Frequency, Course, and Impact of Correctable Visual Impairment (Uncorrected Refractive Error)

SURVEY OF OPHTHALMOLOGY

VOLUME 55  NUMBER 6  NOVEMBER–DECEMBER 2010

MAJOR REVIEW

Frequency, Course, and Impact of Correctable Visual Impairment (Uncorrected Refractive Error) Julie Schneider, BAppSc (Hons), PhD,1 Stephen R. Leeder, MD, PhD,1 Bamini Gopinath, BTech (Hons), PhD,2 Jie Jin Wang, MMed, PhD,2,3 and Paul Mitchell, MD, PhD2 1

Menzies Centre for Health Policy, University of Sydney, Sydney, Australia; 2Centre for Vision Research, Department of Ophthalmology and Westmead Millennium Institute, University of Sydney, Sydney, Australia; and 3Centre for Eye Research Australia, University of Melbourne, Melbourne, Australia

Abstract. Uncorrected refractive error has been identified by the World Health Organization (WHO) as one of the priorities for Vision 2020 and a frequent cause of visual impairment. In the past, only the terms presenting visual impairment (PVI) and visual impairment after best refractive correction (BCVI) were used, so that PVI also included BCVI cases. In the more recent literature, visual impairment has been subdivided into two mutually exclusive entities: that which is correctable by refraction (which we now term correctable visual impairment, CVI) and that which cannot be corrected by refraction due to ocular or neurological disease (which we now term non-correctable visual impairment, NCVI, and which is identical to BCVI). PVI remains a useful concept as it includes both types of impairment. Although CVI is reported to be the major form of visual impairment worldwide, its impacts are not yet well understood. CVI has a higher prevalence among vulnerable groups such as older people, less well educated people and those living alone or in rural areas. Systematic data on barriers to refractive correction remain scant, but these may be present at the individual level, within the health service context, or at a social level. Our review indicates that research on CVI is at a relatively early stage and that more detailed research, particularly determining whether it has impacts on independent living and quality of life, is needed before CVI can be justifiably prioritized in health policy. (Surv Ophthalmol 55:539--560, 2010. Ó 2010 Elsevier Inc. All rights reserved.) Key words. refractive error  correctable visual impairment impairment  uncorrected refractive error  adults  children

I. Introduction



presenting

visual

the Vision 2020 priority areas, together with disease states leading to visual impairment that cannot be corrected by refraction--such as cataract, trachoma, onchocerciasis, childhood blindness, low vision, glaucoma, diabetic retinopathy and age-related macular degeneration (AMD). Historically, blindness was defined using a measure of best corrected visual acuity. Past prevalence studies of visual impairment mostly adhered to this definition. This has meant that individuals who experience

A. THE EMERGENCE OF ‘CORRECTABLE’ VISUAL IMPAIRMENT AS A GLOBAL HEALTH CHALLENGE

The World Health Organization (WHO) and the International Agency for the Prevention of Blindness (IAPB) have now recognized the significance of uncorrected refractive error in their Vision 2020 global quest for the prevention of avoidable blindness. Refractive error is identified as one of 539 Ó 2010 by Elsevier Inc. All rights reserved.

0039-6257/$ - see front matter doi:10.1016/j.survophthal.2010.02.004

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difficulty in daily visual function as the result of uncorrected or under-corrected refractive error were overlooked. Several authors drew attention to this96,104 and sparked a wider recognition of the condition of uncorrected refractive error or correctable visual impairment (CVI). Subsequently, several researchers identified the prevalence of CVI by assessing both presenting visual impairment (PVI; habitual, i.e., with glasses if worn) and visual impairment after best-correction (BCVI). CVI can be defined as PVI correctable by refraction, and the remaining BCVI cases can alternately be termed as non-correctable visual impairment (NCVI). There is a subtle difference between the terminology of uncorrected refractive error, which suggests that visual impairment may or may not exist if refractive error is not corrected, and CVI, which implies that visual impairment is present when there is no or inadequate refractive correction. In this review, the term CVI is used in preference to uncorrected refractive error, as it more precisely defines a state of visual impairment, although the title of our review includes both terms. Vision 2020 has argued for the definition of visual impairment and blindness to be altered to include uncorrected refractive error (CVI) in the International Classification of Diseases.18 The WHO recently estimated that CVI accounts for 153 million cases of visual impairment globally, making it the major cause of mild to moderate levels of visual impairment worldwide.86 Several large scale regional surveys have recently reached similar conclusions.21,66,67,94,98,102 The focus of the WHO review by Resnikoff et al86 provided estimates of the prevalence of CVI. Although it highlighted the magnitude of this problem as a public health concern, the authors did not, however, elaborate on the specific factors associated with CVI or the impacts of CVI, particularly in children, and did not highlight the relative paucity of data. The current review aims to extend the summary by Resnikoff et al,86 as well as detail studies focusing on these latter important areas of CVI research. We review the international literature in order to address the following questions:    

How frequent is CVI? Over time, what is the course of CVI? What factors are associated with CVI? What are the impacts of CVI?

A secondary question explored in the discussion is:  What are the reasons for CVI? That is, what barriers exist with regard to visual assessment and spectacle ownership and use? Within all sections, data on both children and adults are considered where available. The review concludes with a discussion of the reasons for CVI

SCHNEIDER ET AL

and outlines important areas and priorities for further research.

II. Methods A. LITERATURE SEARCH STRATEGY

Literature searches were conducted for the years 1996--2008 via Ovid (e.g., Medline, CINAHL); Informit (Health, Social Science), and Web of Science. Key words used included: correctable visual impairment, under-correction, uncorrected, refractive error, unmet, uncorrected, avoidable, preventable, spectacles, glasses, children, adults, elderly, barriers, eye health services, population. Our review is limited to peer-reviewed papers published in English, but includes all age groups. English abstract search results were collected and screened to remove any articles clearly not relevant to the topic, those reporting only best-corrected visual performance, and those reporting only refractive error prevalence without assessing the extent of unmet need for correction. Additional earlier or key studies were identified from article reference lists. We included largely population-based epidemiological studies, as well as smaller empirical investigations, reviews, and editorials/commentaries. B. IMPORTANT METHODOLOGICAL ISSUES IDENTIFIED

Several methodological concerns arose that made comparison between studies problematic. First, it was evident that studies have often used different definitions for visual impairment and blindness. Typically, either the WHO definition or a countryspecific definition of blindness was applied. For example, the definition of legal blindness in the United States,104 Australia,98 and many other countries is a VA of 20/200 or worse, whereas WHO defines blindness as a VA less than 20/400.15,104 Visual impairment definitions (‘‘low vision’’) also vary from a VA worse than 20/40,98,104 the binocular legal requirement for driving in many countries, to the WHO definition15 of a VA worse than 20/60. Second, studies apply varying definitions or terminology to refer to visual impairment caused by refractive error. Some have used the term ‘‘correctable’’ visual impairment whereas others report on levels of ‘‘under-correction’’. The former suggests that impairment can be removed totally by refraction, and the latter suggests that impairment can be reduced by correction. Most frequently, correctable or under-corrected visual impairment is defined as impairment that corrects to better than a specified level of acuity (such as 20/60 or 20/40) or as a particular degree of improvement, such as improvement by 1 line or by 3 lines on a Snellen chart. We

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UNCORRECTED REFRACTIVE ERROR

include articles reporting on both uncorrected and under-corrected visual impairment and both are referred to by the term CVI. Third, how VA improvement is assessed differs. Some researchers have used the pinhole method, whereas others have used automated refraction, subjective refraction, or a combination. The pinhole method may be less accurate and could lead to an underestimation of ocular disease.5,50 Particularly in studies of children, multiple methods are deemed most appropriate. We include articles using all of these, but take care to note these methodological variations in the summary tables provided. Further, not all studies provided a clear description of the causal factors for the visual impairment. Other relevant issues included: (a) the use of the term ‘‘better eye’’ in some studies and ‘‘worse eye’’ in others; and (b) presentation of unilateral VI versus bilateral VI. In addition, authors have employed different methods of reporting or communicating their data. Some have reported CVI in terms of prevalence within the total population, some as a proportion of those with PVI, and others as a proportion of those with refractive error. To clarify the magnitude of CVI in this review, it is expressed in terms of prevalence within the study population and/or as a proportion of the visual impairment and blindness reported. Finally, various study designs have been used. Population-based research offers a more accurate measure of prevalence than estimates from samples of selected subpopulations. For example, if a study samples participants in general practices or eye clinics, selection bias is introduced as only people accessing health services are reached. Studies of children, particularly those reporting impacts of CVI, have often relied on school-derived rather than representative samples, and not always included cycloplegic refraction in the research protocol. Similarly, designs excluding institutional residents and assessing only community-dwelling residents are limited by possible underestimation of prevalence. Many studies have shown that the prevalence of visual impairment is higher among those in long-term residential care.64,103 In this review, smaller studies of selected subpopulations were not included when discussing prevalence findings (section IIIA) and the scope of population samples (community only or community plus institutional) is noted.

III. Findings A. FREQUENCY OF CORRECTABLE VISUAL IMPAIRMENT

Over 50 articles were located that reported specifically on, or made reference to, the prevalence

of CVI among adults (n 5 30), children (n 5 15), or both (n 5 9) throughout the UK, USA, South America, South and South East Asia, Africa, Middle East, and Australia. Prevalence studies indicate that CVI is a major cause of low vision in both developing and developed countries. CVI is also reported to a lesser degree, and more so in developing countries, as a cause of blindness. 1. Studies That Included Only Children Beginning in 1998, the Refractive Error Study in Children (RESC) was conducted in China, Nepal, Chile, India, South Africa, and Malaysia, using a population-based method and logarithm of the minimum angle of resolution (LogMAR) protocol to assess children aged 5--15 years. The RESC testing and examination protocol included standardized VA measurements (presenting, uncorrected and bestcorrected using a retro-illuminated LogMAR chart with five tumbling E optotypes or letters on each line), lensometry when appropriate, ocular motility and eye alignment evaluation, cycloplegia (using two drops of cyclopentolate 1% administered 5 minutes apart), retinoscopy, autorefraction, and examination of the anterior segments, media, and fundi.69 In the RESC studies, the prevalence of PVI (#20/ 40) ranged from 1.2%69 to 14.7%.62 The proportion of children whose vision could be improved with glasses to 20/32 or better ranged from as low as 0.9% in South Africa69 to 9% and higher in China.44,120 The higher prevalence of CVI in East Asian children represents a potentially important public health concern in this region. Table 1 records the prevalence of visual impairment in terms of PVI and BCVI. Across all studies, the majority of reduced vision (between 56% and 94%) was found to be caused by refractive error. Other studies of visual impairment in children have identified different levels of CVI. In a large study of Australian 6-year-old school children (n 5 1,723)89 a relatively small number of participants (1.5%) had CVI and could have benefited from glasses. Among 12-year-old children (n 5 2,353) the prevalence of PVI (!20/40) in the worse eye was 5%, and in the majority (82%) this was correctable (improving 2þ lines) by refraction.87 Most children with refractive error in this study were already adequately corrected with appropriate glasses. Only 1.9% were considered either in need of spectacles (n 5 8) or a change to their existing prescription (n 5 37).88 In contrast to the Australian findings, much higher CVI levels have been reported elsewhere using the RESC protocol and definition of visual impairment (#20/40) for both eyes. Among 2,454 teens (aged 13--17 years) in rural southern China,

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TABLE 1

Refractive Error Studies in Children—Prevalence of Visual Impairment (VI) and Uncorrected Refractive Error in Children Based on Measured Visual Acuity (VA)

Region China120 Nepal79 Chile62 New Delhi68 South Africa69 Iran48 Malaysia38; b India22; b China43,44

Prevalence of VIa (using presenting VA) (%)

Prevalence of VI (using best-corrected VA) (%)

Proportion Uncorrected (%)

10.9 2.8 7.3 4.9 1.2 3.6 10.1 2.6 10.3

0.8 1.4 3.3 0.81 0.32 0.7 1.4 0.78 0.62

9.1 1.4 4.0 4.1 0.88 2.9 8.7 1.8 9.7

VA 5 visual acuity; VI 5 visual impairment. Visual impairment was defined as a visual acuity of 20/40 or worse b The Malaysian and Indian studies deviated slightly from the others in that only children aged 7--15 years old were assessed. a

He et al42 reported a prevalence of PVI in the better eye of 16.6%. More than 98% of these children were able to achieve normal/near normal vision (20/32 or better) in at least one eye with refraction, resulting in a CVI prevalence of over 16%. Less than half of those with CVI wore glasses. A recent study in Egypt among 7- to 14-year-old children (n 5 5,839) similarly found that less than half those with refractive error (22% refractive error prevalence) wore glasses.28 A prevalence of PVI (# 20/40) in the better eye of 9.1% was reported among 4,282 teens (aged 10--15 years) in Kathmandu Nepal using the RESC protocol.93 Over 90% of this impairment was due to CVI (8.2% CVI prevalence). 2. Studies That Included Both Children and Adults A large number of participants aged 12 years and over (n 5 13,265) had vision data collected as part of the US National Health and Nutrition Examination Survey (1999--2002). Data collection included VA and automated refraction with habitual correction, if any. The prevalence of PVI (#20/50) was 6.4%, with most due to uncorrected refractive error (5.3% of participants had CVI and 1.1% had NCVI). However, the CVI prevalence decreased to 4.1% when those who forgot to bring their glasses to the assessment were discounted.108 Similar prevalence rates have been found elsewhere, as shown in Table 2. In India, the adjusted prevalence of moderate visual impairment (presenting VA !20/60 to 20/ 200) and blindness (!20/200) was reported as 8.1% and 1.84%, respectively.17,21 CVI was responsible for 45.8% of moderate impairment and for 16.3% of blindness.17,21 In Iran, the PVI prevalence (!20/60) was 2.52% among participants aged 5

years and older, with CVI responsible for 33.6% of these cases.35 Further analysis revealed that 4.8% of the total study population (n 5 4,565) had an unmet need for spectacles. Surprisingly, a majority of those with PVI (62%) could improve by four or more lines in VA with appropriate correction.35 In Lebanon, Mansour et al61 reported 3.9% prevalence of low vision (!20/60). Around half of those with low vision were able to improve with pinhole and would no longer be vision impaired according to the WHO definition. 3. Studies That Included Only Adults One of the earlier studies to record the prevalence of CVI was the Baltimore Eye Survey of 5,300 white and black non-institutionalized Americans.104 Applying the WHO definition, Tieslch et al identified a PVI (!20/60) prevalence of 3.71% and 4.40% among whites and blacks, respectively. The prevalence of blindness (!20/400) was 0.58% and 0.92%. Over half the visual impairment among both races (65.7% and 57.1% for whites and blacks respectively), and smaller proportions of the blindness (11.8% and 15.4%, respectively) was due to inadequately corrected refractive error. The authors reported that more than half of all participants in the study had their vision improved with refraction. In the United Kingdom, 1,362 community and institutionalized adults aged 65 years and over had VA measured as part of their participation in the National Diet and Nutrition Survey in 1994--1995. PVI prevalence of 14.3% was reported using the WHO definition (!20/60) and it was noted that one in five participants in the sample (21.2%) were able to improve their vision by one or more lines with pinhole.105

Reports of the Frequency of Correctable Visual Impairment (CVI); Most Recent First Region; year

Population

Frequency of VI

Frequency of CVI

Los Angeles; 20091

n 5 3,835; 30--72 months

5.9% in African American and 7.1% in Hispanic

4.3% in African-American and 5.3% in Hispanic

China; 200947

n 5 1,399; 50þ years.

China; 200960

n 5 17,699; 3--6 yrs

VI: 10.1%. Prevalence of blindness: 0.6% 0.43%

CVI: 7.0%. Among blindness; 0.1% due to CVI 0.32%

Nigeria; 20092

n 5 13,591; 40þ yrs

23.1%

11.7%

Poland; 200973

n 5 969; 18--34 yrs

13.2%

12.0%

China; 200814

n 5 1,892; 11.4--17.1 yrs

79.9%

76.9%

Brazil; 200892

n 5 2,411; 11--14 yrs

VI ($20/40): 4.8%

2.5%

Malaysia; 200841

n 5 712; 6--12 yrs

7.7%

7.0%

Singapore Malay; 2008115

n 5 3,269; 40--79 yrs

8.8%

6.1%

India; 200870

n 5 40,447; 50þ yrs

Global review; 200886

Review of various surveys across WHO regions; 5þ yrs n 5 1,361; 65þ yrs

VI prevalence 16.8%. Prevalence of severe VI 4.4%. Prevalence of blindness 3.6% 8 million are blind

CVI: 9.1%. Among severe VI; 8.1% due to CVI. Among blindness; 1.4% due to CVI Estimated: 153 million worldwide with VI due to CVI

17%

9.55%; 71% gained 3þ lines; 34% gained 5þ lines CVI prevalence: 17.8%. Among blindness cases; 2.8% was due to CVI

Chinese Taiwan; 200757 Myanmar; 20078

n 5 2,076; 40þ yrs

VI prevalence 40.4%. Prevalence of blindness 8.1%

Definition of ‘‘Correctable’’ Impairment Visually significant uncorrected refractive error was defined a priori as spherical equivalent (SE) myopia of $0.5 D or more; SE hyperopia of $3.0 D; astigmatism (any axis) of $2.0 D if 30 to 36 months old; or $1.5 D for children O36 months of age Improvement to 20/40 or better with automated refraction Improvement to 20/60 or better with pinhole Improving with automated refraction to 20/60 or better Improving with refraction to 20/40 or better Improving with automated refraction to 20/40 or better Not specified. Deemed able to benefit from glasses Improving with pinhole to 20/40 or better Improvement of at least 0.2 Logmar (equivalent to 2 lines) in the best-corrected VA in the better eye compared with the presenting VA Improving to 20/60 or better with pinhole

UNCORRECTED REFRACTIVE ERROR

TABLE 2

Improving to 20/60 or better with pinhole or refraction Improving to better than 20/40 on refraction Improving with pinhole to better than 20/60 (VI) or better than 10/200 (blindness) 543

(Continued on the next page)

Population

Frequency of VI

Timor-Leste; 200782,83

n 5 1,414; 40þ yrs

17.7%. Prevalence of blindness 7.4%.

Australia; 200610 Blue Mountains Eye Study (BMES); extension Australia; 200665 Visual Impairment Project (VIP); Melbourne US; 2006108 National Health and Nutrition Examination Survey (NHANES) 1999--2002 Tehran; Iran; 200635

n 5 892; 49þ yrs

Frequency of CVI

Definition of ‘‘Correctable’’ Impairment Improving with pinhole to better than 20/60

4.5%

12.9%. Among blindness cases; 5.5% due to CVI. Age, gender and domicileadjusted CVI prevalence 14.9% 3.5%

n 5 1,695; 40þ yrs

8%

5.8%

Improving with pinhole or auto refraction to 20/40 or better

n 5 13,265 with complete vision data; 12þ yrs

6.4%

5.3% (4.1% discounting those who forgot glasses)

Improving with automated refraction to 20/40 or better

n 5 4,353; 5þ yrs

7.1%

Papua New Guinea; 200637 Cameroon; Africa; 200677

n 5 1,174; 50þ yrs

29.2%

4.8% of total population had unmet need for spectacles Adjusted prevalence 13.1%

n 5 1,787; 40þ yrs

VI: 6.4%; severe VI: 2.2%; and blindness: 1.6%

Improving with refraction to 20/ 40 or better Improving with pinhole to better than 20/60 Improving with pinhole to better than 20/60

Australia; 200598 Combined VIP and BMES-I

n 5 8,909; 40þ yrs

Australia; 200411 BMES-II Bangladesh; 20046

n 5 3,154 with complete vision data; 49þ yrs n 5 11,624; 30þ yrs

VI prevalence ranged from 0.7% (among those 40--49 yrs) to 39.5% (among those over 90 yrs). Prevalence of blindness ranged from 0% (among those 40--49 yrs) to 16.9% (among those over 90 yrs) 7.5%

UK; 200430 MRC Trial Tehran; Iran; 200434

Improving with refraction to 20/ 40 or better

5.5%

n 5 14,403; 75þ yrs

Spectacle coverage of 25.2% for 20/40 cutoff and 40.5% for 20/60 12%

Improving with refraction to 20/ 40 or better Improving with automated refraction to 20/40 or 20/60

3.2%

n 5 4,565; all ages

2.9%

1.0%

n 5 1,152; 40þ yrs

5.3%

3.5%

Improving with pinhole to better than 20/60 Improving with refraction to 20/ 60 or better Improving with refraction 2þ lines

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Singaporean Chinese; 200494

CVI: 1.7%. Among severe VI; 15% due to CVI. Among blindness 0 were due to CVI 62% of VI and 4% of blindness was due to CVI

Improving with refraction to 20/ 40 or better

Surv Ophthalmol 55 (6) November--December 2010

Region; year

544

TABLE 2 (Continued)

n 5 2,530; 40þ yrs

4.2%

2.5%

Improving with refraction 1þ line

n 5 3,654; 49þ yrs

14%

9.5%

n 5 11,462; 50þ yrs

18.97% (#20/100)

42.7% of those screened had spectacles prescribed

Improving with refraction to 20/ 32 or better Not specified. Deemed able to benefit from glasses

n 5 5,150; 40þ yrs

41.1%

28.8% (improving by 1þ line)

Bangladesh; 200325

n 5 11,624; 30þ yrs

13.8%

2.6%

Australia; 2002101 BMES-I

n 5 3,654; 49þ yrs

22.3%

CVI:10.3%. Approx half improved 3þ lines

Australia; 200232,33 BMES-I & II

Reports 2 cross-sections; BMES--I; n 5 3,654; BMES--II; n 5 3509; 49þ yrs n 5 10,293; all ages

Approx 2/3 of VI due to CVI

BMES-I: 7.5% CVI and 3.6% NCVI; BMES-II: 5.6% CVI and 2.7% NCVI

Moderate VI: 8.1%

3.7%

Improving with refraction from moderate VI (20/60--20/200)

n 5 4,774; 40þ yrs

8.2%

Improving with subjective refraction to 20/40 or better

Hong Kong; 200263

n 5 3,441; 60þ yrs

19.5%

CVI: 6.0%. 77% improved 2þ lines; 14% improved 6þ lines 13.4%

Jordan; 200240

n 5 720; 45þ yrs with blindness or VI attending hospital

India; 200117 Andhra Pradesh Eye Study Australia; 2000112 VIP

n 5 10,293; all ages

CVI caused 17% of low vision; 1.6% of blindness; and was the 2nd most common cause of VI behind cataract. Prevalence of blindness 1.84%

CVI: 0.3%

Improving with refraction from 10/200 or worse

UK; 2000105 National diet and nutrition survey Australia; 199959 VIP India; 199916 Andhra Pradesh Eye Study

n 5 1,362; 65þ yrs with vision measured

India; 200221 Andhra Pradesh Study Mexican American; 200267

n 5 5,147; 40þ yrs

Improved with subjective refraction from !20/60 Improving with auto refraction to 20/40 or better VA less than 20/30 and improving with refraction by 2þ lines Improving with refraction to 20/ 40 or better

UNCORRECTED REFRACTIVE ERROR

Australia; 200324 VIP 5-years Australia; 2003110 BMES-II Brazil; 200327 Review of 74 Cataract projects 1986--1995 India; 2003102

Improving with pinhole to better than 20/60 Improving with pinhole; level of improvement not clear

VI prevalence ranged from 0.63% (persons 40--49 yrs) to 27.3% (among those 80--89 yrs) 14.3%

CVI was the most frequent cause

Improving with subjective refraction from 20/40 or worse

3.0%

Improving with pinhole 1þ line

n 5 4,735; 40þ yrs

17%

13.8%

Improving with refraction 1þ line

n 5 2,522; all ages

Moderate VI: 7.2%

4.2%

Improving with refraction from moderate VI (20/40--20/200) 545

(Continued on the next page)

BMES 5 Blue Mountains eye study; CVI 5 correctable visual impairment; NCVI 5 non-correctable visual impairment; NHANES 5 National health and nutrition examination survey; VA 5 visual acuity; VI 5 visual impairment; VIP 5 visual impairment project; WHO 5 World Health Organization.

2.4% and 2.5% due to CVI (for whites and blacks, respectively). Baltimore; 1990104

n 5 5,300 noninstitutionalized blacks and whites; 40þ yrs

VI prevalence 3.9%; prevalence of blindness 0.6% VI prevalence 3.7% and 4.4% (whites and blacks, respectively) n 5 10,148; all ages Lebanon; 199761

VI prevalence (!20/60) 1.28% Australia; 199799 VIP

London; 199884

n 5 1,547; 65þ yrs

n 5 3,266; 40þ yrs

60% improved 1þ line. The majority improved to 20/40 or better 2.0%

Improving with auto refraction to 20/40 or better VA less than 20/20 assessed by auto refraction and subjective refinement Improving with pinhole from 20/ 60 or worse Improving with refraction or pinhole; level of improvement not specified 9%

Overall 16.4% due to CVI

VI:25.5%. Prevalence of moderate/severe blindness 4.37% 30% n 5 5,342; 50þ yrs China; 199958

Frequency of CVI Frequency of VI Population Region; year

TABLE 2 (Continued)

Improving with pinhole to 0.32 or less

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Definition of ‘‘Correctable’’ Impairment

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In India, a total of 40,447 adults aged 50 years and over had their VA measured.70 Among the examined population, 4.4% (95% confidence interval [CI]: 4.1-4.8) had severe PVI (!6/60--3/60 in the better eye, and 3.6% (95% CI: 3.3--3.9) were blind (vision !3/60 in the better eye, using presenting vision). The prevalence of PVI (!6/18--6/60) was 16.8% (95% CI: 16.0--17.5), and of these, an improvement in vision using pinhole correction was possible in 54.0%.70 In Australia, The Blue Mountains Eye Study (BMES) evaluated the change in VA and prevalence of visual impairment in a population-based community cohort aged 49 years and over.32,33 At both crosssections 1 and 2, approximately two-thirds of visual impairment (!20/40) was correctable by refraction. At cross-section 1, 7.5% of participants had CVI and 3.6% had NCVI. The corresponding figures at crosssection 2 were 5.6% and 2.7% respectively. The Melbourne Visual Impairment Project (VIP)99 reported that 60% of people with visual impairment (!20/60) improved by at least one line with refraction. A later analysis of 13 data clusters from the VIP reported 10% of the total population had CVI and were able to improve one or more lines on refraction.59 An analysis of the combined data sets from both VIP and BMES-I studies (N 5 8,909) was conducted. This revealed prevalence of PVI (!20 / 40) ranged from 0.67% among people aged 40-49 years, up to 39.5% among those aged 90 years and over. Blindness (!20 / 200) ranged from 0% among those 40-49 years, up to 16.9% among those aged 90 years and over. Using the combined samples, it was concluded that 62% of low vision and 4% of blindness in Australia was due to refractive error.98 In summary, CVI has been found to account for a large proportion of visual impairment across the world. In developed countries such as Australia, the UK, and the USA, CVI has been reported to account for between 21%105 and 83%108 of cases of visual impairment. In developing countries, CVI is often reported as the major cause of low vision, responsible for between 19%25 and 81%83 of visual impairment and between 1.6%40 and 35%8 of blindness. B. COURSE OF CORRECTABLE VISUAL IMPAIRMENT OVER TIME

Very few longitudinal studies have assessed the course of CVI over time, and these are limited to Australian, older age (40þ years) samples. These reports suggest that CVI may persist over time for many,32,33 even after people have been informed of the potential for refractive improvement. Apart from one follow-up screening study,81 there have been no longitudinal studies of the course of CVI in children. Preslan and Novak reported a similar

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level of refractive error among pre-kindergarten children in their baseline (8.2%) and one-year follow-up study (7.4%). Of 40 students seen at baseline who were also reviewed at follow-up, only one-third of those needing spectacles were actually wearing them one year later, again suggesting that CVI can persist over time despite its identification. C. FACTORS ASSOCIATED WITH CORRECTABLE VISUAL IMPAIRMENT

Some studies have reported factors associated with visual impairment generally, yet failed to isolate factors specifically related to CVI.21,108 Similarly, some studies have reported types of refractive error in children (i.e., astigmatism, hyperopia, myopia)22,38,42,44,69 rather than factors associated specifically with a lack of refractive correction. For the purpose of this review, only reports that reported specifically on factors associated with CVI are considered, of which 16 were identified. Many studies suggest that particular groups may be at higher risk for CVI, including older, less educated people, and those living alone or in rural areas, as shown in Table 3. 1. Adults Factors associated with CVI were explored in the Australian BMES sample of older community dwelling adults.101 Clinically relevant under-corrected refractive error was defined as an improvement of 2þ lines on the logMAR chart in those with VA !20/ 30. Older age, hyperopia, longer interval from the last eye examination, and living alone were all associated with undercorrected refractive error. In addition, indicators of lower socioeconomic status, such as past occupation as tradesperson or laborer and receipt of a government pension, were significantly associated with undercorrection. Review of two BMES cross-sectional surveys32,33 demonstrated that CVI, defined as visual impairment improving to visual acuity $20/40 on refraction, was associated with many demographic and ocular variables. When comparing those with CVI to those with no impairment at cross-sections 1 and 2 (6 years apart), the mean age of persons with CVI was slightly older. Persons with myopia were more likely to have CVI, and the odds of CVI increased for those living alone, using community support services, being dependent on others, wearing distance glasses, reporting heart disease, and rating their health as only fair or poor.32 Compared to those who no longer had CVI after 5 years, persistent CVI was more frequent in older individuals, women, those living alone, those using community support services, or those who had a history of heart disease.33 However, after adjusting

547

for age and sex, only history of heart disease and age remained significant predictors. Of 4,735 participants aged 40 years or older in the Melbourne VIP,59 10% were identified as having CVI, defined as an improvement of one or more lines with refraction. The likelihood of undercorrection increased 1.8-fold per age decade after 40 years. The following factors were significantly associated with CVI: main language spoken at home (European or Middle Eastern language increased risk by 2.5- and 3.5-fold, respectively), time since last eye examination, absence of distance glasses, and presence of any ocular disease. Type of refractive error and educational level were also significant; persons with hyperopia and tertiary education were less likely to have under-correction. In the 5-year follow-up of the Melbourne VIP involving 2,584 people aged over 40 years, Dimitrov et al24 reported that both the incidence and severity of CVI increased with age. Persons over age 80 were more likely to have CVI and moderate levels of impairment (!20/60--20/200). CVI was the most frequent cause of visual impairment, accounting for 53% of cases. In addition, it was responsible for over half (59%) of the new cases of bilateral visual impairment (!20/40) in the 5-year period. Among elderly Chinese living in Taiwan57 and Singapore,94 older age was again significantly associated with CVI. Lower education levels and the presence of cataract were also significant predictors,94 as well as myopia, and, to a lesser extent, hyperopia.57 Wearing distance glasses and greater education were associated with a lower prevalence of CVI among Singaporean Chinese.57 In developing countries such as Iran,35 TimorLeste,82 and Bangladesh,6 recent studies have similarly revealed low levels of education or illiteracy predict a higher risk of CVI. Persons living in rural areas also have a greater risk.6,17,82 Among Mexican Americans aged 40 years or older, CVI was more likely in older persons, those with lower education or no insurance coverage, and those who had not seen an eye care provider in the previous two years.67 Among elderly persons registered with GP groups in London, Reidy et al84 also reported associations between refractive error, visual impairment, and underprivilege. There are few studies where spectacle dependence after bilateral monofocal intraocular lenses (IOLs) has been described.49,71,113 Javitt et al reported that 40% of patients targeted to receive monofocal IOLs who achieved emmetropia/ very low myopia were dependent on spectacles for distant use.49 In a second study comparing bilateral multifocal with monofocal IOL implantation, Nijkamp et al showed that between 42% and 60% of monofocal patients reported always

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Factors Associated with Correctable Visual Impairment (CVI); Most Recent Articles First Region; year Singapore Malay; 2009 California; 2008106

Population 91

n 5 3,280; 40--80 yrs n 5 6,129; 40þ yrs

CVI Associated with Age; being a woman; short duration of education Age; short duration of education; no health insurance; low annual income and unemployed status Age; myopia; hyperopia

Chinese Taiwan; 200757

n 5 1,361; 65þ yrs

Egypt; 200728 Timor-Leste; 200782 Australia; 200687,88

n 5 5,839; 7--14 yrs n 5 1,414; 40þ yrs n 5 2,353; 11--14 yrs

Iran; 200635 Singapore; 200645 Australia; 200551

n 5 4,353; 5þ yrs n 5 628; 12--16 yrs n 5 1,738; 6 yrs

Low socioeconomic status (trend only) Rural domicile; illiteracy; farming Older children; ethnicity (East Asian or South East Asian); parental education; hyperopia Age; less educated; myopia Lower academic ability; increased time since last checkup Amblyopia; hyperopia; astigmatism

China; 200543

n 5 4,359; 5--15 yrs

Greater VI; less frequent checkups

Bangladesh; 20046 Singaporean Chinese; 200494 Australia; 200324 VIP Australia; 200232,33 BMES

n 5 11,624; 30þ yrs n 5 1,152; 40þ yrs n 5 2,530; 40þ yrs

Illiterate; rural domicile; uneducated; unemployed Age; less education; cataract Incidence and severity increased with age

BMES--I (n 5 3,654) & II (n 5 3,509); 49þ yrs

Mexican American; 200267

n 5 4,774; 40þ yrs

New Delhi; 200268 India; 200117 Australia; 199959 VIP

n 5 6,447; 5--15 yrs n 5 10,293; all ages n 5 4,735; 40þ yrs

Age; history of heart disease; myopiaa; living alonea; using community support servicesa; dependent on othersa; wearing distance glassesa; health rated as poora Age; less educated; lack of insurance cover; not seen eye professional for 2þ yrs Educational attainment of father Rural domicile Age; no distance correction; presence of ocular conditions; Middle Eastern or European speaking

Spectacle wearers Higher education; wearing distance glasses

Parental employment and house ownership Older child; greater VI; higher parental education

Married; higher education

Tertiary education; hyperopia

BMES 5 Blue Mountains eye study; CVI 5 correctable visual impairment; VI 5 visual impairment; VIP 5 visual impairment project; yrs 5 years. No longer statistically significant once age and sex were adjusted for.

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a

Protective Factors

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TABLE 3

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using distance glasses—the figure varied depending on the time after the surgery.71 If emmetropia is targeted, most surgeons would assume that their patient would be dependent on reading glasses for near tasks.113 The same two studies found that 4--11% of these patients were not dependent on reading glasses.49,71 A recent UK study demonstrated that distance-spectacle dependence after bilateral cataract surgery with a mean achieved spherical equivalent of plano is 22.5%, whereas near-spectacle dependence is 95.7%.113 2. Children In studies of children, similar factors were significantly associated with CVI. In Australia, when children with CVI (n 5 45) were compared to all other children in the sample (n 5 2,308), ethnicity, sex, and parent education were significantly associated with CVI.88 Children with CVI in at least one eye (n 5 96) were more likely to be older, and CVI was slightly more common in girls than boys. When compared to children with no visual impairment (n 5 2,077), those with CVI in at least one eye were significantly more likely to be of East Asian or South Asian ethnicity as compared with Caucasian ethnicity.87 In a RESC study conducted in New Delhi,68 the educational attainment of fathers (considered a surrogate indicator of family socioeconomic status) was a determining factor for whether children with refractive error had corrective glasses. Of children aged 7--15 years in Cairo, most with refractive error did not have glasses (57.7%), and CVI was more frequent in families with low socioeconomic status, although this was not statistically significant.28 He et al43 collected data on the parental awareness of vision problems, spectacle use, and frequency of vision checks among children aged 5--15 years in urban China. Parental awareness of vision difficulties in children was associated with older age of the child, higher parent education, and more severe levels of visual impairment. The purchase of spectacles was associated with more severe levels of visual impairment. Undercorrection among those already wearing spectacles was associated with more severe visual impairment and less frequent checks. D. IMPACTS OF CORRECTABLE VISUAL IMPAIRMENT

Little is known about the impact of CVI on children, although refractive errors have been assumed to negatively affect learning, social, and personal development.100 Further, poor academic performance has an impact on choice of occupation and socioeconomic status in adult life.80 As noted in a recent Cochrane Systematic Review report, however, the disadvantage of attending school with

a visual acuity deficit remains to be quantified, and no robust trials are available that have measured the benefits of school vision screening.80 This is a critically important area to address. Many adult studies have reported on the impact of low vision and blindness generally, but have not necessarily isolated CVI from NCVI (due to conditions such as AMD). Although CVI often accounts for the majority of PVI, many studies have shown it has substantially less impact than NCVI. This suggests it may be inappropriate to make inferences from studies assessing the impact of low vision generally, given that the impact of CVI is not necessarily equivalent to that of NCVI. Therefore, in the section addressing adults and the elderly, only studies that specifically assessed the impact of CVI are reviewed. The available studies tend to assess impact at the individual level, for example, in terms of school/ academic performance, vision-specific or healthrelated quality of life (QOL), depression, or the incidence of nursing home placement, as summarized in Tables 4 and 5. Few studies appear to have considered impact at a broader level, in terms of families or communities. Dandona and Dandona suggest that, if the impact from CVI were considered in terms of ‘‘blind person years,’’ it would be double that from cataract, as CVI typically manifests at a younger age.18 1. Impact on Children a. Education and Learning Only four empirical studies assessed the relationship between visual problems and school achievement. Although myopia has received increasing attention for its high prevalence or ‘‘epidemic’’ levels in parts of the world,90,109 three of these studies emphasized the implications of near vision difficulties for learning. Fulk and Goss36 assessed the relationship between refractive status (myopia, hyperopia, or emmetropia) and teacher evaluations of school performance among 276 children (4--15 years) from two schools. Hyperopic children were more likely to perform poorly, with 34% falling into the lowest level of school performance (compared to 14% of children with emmetropia and 12% with myopia). More recently, Williams et al114 screened 1,298 children (aged 8) using fogging tests, conducting ophthalmic assessments on only 105. None of the children tested in this study were on the Learning Support Service list (a national curriculum-based tool applied to children performing below the national average) or were receiving support for a specific learning disability such as dyslexia. School test

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TABLE 4

Impacts of Correctable Visual Impairment (CVI) in Children Impact Measured

Country; year 36

Teacher evaluations of academic performance

USA; 2001

Stanford test scores

USA; 2006107

Academic performance (math and reading)

USA; 200175

Progression of myopia

Malaysia; 200212

Progression of myopia

Israel; 20063

Self-reported visual function

Mexico; 200729

Self-reported visual function

China; 200814

Visual morbidity

China; 2009119

Bicycle-related injuries

China; 2009

118

Findings n 5 276 children aged 4--15 years in two schools screened; 34% of children with hyperopia, 14% of those with emmetropia, and 12% of children with myopia fell into the lower 25% of school performance, namely, those with hyperopia were more likely to perform poorly Visual symptoms in quality of life questionnaire were inversely related to test scores; the lower the academic score the more vision symptoms were reported Majority of visual problems found related to near vision (e.g., hyperopia) and this was associated with lower test scores; treatments (glasses or visual training) correlated with improvements in grades n 5 47 children aged 9--14 years were blurred by þ0.75 D (6/12) and as a result had more rapid progression of myopia and axial elongation over period of 2 years than those students fully corrected n 5 48 children aged 6--15 were randomly assigned to fully corrected or under-corrected groups (þ0.50 D) and followed over 18 months. Under correction produced slight, but not statistically significant, increase in myopic progression n 5 88 (mean age 12  1.9 yrs); significant improvements in the following subscales of the Refractive Status Vision Profile were seen for the group as a whole after the provision of free spectacles: function, 11.2 points (p 5 0.0001); symptoms, 14.3 points (p ! 0.0001); total score, 10.3 points (p 5 0.0001) n 5 1,892 children aged 11.4--17.1 years were screened for refractive error and visual disability. Children with refractive error $--0.5 D (n 5 185) had a mean self-reported visual function of 82.6  13.9 which declined monotonically to 57.6  15.5 for children with myopia ! --5.5D (n 5 59) n 5 3,226. Refractive error and spectacle power were assessed for 588 (80.2%) children (mean age 5 15.0  1.6 years). Children with inaccurate glasses ($1 D) had presenting vision in the better eye significantly (p ! 0.001) worse than that of children with accurate glasses and 30.3% had presenting acuity # 20/40 Refractive and accident data were available for 1,539 participants (mean age 14.6 yrs). Baseline visual acuity worse than 20/60 in better-seeing eye was not associated with reporting a bicycle accident in the past 3 years

scores were found to be lower for children with refractive errors, with a high proportion (29%) of children with hyperopia having been referred to an educational psychologist. In a quasi-experimental intervention study,75 an association between vision and academic performance was found among inner-city children from low-income families. Although the statistical power of the study was limited, results showed a high level of hyperopia and poor eye movement control among children in grades 0 (kindergarten) through 5. From 801 children screened and 226 undergoing more comprehensive assessments, those identified to receive glasses (n 5 201) and/or vision therapy for convergence; accommodative, oculomotor, and binocular problems; strabismus; or amblyopia (n 5 79) had lower test scores in mathematics and reading relative to the comparison group. However, there are two noteworthy limitations to this study.

First, in their analyses the authors did not adjust for important confounding variables such as neurological impairment or developmental delays. Second, when assessing improvements in performance after provision of reading glasses and vision therapy, a control group was not included for comparison. One small study107 (n 5 91, single school) assessed the association of self-reported visual symptoms and academic performance among children in grades 3, 5, and 7. The short version of the College of Optometrists Vision Development Quality of Life questionnaire was used to assess a range of visual symptoms including, for example, headaches, words running together, difficulty copying from a chalkboard, holding reading material close. Visual symptoms were reported to be inversely related to academic performance, and symptoms reported by parents were more strongly associated with low academic performance than those reported by students. However, the smaller sample size

551

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(particularly as there were only 13 seventh graders) may have reduced the power to observe any significant differences. It needs to be emphasized that these conclusions resulting from the four studies on the relationship between vision and education must be interpreted with caution, as the data are not robust and have several scientific limitations. Primarily, the educational difficulties reported by the authors may be due to factors other than refractive error (home environment, IQ, etc.); however, the large majority of these studies have not adequately adjusted for other potential confounding variables. Second, these reports in children include quite small sample sizes, which may have influenced their statistical power and subsequent analyses. Finally, the studies reporting on the positive results of vision therapy did not include appropriate control groups for comparison, and more often than not, the group receiving vision therapy treatment or glasses were not representative of the general population. b. Visual Outcomes A further impact of refractive errors in children is a potential effect of undercorrection on progression of visual conditions. Two small prospective experimental studies identified a trend toward undercorrection of myopia increasing, rather than inhibiting, myopia progression.3,12 2. Impact on Adults or Elderly Persons a. Vision-specific Quality of Life Many studies assessing quality of life have used the National Eye Institute Visual Function Questionnaire (NEI-VFQ), a 25-item vision-specific quality of life instrument developed in the USA. Using this instrument, a small measurable impact of CVI has been found in various cross-sectional studies. The Proyecto VER study of Mexican Americans (n 5 4,774) found that persons with CVI were more likely to report difficulties with nine of the NEI-VFQ subscales compared to those without CVI. However, no analysis was conducted comparing the impacts from CVI to those from NCVI.67 Among 1,174 residents aged over 49 years identified as part of the BMES extension project in Australia,10 scores on eight dimensions of the NEI-VFQ were significantly affected by CVI when compared to those with no visual impairment. These included general vision, near vision, distance vision, mental health, role difficulty, dependency, peripheral vision, and the composite score. The impact from CVI, although measurable, was considerably milder than that from NCVI. Compared to persons both with CVI and with no visual impairment, NCVI had a significantly more

dramatic negative impact on all 12 subscale scores as well as the composite score. Other studies7,67 have similarly reported significantly lower scores on several of the NEI-VFQ dimensions among persons with CVI compared to those with no impairment. Broman et al7 noted that the CVI decrements were comparable to that found among participants with cataract, but persons with diabetic retinopathy and glaucoma reported greater decreases in 8 out of 12 subscales, again suggesting more extensive impact from NCVI. A cross-sectional study in India using a different measure found that cataract, glaucoma, and refractive error were all associated with quality of life and visual function, but when visual acuity was added to the model, refractive error changed to higher scores.72 A singlecenter randomized controlled trial among community dwelling elders found that persons who received a voucher for free spectacles and/or a magnifier immediately after screening (n 5 66) experienced greater improvement in selected NEI-VFQ subscale scores than those allocated to a delayed treatment group (n 5 65).13 Subscales where improvements were found included general vision, distance and near acuities, and mental health. Thus, correcting refractive error may improve particular aspects of vision-related quality of life. b. Health-related Quality of Life and Depression Significant differences in the limited dimensions of the generic Short-Form-36 Health Survey (SF-36) health related QOL scores have been reported between persons with no visual impairment and those with CVI in cross-sectional studies. For example, among 1,361 Chinese from Taiwan, a significantly lower score was reported by those with CVI in the dimension of physical functioning, but no significant association was found in relation to the other seven scale dimensions.57 The authors cautioned that, due to the limitations of a cross-sectional design, it is plausible that poor physical functioning could have led to CVI because of difficulty accessing eye services. Among BMES-II participants (n 5 3,154), CVI had a statistically significant impact on three QOL dimensions, specifically physical functioning, social functioning, and the physical component score.11 This impact, however, was a much lower one than that found among persons with NCVI, for whom scores in vitality, mental health, and the mental component scores were substantially lower than for CVI. The impact of NCVI was considerably more extensive compared to persons without visual impairment, with significantly lower scores reported in physical functioning, general health, vitality, social functioning, mental health, and the mental component score.

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A randomized controlled trial of nursing home residents in Birmingham76 reported that participants receiving immediate refractive correction (as opposed to those in a delayed correction group) scored higher in QOL, vision activities of daily living, and lower on depressive symptoms (15-item Geriatric Depression Scale). Using the Nursing Home Vision-Targeted Health Related Quality of Life Questionnaire, following adjustment for baseline values, significant improvements were reported after immediate refractive correction in five of nine subscales (general vision, reading, psychological distress, activities and hobbies, and social interaction). No significant differences were found between the groups when the generic SF-36 measure was used.76 The only study to date to report no association at all between decreased QOL and CVI was the Andhra Pradesh Eye Disease Study conducted in India among adults aged 40 years and older.74 This study, however, used the WHO QOL instrument, and the non-significant results could be attributable to the use of a different QOL assessment. Nevertheless, persons with cataract, retinal disease, glaucoma, and corneal disease did demonstrate significantly lower scores using this instrument, compared to those without visual impairment. This again suggests that CVI has a considerably lower impact than NCVI, and that its deleterious impacts are yet to be convincingly or clearly demonstrated. c. Nursing Home Placement Wang et al110 assessed the incidence of nursing home placement over 6 years among a populationbased cohort of Australians (BMES) aged 49 years and older and reported that the age-adjusted incidence was greatest among people with NCVI (16.2%), but persons with CVI had some increase in incidence compared to those with no visual impairment (8.1% vs 3.6%). After adjusting for multiple predisposing, enabling and need factors, as well as health risk behaviors, persons with both CVI and NCVI had a relatively similar increased risk of nursing home admission within the time period studied, approximately double that of people with normal vision at baseline. A potentially confounding issue here is that CVI may reflect a reduced level of independence and ability to go out, which itself is a predictor of nursing home placement. d. Productivity An experimental study23 using a double-masked placebo-controlled randomized design found miscorrected astigmatic refractive error had a negative impact on productivity among young adult computer

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users (aged 19--30 years). Compared to workers receiving correction for astigmatism, those who were miscorrected by 2.0 diopters experienced more discomfort and reduced speed and accuracy on tasks. Using these results, Daum et al conclude a favorable cost--benefit ratio of at least 2.3 for the visual correction of employees.

IV. Discussion A. WHY IS CORRECTABLE VISUAL IMPAIRMENT SO PREVALENT?

Very few of the larger studies that report CVI prevalence have assessed barriers to the utilization of eye services or spectacle ownership or wear among those with CVI. Additional literature searches were undertaken using barriers as a key word. These revealed several studies exploring reasons for the low use of spectacles and /or infrequent use of eye health care services generally (see Table 6). These articles suggest that barriers may exist at three levels: the social level, in relation to the treatment or service context, and at an individual level. 1. Social Barriers CVI has been associated with indicators of lower socioeconomic status. Correspondingly, financial considerations have often been identified as a primary reason for non-attendance to eye care services or for failure to purchase spectacles.20,31,46,82,116 Predictably, studies in developing communities have demonstrated a greater influence of economic factors on CVI. In a cross-sectional survey in Timor-Leste, 96% of participants who needed spectacles were willing to wear them, but around half were not willing to pay a cost of US$1.82 Economic reasons were also identified among 30% of people who failed to seek treatment or to attend routine appointments in India.20 Among people who had discontinued using spectacles, reasons given included loss and being unable to afford a new pair.19 Among reasons for nonattendance at an eye camp in India, both direct and indirect costs were cited.31 In a Pakistan community, affordability was given as a major reason for not purchasing spectacles.116 In more affluent societies, this association appears to be only marginally weaker. In 1993, a US National Access to Care survey (n 5 3,480) was conducted as a follow-up component to the 1993 National Health Interview Survey. Financial reasons were cited as a primary barrier by 80% of people who reported an unmet need for spectacles.46 Even when spectacles have been provided free of charge, however, the uptake has reportedly been low, though higher than when only a prescription was given.75,111

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UNCORRECTED REFRACTIVE ERROR TABLE 5

Impacts of Correctable Visual Impairment (CVI) in Adults and Elderly Impact Measured Vision specific QOL; NEI-VFQ-25 scale

Country; year Australia BMES extension; 200610

Mexican American; 20027

Mexican American; 200267

California; 200613

Vision targeted health related QOL; VF 14; depressive symptoms (GDS) SF-36 health related quality of life

USA; 200776

Australia BMES-II; 200411

Chinese Taiwan; 200757 QOL-WHO

India; 200674

QOL questionnaire

India; 200572

Mortality

Australia; BMES; 200952

Findings Cross-sectional analysis. Measurable impact from CVI; but much less than that from NCVI. CVI affected 8 dimensions: general vision; near vision; distance vision; mental health; role difficulty; dependency; peripheral vision; and the composite score. NCVI had significantly greater impact in all subscales relative to those with no VI and CVI. Cross-sectional analysis. Those with CVI had lower scores than those without in: general vision, near vision, distance vision, driving, ocular pain, role difficulties, dependency, social functioning, and mental health (not significant in general health, peripheral vision, or color vision). Those with CVI reported decrements in QOL comparable to those reported by participants with cataract. Those with diabetic retinopathy and glaucoma reported larger decreases in scores than those with cataract or CVI. Cross-sectional analysis. Those with CVI were more likely to report difficulties with general vision, near vision, distance vision and driving, role difficulties, dependency, impeded social functioning, and impaired mental health. Cross-sectional analysis. Those receiving prescription and voucher for free glasses had greater improvements than those allocated to an intention-to-treat (delay intervention) group in terms of: general vision, near and distance vision, and the mental component score. Note 14.8% did not obtain new glasses before the follow-up despite the fact they were free. Intervention study. Those randomized to receive immediate refractive correction vs the delayed correction group had better scores on QOL and VF; and lower scores on depression. Cross-sectional analysis. CVI had less impact than NCVI but some impact compared to no VI. CVI vs no VI: significantly lower scores in physical functioning, social functioning, and physical component scores. NCVI vs CVI: significantly lower scores in vitality, mental health, and mental component score. Cross-sectional analysis. Persons without VI v. those with CVI: difference in the physical functioning dimension but none of the other seven dimensions. Cross-sectional analysis. Refractive errors were not associated with QOL score (i.e., CVI had no significant effect on QOL). Persons with cataract, retinal disease, glaucoma, and corneal disease had lower scores than those with no VI. When visual acuity was added to the model, these were no longer significantly lower for cataract and retinal disease. Cross-sectional analysis. Age, education, occupation, cataract, glaucoma, refractive error, and VA were all associated with QOL and visual function scores. Scores were lower in models without VA. When VA was added, refractive error changed to higher scores suggesting improvements may be obtained after refractive correction as a function of VA. Compared to persons without any VI, persons with CVI had a 26% increased risk of all-cause mortality,; multivariateadjusted hazard ratios HR 5 1.26 (95% CI 1.04--1.53). CVI also increase risk mortality risk via indirect pathways involving disability in walking and poor self-rated health. (Continued on next page)

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TABLE 5 (Continued ) Impact Measured

Country; year

Incidence of NH placement over 6 yrs

Australia BMES; 2003

Comfort and productivity

USA; 200423

Blind person-years

India; 200118

Economic productivity

Review of WHO sub -regions; 200997

Findings 110

Age standardized incidence of NH placement: Persons with NCVI, 16.2%; with CVI, 8.1%; with no impairment, 3.6%. Multivariate-adjusted risk ratios similar for persons with VI and those with CVI (1.8, 2.1). Intervention study. Some workers (19--30 years) were corrected and others mis-corrected for astigmatism. Those with refractive error produced more errors in tasks set; took more time and experienced more discomfort. Authors report that CVI accounts for more than twice the number of blind person-years compared with cataract over the lifetime of those currently blind because it manifests at a younger age. The total global productivity loss (in international dollars, I$) associated with the burden of CVI was I$ 427.7 billion before, and I$ 268.8 billion after, adjustment by labor force participation rate and employment rate.

BMES 5 Blue Mountains eye study; GDS 5 geriatric depression scale; NCVI 5 non-correctable visual impairment; NH 5 nursing home; QOL 5 quality of life; VA 5 visual acuity; VI 5 visual impairment; VF 5 visual function; WHO 5 World Health Organization.

Other social factors impacting on participation in eye care include, for example, high dependency and isolation, which can interfere with ability to attend clinics.33 Family responsibilities, difficulties planning ahead,31,56 inability to leave work, and lack of child care39 are reported by adults as challenges to participation in eye health care. Inadequate screening and lack of community awareness of the importance of vision checks is another factor identified in focus groups with parents.117 Preslan and Novak81 speculated that a lack of continuity of eye care and concomitant parent education were responsible for poor levels of spectacle uptake (30%) after student screening. In addition, some studies have shown that poor spectacle uptake can relate to issues like embarrassment, cosmesis,82 pressure, social stigma, and teasing.9,116,117 2. Treatment- / Service-related Barriers As noted previously, a number of studies have revealed associations between rural domicile and CVI, perhaps reflecting accessibility issues raised in research on barriers to eye health.39,117 Particularly in developing countries where optical services remain limited, the accessibility of services in terms of numbers of eye clinics or trained professionals available poses a considerable barrier to the elimination of avoidable visual impairment and blindness.5,18,86 Even in economically advanced countries such as Australia, the accessibility of services can vary considerably between states and across rural, urban, and remote areas. Schlenther et al95 noted that among Aboriginal people, physical access to services, limited services, and long travel distances remain barriers. Among participants in the VIP, ophthalmology

services were utilized at lower rates in rural areas.53 A 1996 Australian Medical Workforce Advisory Committee reportA noted that most ophthalmologists were located in the populated eastern Australian states, with over 75% practicing in capital cities. Similarly, capital cities were well serviced, but rural and remote areas generally had no optometrists.55 These concerns about workforce adequacy and distribution in Australia are exacerbated by the aging of the eye health workforceA,B and the anticipated increased demand for eye services with population aging. The Eye Health in Australia ReportC predicts a doubling of persons aged over 55 years between 2002 and 2032. Even when services are available, minority groups have difficulties in their use. For example, Schlenther et al95 argued that Australian Aboriginal people experienced long waiting times and perceive that staff are unfriendly and lack understanding of their cultural values. In focus groups and interviews with Indians living in London, service-level barriers such as difficulties in patient doctor relationships in primary care, delays in access to specialist eye care, long waiting lists at the hospital level, and poor communication were reported.78 Eighty-seven percent (87%) of elderly patients visiting hospital accident and emergency services in London reported their vision had never been checked by their doctor.85 This suggests health professionals themselves may have poor recognition of vision screening as a health priority for older patients. Further treatment-related barriers, such as the cost of testing or of corrective lenses, may contribute to a lack of spectacle wear.26,31,42,46,85,86,116,117 The inconvenience of spectacle use may pose an additional barrier. Among children aged 5--18 years, headache attributed to spectacle wearing was one

555

UNCORRECTED REFRACTIVE ERROR TABLE 6

Studies Reporting Barriers to Eye Care and/or Spectacle Wear in Adults And Children Study Description

Barriers Identified 4

Focus groups, USA; 2003 Focus groups and interviews with Indian population in London; elders and GPs; 200678

Cross sectional survey of CVI; including presbyopia, Timor-Leste; 200782 Study of the utilization of eye care services in India; 200020 Elderly attending accident and emergency, UK; 199385 Focus groups; interviews and 479 questionnaires in Pakistan; 2007116 Population study in India; 200219

Fiji survey of households and semi structured interviews; 200626 Eye camp in India; focus groups and interviews; 199931 Barriers to eye care among Hispanics with diabetes; 200439 National Access to Care Survey; n 5 3,480; USA 199946 Rural teenagers from China; 200742 Interviews with parents, USA; 200656 Focus groups, USA; 1998117

Spectacle wear compliance among 5--18-yr-olds in Mexico; n 5 493; 20069

Panel survey of 6--18-yr-olds in USA; 200454

Problems with reading; adjusting between near and far vision; appearance Misconceptions about sight loss, causes, and treatments; influence of background and fear on behaviour; experiences and perceptions about healthcare services; attitudinal barriers showing health is not a priority and elderly are resigned to fate of poor vision.; difficulties in patient doctor relationship in primary care and delay in specialist care; dissatisfaction at hospital level due to long waiting lists and poor communication Found 96% of the sample willing to wear spectacles but many (around half) were unwilling to pay US$1; those unwilling to wear spectacles reported reasons of cosmesis and embarrassment Those with refractive error were less likely to notice decrease in vision; only 41% sought treatment; reasons reported were personal (49.5%), economic (30.8%), social (8.4%) 87% said their doctor had never checked their vision; half not been to optician within the last 2 years; money, perception of not being necessary, and mobility were reasons given Many did not understand refractive error services were offered and did not consider themselves to have refractive error; reasons for not purchasing: affordability, cosmetic factors, stigma, social pressure in terms of appearance, and perception children may inherit impairment; many thought glasses would cause vision to deteriorate 13.8% of sample had refractive error, current use of spectacles was 34.2%, previous use 12.3%; odds of using spectacles higher for persons with education, living in urban areas, or with aphakia/ pseudophakia; among persons who had discontinued use, reasons given were: felt prescription given not correct, uncomfortable, lost, and unable to afford new glasses Only 66% of household members with previous eye problems had consulted eye care services and lower in older people; reasons given for not seeking care included: fatalistic attitude (did not bother, can manage, and accepted condition), expense, and fear Reasons given for not attending eye camp included: fear (of eye damage), cost (direct and indirect), family responsibilities, ageism, fatalism and attitude of being able to cope Barriers included financial concerns, lack of transportation, clinic too far away, inability to leave work, physician not speaking Spanish, lack of child care; only half had received written material on diabetic retinopathy from physician More than 5% reported unmet need for eye glasses and 80% cited financial reasons; those in poor health and blacks were more likely to face barriers Barriers to use of glasses included parental awareness of visual problem, attitudes regarding wear of glasses, cost, concerns glasses may progress refractive error Reasons for no follow-up after screening: family issues, parental perceptions of visual problems, and difficulty planning ahead were significant factors Barriers to follow-up: lack of community awareness about frequency and effect of refractive errors, parental perception of inadequate communication between schools and parents and community, high cost of corrective lenses, limited availability of eye care appointments, adolescent reluctance to wear glasses. Only 13.4% were wearing glasses; 34% had glasses but were not wearing them.; spectacle wear was higher in rural areas and lower among older children; reasons for non-wearing included: forgot, concerned about appearance, use at special times only, broken or lost, feel not needed, cause headache, parents disapprove.; those older and in urban areas significantly more likely to be concerned re: appearance/being teased 25% had corrective lenses; less likely in elementary school, boys, Hispanic and Hispanic black, those below poverty level, those with public insurance (as opposed to private) (Continued on next page)

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TABLE 6 (Continued ) Study Description Screening and provision of glasses; Tanzania; 2008111 Population study (VIP) of eye care service utilization, Australia; 200253

Barriers Identified Those with spectacles provided free were more likely to be wearing glasses 3 months later than those given prescription; generally low CVI prevalence and low uptake of spectacles Majority of those noticing change in vision had seen an eye care provider; of the 9% who had not, reasons given included: change not severe enough, too busy, belief it was normal for eyesight to deteriorate with age

CVI 5 correctable visual impairment; GP 5 geriatric patients; VIP 5 visual impairment project.

reason for not wearing them.9 During the development of a refractive correction quality of life measure, Berry et al4 reported that problems with reading or near--far vision adjustment could impair quality of life with spectacles, along with concerns about appearance. 3. Individual Barriers Individual’s attitudes may be a barrier to eye care service utilization or spectacle use, such as fatalism and a feeling of being able to cope despite visual impairment.26,31,53 Obviously, how vision, vision loss, and spectacles are perceived impact behavior. Some may be unaware of their need for spectacles, may consider spectacles unnecessary, or may not prioritize vision in the context of other health problems or life choices.20,24,53 In a study of eye care service utilization in India, people with refractive error were less likely to notice a decrease in vision than those with other forms of visual impairment.20 Focus groups, interviews and questionnaires undertaken in a Pakistan community similarly found that many participants did not consider they had a refractive error.116 In some studies the degree of improvement used to define CVI is minimal, sometimes only one line on an eye chart,24 and people may quite reasonably believe correction is not warranted for such modest gain. This highlights the need to standardize definitions for reporting. Among an Indian population living in London, misperceptions and fears about sight loss and its causes and treatments were barriers.78 Teenagers in China were found to hold misperceptions about their vision, believing that wearing glasses actually worsens refractive error.42 Parents’ attitudes toward and awareness of visual problems are another barrier to children’s eye care.9,42,56

V. Conclusions and Implications The contribution of CVI to low vision and blindness throughout the world has been increasingly documented over recent years. Although a growing number of studies document the prevalence of CVI, different definitions and measures of visual

impairment, blindness, and CVI—along with varied methods of communicating these findings—limits meaningful comparisons. There is an urgent need to standardize definitions. Despite these limitations, the available evidence demonstrates the important contribution of refractive error to visual impairment in both developed and developing countries. CVI has been identified as a major cause of mild to moderate levels of visual impairment, together with cataract, both of which are eminently treatable. CVI as a cause of blindness is more frequent in developing than developed countries. Many studies have identified factors associated with low vision generally rather than specifically with CVI. A modest body of evidence that would benefit from confirmation in further studies has identified several factors associated with CVI. Risk groups include the elderly, less well-educated persons, and those living alone or in rural areas. As most studies have had a cross-sectional rather than longitudinal design, improved knowledge of changes in CVI over time represents one aspect needing further investigation. There is also a need for research to assess the effectiveness of different interventions on CVI, particularly addressing their impact on general health and independent living. Although a considerable number of studies have reported CVI prevalence, we must develop more rigorous research designs permitting investigation of underlying risk factors and impacts of CVI, especially the latter. Most existing studies report a much lower impact from CVI than NCVI. Nonetheless, in a few studies impacts have been measured from CVI on selected dimensions of vision specific and generic quality of life instruments, on depression, the likelihood or need for institutionalization, and on productivity, but more are needed. In children, some links have been made between refractive error and poor educational performance and between undercorrection and progression of myopia, but further study is urgently needed to supplement the paucity of evidence regarding the potential harmful effects of CVI. As noted by Dandona and Dandona,18 systematic data on barriers to refractive correction remain scant.

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The wider literature on barriers to eye healthcare suggests that these exist across three inter-related levels: at the level of individuals, within the service or treatment context, and at a societal level. Given the high frequency of CVI, the adequacy of current policy and practice in recognizing and addressing this condition could be questioned, but before greater effort and funding can be justifiably re-directed to CVI, much more research is required to quantify its nature, course, and particularly its impacts. Given the WHO and IAPB recognition of CVI (as ‘‘uncorrected refractive error’’) within the Vision2020 quest to prevent avoidable blindness and visual impairment, quantifying the impacts of CVI assumes a high priority.

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Other Cited Material

A. Australian Medical Workforce Advisory Committee. The Ophthalmology Workforce in Australia. AMWAC Report 1996.6. Sydney. 1996 B. Australian Bureau of Statistics. 4819.0 Selected Health Occupations Australia, 2006. 2008 C. Commonwealth of Australia. Eye Health in Australia—A background paper to the National Framework for Action to Promote Eye Health and Prevent Avoidable Blindness and Vision Loss. 2005 The authors reported no proprietary or commercial interest in any production mentioned or concept discussed in this article. Reprint address: Professor Paul Mitchell, Eye Clinic (B4A), Westmead Hospital, Hawkesbury Road, Westmead, NSW 2145, Australia. e-mail: [email protected].

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Outline I. Introduction A. The emergence of ‘correctable’ visual impairment as a global health challenge II. Methods A. Literature search strategy B. Important methodological issues identified III. Findings A. Frequency of correctable visual impairment 1. Studies that included only children 2. Studies that included both children and adults 3. Studies that included only adults B. Course of correctable visual impairment over time C. Factors associated with correctable visual impairment 1. Adults 2. Children

D. Impacts of correctable visual impairment 1. Impact on children a. Education and learning b. Visual outcomes 2. Impact on adults or elderly persons a. Vision-specific quality of life b. Health-related quality of life and depression c. Nursing home placement d. Productivity IV. Discussion A. Why is correctable visual impairment so prevalent? 1. Social barriers 2. Treatment- / service-related barriers 3. Individual barriers V. Conclusions and implications