadequate Reading Literacy Persons with Adequate Reading Literacy P Persons with Inadequate Writing Literacy Persons with Adequate Writing Literacy P All Persons
Age groups, y
    40–49 39 (7.1) 773 (28.4) 46 (6.7) 766 (29.7) 814 (24.8)
    50–59 83 (15.0) 873 (32.1) 106 (15.4) 850 (32.9) 957 (29.2)
    60–69 161 (29.1) 618 (22.7) 214 (31.1) 565 (21.9) 780 (23.8)
    70–80 270 (22.1) 454 (16.7) <0.001 322 (46.8) 401 (15.5) <0.001 729 (22.2)
Sex (male) 98 (17.7) 1473 (54.2) <0.001 129 (18.8) 1442 (55.9) <0.001 1571 (48.0)
BMI, kg/m2 26.5 (5.4) 26.3 (5.0) <0.001 26.5 (5.5) 26.3 (5.0) 0.47 26.4 (5.1)
Diabetes (yes) 182 (33.6) 584 (22.2) <0.001 447 (66.3) 1959 (78.5) <0.001 766 (24.2)
Current smoker (yes) 50 (9.0) 612 (22.5) <0.001 63 (9.2) 599 (23.2) <0.001 662 (20.2)
Educational level
    No formal education 456 (82.6) 225 (8.3) 536 (78.0) 1442 (5.6) 681 (20.9)
    Primary education 90 (16.3) 1685 (62.1) 145 (21.1) 1442 (55.3) 1775 (54.4)
    Secondary education 5 (0.9) 593 (21.9) 5 (0.7) 1442 (55.0) 598 (18.3)
    Polytechnic/University 1 (0.2) 210 (7.7) <0.001 1 (0.2) 1442 (55.2) <0.001 211 (6.5)
Income level
    <S$1000 130 (23.6) 285 (10.6) 158 (23.1) 1442 (55.0) 415 (12.8)
    ≥S$1000 28 (5.1) 976 (36.2) 33 (4.8) 1442 (55.9) 1004 (30.9)
    Retirement income 393 (71.3) 1434 (53.2) <0.001 493 (72.1) 1442 (55.1) <0.001 1827 (56.3)
Housing type
    1-/2-room flat 160 (29.0) 340 (12.5) 186 (27.1) 313 (12.1) 500 (15.3)
    3-/4-room flat 343 (62.1) 1909 (70.3) 433 (63.1) 1819 (70.5) 2252 (68.9)
    5-room flat/private 49 (8.9) 466 (17.2) <0.001 67 (9.8) 448 (17.4) <0.001 515 (15.8)
Table 2.
 
Associations of Inadequate Literacy with Visual Impairment and Poor Visual Functioning
Table 2.
 
Associations of Inadequate Literacy with Visual Impairment and Poor Visual Functioning
Variable OR (95% CI) for the Presence of PVI OR (95% CI) for the Presence of BCVI Linear Regression Coefficient (95% CI) Associated with Poor Visual Function
Univariate Analysis Multivariate Analysis 1* Univariate Analysis Multivariate Analysis 1* Univariate Analysis Multivariate Analysis 2†
Inadequate reading literacy 7.45 (5.92–9.37) 2.66 (1.91–3.72) 8.67 (6.67–11.28) 2.59 (1.70–3.96) 1.04 (0.93–1.13) 0.58 (1.57–3.02)
Inadequate writing literacy 6.67 (5.42–8.21) 2.18 (1.57–3.02) 8.15 (6.29–10.58) 2.07 (1.34–3.21) 0.95 (0.86–1.04) 0.54 (0.42–0.67)
Table 3.
 
Associations of Inadequate Literacy with Visual Impairment and Poor Visual Functioning
Table 3.
 
Associations of Inadequate Literacy with Visual Impairment and Poor Visual Functioning
Variable n Odds Ratio for the Presence of PVI* Odds Ratio for the Presence of BCVI Linear Regression Coefficient (95% CI) Associated with Poor Visual Function†
Reading literacy
    Persons with no formal education 676 2.66 (1.65–4.29) 2.73 (1.59–4.68) 0.60 (0.44–0.72)
    Persons with primary education 1772 2.87 (1.64–5.01) 3.23 (1.51–6.94) 0.50 (0.31–0.70)
    Persons with income level <S$1000 412 2.26 (1.02–5.03) 1.33 (0.58–3.06) 0.88 (0.65–1.11)
    Persons with retirement income 1821 2.74 (1.83–4.12) 2.93 (1.76–4.89) 0.62 (0.26–0.88)
    Persons with income level ≥S$1000 1004 4.85 (1.70–13.81) 24.41 (1.00–59.06) 0.59 (0.41–0.69)
Writing literacy
    Persons with no formal education 676 2.45 (1.42–4.23) 3.38 (1.70–6.69) 0.54 (0.43–0.69)
    Persons with primary education 1772 2.10 (1.35–3.26) 1.47 (0.74–2.94) 0.44 (0.24–0.71)
    Persons with income level <S$1000 412 3.62 (1.58–8.33) 1.62 (0.64–4.07) 0.71 (0.53–0.87)
    Persons with retirement income 1821 1.89 (1.28–2.79) 1.94 (1.17–3.25) 0.62 (0.26–1.00)
    Persons with income level ≥S$1000 1004 1.83 (0.87–3.87) 20.88 (0.94–46.58) 0.54 (0.41–0.74)
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×