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Clinical and Epidemiologic Research  |   March 2013
How Much Eye Care Services Do Asian Populations Need? Projection from the Singapore Epidemiology of Eye Disease (SEED) Study
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; the
  • Ching-Yu Cheng
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; the
    Department of Ophthalmology, Yong Loo Lin School of Medicine, and the
    Saw Swee Hock School of Public Health, National University of Singapore, Singapore; the
  • Ecosse L. Lamoureux
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; the
    Centre for Eye Research Australia, University of Melbourne, Melbourne, Australia;
  • Peggy P. C. Chiang
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; the
    Duke-National University of Singapore Graduate Medical School, Singapore; the
  • 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; and the
  • Jie Jin Wang
    Centre for Eye Research Australia, University of Melbourne, Melbourne, Australia;
    Centre for Vision Research, University of Sydney, Sydney, Australia.
  • Paul Mitchell
    Centre for Vision Research, University of Sydney, Sydney, Australia.
  • Seang-Mei Saw
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; the
    Department of Ophthalmology, Yong Loo Lin School of Medicine, and the
    Saw Swee Hock School of Public Health, National University of Singapore, Singapore; the
  • Tien Y. Wong
    From the Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; the
    Department of Ophthalmology, Yong Loo Lin School of Medicine, and the
  • Corresponding author: Tien Y. Wong, Singapore Eye Research Institute, 11 Third Hospital Avenue, #05-00, Singapore 168751; ophwty@nus.edu.sg
Investigative Ophthalmology & Visual Science March 2013, Vol.54, 2171-2177. doi:10.1167/iovs.12-11393
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      Yingfeng Zheng, Ching-Yu Cheng, Ecosse L. Lamoureux, Peggy P. C. Chiang, Ainur Rahman Anuar, Jie Jin Wang, Paul Mitchell, Seang-Mei Saw, Tien Y. Wong; How Much Eye Care Services Do Asian Populations Need? Projection from the Singapore Epidemiology of Eye Disease (SEED) Study. Invest. Ophthalmol. Vis. Sci. 2013;54(3):2171-2177. doi: 10.1167/iovs.12-11393.

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Abstract

Purpose.: We quantified and measured the needs for specific eye care services, including refractive services (RS), annual eye examination services (AES), cataract surgery services (CSS), and low vision services (LVS) in urban adult populations in Asia.

Methods.: We conducted three population-based studies of Singapore-resident Chinese, Malays, and Indians aged ≥40 years to measure the proportion of people who needed specific eye care services.

Results.: Our data included 3353 Chinese, 3280 Malays, and 3400 Indians (participation rate 73.6%). Overall, approximately 70% of the populations needed eye care services and more than 30% had more than one need. The age-standardized proportion of people who need RS, AES, CSS, and LVS were 65.3%, 22.4%, 12.5%, and 0.5%, respectively, in Chinese. These figures were 49.6%, 33.6%, 11.0%, and 0.7%, respectively, in Malays, and 55.6%, 40.0%, 13.4%, and 0.8%, respectively, in Indians. With demographic change, our projection showed that the number of adults needing eye care services in urban Asia will grow from 437 million in 2010 to 827 million in 2030. Diabetes was a major cause of AES and a significant predictor for CSS, whereas higher blood pressure was a predictor for AES.

Conclusions.: The needs for eye care services in an urban setting in Asia is high, particularly the needs for RS, AES, and CSS. The high prevalences of diabetes and hypertension are the driving factors underlying these needs. The burden of providing such eye care services highlights the need for new strategies for improvements in primary care and capacity building for eye care professionals other than ophthalmologists.

Introduction
The planning of eye care services requires accurate measurements of prevalence and causes of visual impairment (VI). According to the World Health Organization (WHO) criterion, best-corrected VI is defined as best-corrected visual acuity (BCVA) < 6/18. 1 Additionally, recent epidemiologic surveys have used the concept “presenting VI” (PVI, based on “presenting” vision, i.e., visual acuity [VA] obtained through current available refractive correction) to reflect the influence of uncorrected refractive error on daily activities. 1 However, the traditional definition of VI, whether BCVA or PVI, only represents a summary metric and does not reflect the entire spectrum of needs for specific eye care services, such as need for cataract surgery, refractive correction, low vision rehabilitation, and annual dilated eye examination services, in the general population. 
There have been wide variations in the extent and pattern of need for eye care services among different geographic regions, due to discrepancies and changes in economic development, ageing of populations, rising epidemic of chronic systematic illness, and specific ethnic practices and influences worldwide. 25 Importantly, in Asia, home to half of the world's population, there are significant demographic, economic, and social changes, and thus it is critical to understand the current and projected needs for eye care services in Asia. Such information allows for strategic planning for the development of appropriate eye health care resources and health policies to better meet future eye care demands in the population. 
We present a practical framework to assess the needs for refractive services (RS), annual eye examination services (AES), cataract surgery services (CSS), and low vision services (LVS) in a multi-ethnic Asian population residing in Singapore. Using this framework, we projected conservatively the number of people who need such services in Asia. 
Methods
Study Population
The Singapore Epidemiology of Eye Disease (SEED) Study is a population-based, cross-sectional study of 3353 Chinese, 3280 Malays, and 3400 Indian adults aged 40 and older. 6,7 The study was conducted in southwestern Singapore between 2004 and 2011. 8,9 Using an age-stratified random sampling strategy, 6752 Chinese names, 5600 Malay names, and 6350 Indian names were selected from the Ministry of Home Affairs, and 4605 Chinese, 4168 Malays, and 4497 Indians were deemed eligible to participate. The “ineligible” persons were those who had moved from the residential address, had not lived there in the past six months, or were deceased or terminally ill. A total of 3353 Chinese, 3280 Malays, and 3400 Indians participated in our study, giving response rates of 72.8%, 78.7%, and 75.6%, respectively. In each ethnic cohort, nonparticipants on average were slightly older than participants (P < 0.001), but there was no significant sex difference. The study adhered to the Declaration of Helsinki, and ethics approval was obtained from the Singapore Eye Research Institute (SERI) Institutional Review Board. All examinations were done at SERI. A detailed interviewer-administered questionnaire was used to collect information regarding socioeconomic status (e.g., education, income, and housing type) and medical history of eye diseases. 
VA Testing
Presenting monocular VA (PVA) was measured separately using a logarithm of the minimum angle of resolution (logMAR) chart (Lighthouse International, New York, NY) at a distance of 4 m and recorded as the smallest line read with one or no errors. BCVA was measured by certified study optometrists after correcting for refractive errors. When no number on the chart could be read at 4 m, the participant was instructed to move to 3, 2, or 1 m, consecutively. When no number could be read at all, VA was recorded as counting fingers (CF), hand movements (HM), perception of light (PL), or no perception of light (NPL). 
Definitions of Needs for Specific Eye Care Services
Definition of Need for RS.
Participants who needed RS included persons who had “met” or “unmet” RS need. Participants with “unmet RS need” were defined as those with VA < 20/40, or logMAR > 0.3, in either eye before refraction that improved after refraction to no impairment (to 20/40), but had not had spectacles, or had undercorrected spectacles or prescription. Participants who “met RS need” were defined as those whose unaided VA improved from poorer than 20/40 to ≥20/40 using participants' own spectacles. Our main analyses focused on the need for RS (a combination of “met” and “unmet” RS need) unless otherwise stated. To address the impact of unilateral disease, our definition of RS was based on the data in “either eye” instead of the “better-seeing eye.” 
Definition of Need for CSS.
Participants who needed CSS included persons who had “met” or “unmet” CSS need. Participants with “unmet CSS need” were those with substantial cataract as the major cause of VI in either eye in which there was no evidence of retinal abnormality that otherwise explained the vision loss. Participants who “met CSS need” were those with pseudophakia/aphakia in either eye. Our main analyses focused on the need for CSS (a combination of “met” and “unmet” CSS need) unless otherwise stated. To address the impact of unilateral disease, our definition of CSS was based on the data in “either eye” instead of the “better-seeing eye.” 
Definition of Need for Annual (or More Frequent) Eye Examination Services (AES).
The traditional definition of VI only focuses on individuals with poor vision 1 and does not consider persons at risk of vision loss (the high risk group or “preVI”). In response to this, we introduced the term need for AES to reflect the need for regular eye examination for persons at high risk of VI developing in addition to those who already had VI. To be classified as being in need of AES, individuals had to have at least one chronic systemic or eye condition that may result in VI and are required to have regular eye care provision over a long term or lifetime. The chronic conditions include diabetes, glaucoma, glaucoma risk factors, and other major corneal, retinal, or optic nerve diseases (e.g., age-related macular degeneration [AMD], myopic retinopathy, retinal vein occlusion, retinal detachment, macular hole, and anterior ischemic optic neuropathy). This definition excludes causes (e.g., cataract, refractive error) that can be cured by once-off intervention or operation. The definition of AES takes into consideration the American Academy of Ophthalmology Preferred Practice Pattern (AAO-PPP) for comprehensive medical eye examination, which recommends yearly or more frequent eye examination for those who have diabetes mellitus, or who are aged ≥60 years in conjunction with risk factors (e.g., elevated intraocular pressure) for glaucoma. 10  
Diabetes was defined as self-report of a previous diagnosis of the disease by a doctor, use of diabetic medication, or hemoglobin A1c (HbA1c) of 6.5% or greater (as recommended by the American Diabetes Association). 11 Diabetic retinopathy was graded from retinal photographs based on a modification of the Arlie House classification system for the Early Treatment Diabetic Retinopathy Study. 12 Participants with glaucoma risk factors were defined as those aged ≥65 years in conjunction with any of the suspicious signs from gonioscopy, optic disc characteristics, and visual field results. 13 Glaucoma was diagnosed according to the International Society of Geographical and Epidemiological Ophthalmology scheme. 14 AMD was graded from retinal photographs based on the Wisconsin Age-Related Maculopathy Grading System. 15 Myopic retinopathy included clinical signs of staphyloma, lacquer cracks, Fuchs spot, and myopic chorioretinal atrophy. 
Definition of Need for LVS.
Participants who needed LVS were those with BCVA < 20/40 to PL in both eyes and those in whom the cause of vision loss was untreatable. This definition excludes causes, such as refractive error, cataract, and posterior capsule opacification (PCO) after cataract extraction. The definition of LVR takes into consideration the standard VA required to drive an automobile in the United States. 16 This definition is similar to the traditional concept of “functional low vision” (FLV; note, the definition of FLV was based on the 6/18 VA cutoff point instead of 20/40) used in epidemiological surveys. 1720 Blindness was defined as those with NPL in both eyes, and participants who needed blindness care were defined as those with blindness. 
Participants who needed “any eye care service” were defined as those with the presence of need for RS, AES, CSS, or LVS. 
Attribution of Causes for AES and LVS
Given that people can have more than one cause (e.g., diabetic retinopathy and glaucoma) for AES, we did not decide which one was the principal cause. We estimated the proportion of participants who had single, dual, or multiple causes for AES. 
The principal causes for LVS were assessed by the study ophthalmologists based on clinical history, dilated eye examination, disease definition, and clinical judgment, following the same method for assigning causes for VI. The principal cause for the eye was defined as the cause estimated to be mainly responsible for vision loss. In previous surveys for “FLV” (a term equivalent to our “LVS”), when the right and left eyes had different causes of vision loss, the disorder that is “most amenable to treatment or prevention” would be considered as the principal cause. 21,22 However, it is practically difficult to distinguish which disorder is more easily treatable or preventable for people who need LVS. Beyond that, for a severely visually impaired subject with AMD in the right eye and glaucoma in the left eye, we have reasons to believe that this individual can benefit from two distinct types of vision rehabilitation services. Attributing one principal cause of LVS for this individual likely would underestimate the need of another type of LVS. Given these reasons, we decided to report the principal cause for LVS for the right and left eyes separately, not for the individual. 
Statistical Analysis
All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS Version 13.0; SPSS, Inc., Chicago, IL). Prevalence estimates and 95% confidence intervals (CIs) were calculated, either stratified by age and sex, or standardized according to the 2010 Singapore Census. Logistic regression model was used to identify factors (e.g., age, sex, hypertension) associated with the needs for CSS, RS, LVS, or AES. Age, sex, and other factors found to be significant in univariate analysis were included further in multivariate regression model. 
We projected the number of adult Asia populations who need eye care services between 2010 and 2030, using the data from the 2011 urban population report by the United Nations (UN). 23 The UN report projects the urban population across different countries between 2010 and 2030 after adjusting for mortality and live births. In the UN report, Asia is classified geographically into three regions, that is Eastern Asia (75% of the population are Chinese), South-Central Asia (66% of the population are Indians), and Southeastern and Western Asia (8% of the population are Malays). Therefore, we assumed that the epidemiologic findings from Singapore-resident Chinese, Singapore-resident Indians, and Singapore-resident Malays are representative of urban populations living in Eastern Asia, South-Central Asia, and Southeast and Western Asia, respectively. In addition, our projection was age-standardized, based on the projected age structure (i.e., the percentage of those aged 40–49, 50–59, 60–69, or 70+) of the world's population from 2010 to 2030, but we assumed that this age structure is the same across the three Asia regions. There were a number of factors that would have an impact on the estimates that we did not take into account. These included effects due to international migration, changes in the incidence/prevalence of systemic risk factors (e.g., diabetes and hypertension) over time, and changes in economic environments and improvement in primary health care over time. 
Results
A total of 3353 ethnic Chinese, 3280 ethnic Malays, and 3400 ethnic Indians had data available. Table 1 shows the demographic characteristics of the study population. Ethnic Malays appeared to be older and have lower income; ethnic Indians had a higher education level, whereas ethnic Chinese had a higher income, and lower prevalence of diabetes and hypertension than the other two ethnic groups. 
Table 1. 
 
Baseline Characteristics of the Singapore Epidemiology of Eye Disease (SEED) Participants
Table 1. 
 
Baseline Characteristics of the Singapore Epidemiology of Eye Disease (SEED) Participants
Singapore-Resident Chinese, N = 3353 (%) Singapore-Resident Malays, N = 3280 (%) Singapore-Resident Indians, N = 3400 (%)
Age group, y
 40 to 49 705 (21.0) 813 (24.8) 896 (26.4)
 50 to 59 1113 (33.2) 956 (29.2) 1097 (32.3)
 60 to 69 896 (26.7) 776 (23.7) 894 (26.3)
 70+ 639 (19.1) 729 (22.3) 513 (15.1)
Sex
 Male 1662 (49.6) 1573 (48.0) 1706 (50.2)
 Female 1691 (50.4) 1701 (52.0) 1694 (49.8)
Education
 Formal or higher 2596 (77.5) 2579 (79.0) 3077 (90.7)
 No formal education 756 (22.6) 685 (21.0) 317 (9.3)
Income per mo
  <$813 USD 1547 (47.6) 2261 (69.3) 1718 (50.6)
  ≥$813 USD 1706 (52.4) 1004 (30.8) 1680 (49.4)
Diabetes, yes 580 (17.3) 1041 (31.7) 1296 (38.1)
Hypertension, yes 1982 (59.2) 2246 (68.5) 1925 (56.7)
Table 2 shows the age-standardized proportions of individuals who needed CSS, RS, LVS, AES, and any eye care service. None of the study participants had total blindness. The proportions of persons who needed LVS generally were low, whereas the needs for CSS, RS, AES, and any eye care service were much higher. Indians had the greatest need for AES, whereas Chinese had the greatest need for RS. Overall, 76.2% of Chinese, 68.2% of Malays, and 75.5% of Indians had one or more needs for eye care services. Of people with need for eye care services, 24% of Chinese, 29% of Malays, and 31% of Indians had a dual need for eye care services, and 6% of Chinese, 5% of Malays, and 6% of Indians had a multiple need for eye care services (see Figure). 
Figure
 
Venn diagrams illustrating the overlap in proportion of participants who need RS, AES, CSS, and LVS. (A) Data for ethnic Chinese. (B) Data for ethnic Malays. (C) Data for ethnic Indians. *There were 611 Chinese (A), 766 Malays (B), and 636 Indians (C) who did not need any eye services.
Figure
 
Venn diagrams illustrating the overlap in proportion of participants who need RS, AES, CSS, and LVS. (A) Data for ethnic Chinese. (B) Data for ethnic Malays. (C) Data for ethnic Indians. *There were 611 Chinese (A), 766 Malays (B), and 636 Indians (C) who did not need any eye services.
Table 2. 
 
Prevalence of Need for Eye Care Services (%)
Table 2. 
 
Prevalence of Need for Eye Care Services (%)
Parameter RS AES CSS LVS Any Eye Care
Singapore-resident Chinese, N = 3353
 40 to 49 62.8 11.0 1.4 0.1 32.9
 50 to 59 67.3 17.7 5.1 0.5 75.7
 60 to 69 72.0 37.6 22.3 0.8 90.0
 70+ 60.4 61.4 65.1 2.2 97.0
 All 66.3 29.8 20.4 0.8 81.8
 All, age standardized (95% CI) 65.3 (62.1, 68.6) 22.4 (20.8, 24.1) 12.5 (11.5, 13.5) 0.5 (0.3, 0.9) 76.2 (72.9, 79.7)
Singapore-resident Malays, N = 3280
 40 to 49 40.2 19.5 0.7 0.3 52.3
 50 to 59 55.6 36.1 4.7 0.4 72.3
 60 to 69 64.9 52.4 22.1 1.3 89.2
 70+ 52.4 60.8 55.7 2.7 96.0
 All 53.3 41.2 19.2 1.1 76.7
 All, age standardized (95% CI) 49.6 (47.0, 52.3) 33.6 (31.6, 35.7) 11.0 (10.1, 12.0) 0.7 (0.5, 1.1) 68.2 (65.2, 71.3)
Singapore-resident Indians, N = 3400
 40 to 49 46.4 27.8 1.6 0.5 61.7
 50 to 59 61.3 40.7 6.0 0.5 80.3
 60 to 69 69.4 55.5 25.8 1.7 92.4
 70+ 61.0 68.4 65.9 2.0 98.3
 All 59.4 45.1 19.1 1.0 81.3
 All, age standardized (95% CI) 55.6 (53.0, 58.4) 40.0 (37.8, 42.2) 13.4 (12.4, 14.6) 0.8 (0.5, 1.2) 75.5 (72.4, 78.7)
Our age-standardized projection for need for eye care services for urban adults living in Asia is presented in Table 3. There was a sustained growth in the need for specific eye care services for adults aged 40+ years over time. There was a 147% overall increase, or an average annual increase of 7.4% (147%/20 years) in burden of offering eye care services from 2010 to 2030. In 2010, RS accounted for the majority of overall need (50%–65%). This was followed by AES (22%–40%), CSS (11%–13%), and LVS (0.5%–0.8%). 
Table 3. 
 
Estimated Changes in Need for Eye Care Services in Urban Adult Population in Asia between 2010 and 2030 (Thousands)
Table 3. 
 
Estimated Changes in Need for Eye Care Services in Urban Adult Population in Asia between 2010 and 2030 (Thousands)
2010 2012 2020 2025 2030
Urban adult population in Asia*
 East Asia* 286,394 330,983 392,065 438,250 480,992
 South Central Asia* 192,094 222,340 271,165 319,012 374,831
 Southeastern and Western Asia* 139,830 161,946 195,728 226,498 260,003
Estimated n of urban adults who need eye care services in East Asia
 RS 187,243 216,444 257,182 287,455 315,286
 AES 73,068 84,747 104,425 120,616 135,993
 CSS 46,046 53,506 67,332 79,958 92,275
 LVS 1,904 2,207 2,757 3,231 3,673
 Any eye care 187,111 216,432 264,705 300,688 332,625
Estimated n of urban adults who need eye care services in South Central Asia
 RS 109,622 126,947 156,803 185,372 218,212
 AES 82,147 95,227 118,932 142,197 169,040
 CSS 32,980 38,390 49,759 62,035 76,485
 LVS 1,824 2,122 2,686 3,255 3,932
 Any eye care 150,242 174,011 215,242 255,274 301,421
Estimated n of urban adults who need eye care services in Southeastern and Western Asia
 RS 71,240 82,559 101,242 117,732 135,354
 AES 51,134 59,333 74,012 87,317 101,553
 CSS 19,871 23,152 29,827 36,647 44,203
 LVS 1,231 1,433 1,813 2,193 2,615
 Any eye care 99,884 115,796 142,516 166,688 192,673
Total estimated n of urban adults who need eye care services in Asia
 RS 368,105 425,949 515,227 590,559 668,852
 AES 206,349 239,307 297,369 350,130 406,585
 CSS 98,897 115,048 146,918 178,640 212,963
 LVS 4,959 5,762 7,256 8,679 10,220
 Any eye care 437,236 506,239 622,463 722,650 826,719
In multiple regression models adjusted for various risk factors, increasing age was associated with the needs for CSS and AES, but advancing age appeared to be associated adversely with the need for RS. Low education level and lower income level were associated significantly with a greater need for CSS. Participants with diabetes were more likely to have a greater need for CSS and LVS. Male sex, higher BMI level, higher systolic blood pressure level, and lower diastolic blood pressure were associated significantly with greater need for AES (see Supplementary Material and Supplementary Table S1). 
Supplementary Table S2 (see Supplementary Material and Supplementary Table S2) demonstrates the proportion of participants who had single, dual, or multiple causes for AES stratified by ethnicity. The major single cause for LVS included DR, glaucoma, and AMD. Among the people with need for AES, 17.1% of Chinese, 15.2% of Malays, and 13.6% Indians had dual causes for AES, and 1.7% of Chinese, 0.5% of Malays, and 1.3% Indians had multiple causes for AES. 
Supplementary Table S3 (see Supplementary Material and Supplementary Table S3) shows the number and proportion of eyes that needed LVS by eye and ethnicity. The major causes for LVS included DR, AMD, glaucoma, and maculopathy, and the pattern was similar between the right and left eyes. 
In our supplementary analyses (see Supplementary Material), we also examined the age-standardized proportion of “unmet” needs for RS and CSS. The proportion of those with “unmet RS need” was 31.0% (95% CI 28.9%–33.2%), 42.5% (95% CI 40.2%–45.0%), and 28.0% (95% CI 26.2%–29.9%) for Chinese, Malays, and Indians, respectively, giving a spectacle coverage (i.e., proportion of met RS need over the combined met and unmet RS need) of 52.5%, 14.3%, and 49.3%, respectively. To facilitate comparisons, we also used a “better-seeing eye” definition of unmet RS need, that is participants who had a presenting VA of <20/40 in the better-seeing eye, but who could achieve 20/40 or better with correction in that eye. Based on the “better-seeing eye” definition, the proportion of unmet RS need was 10.7% (spectacle coverage 65.5%), 11.9% (spectacle coverage 42.7%), and 12.3% (spectacle coverage 55.7%) for Chinese, Malays, and Indians, respectively. The proportion of those with “unmet CSS need” was 5.8% (95% CI 5.2%–6.6%), 7.2% (95% CI 6.5%–8.0%), and 4.9% (95% CI 4.3%–5.7%) for Chinese, Malays, and Indians, respectively, giving a surgical coverage (i.e., proportion of met CSS need over the combined met and unmet CSS need) of 53.6%, 34.5%, and 63.4%, respectively. 
Discussion
In our population-based study of a pan-Asian multiethnic population living in a newly urbanized city (Singapore), we estimated that approximately 70% of the adult populations needed eye care services. Extrapolated to urban Asian populations, we estimated that approximately 437 million in 2010 and 827 million in 2030 may need eye care services. The needs for eye care services varied with age and ethnicity, and were substantially greater in those with diabetes and higher blood pressure. 
To our knowledge, we are the first to propose this definition scheme for need assessment and, as such, directly comparable data are not yet available in the literature. Overall, we found that the needs for RS, AES, and CSS were substantial in Singapore, although the burdens of LVS and blindness were very low. With demographic changes, the number needing eye care services in urban Asia will increase gradually in the next decades. Unlike other eye care service, AES is a lifelong care, far more difficult than providing one-time medication and operation. It is obvious that the need for AES is unmatched by the current available number of ophthalmologists in Singapore (only 2.7 per 100,000 persons). 24 This is heightened by the fact that optometrists and other eye care workers do not routinely offer AES. Aside from skilled eye care workers and efficient facilities, a sustainable primary health care system that keeps patients in-system for routine eye examination across the continuum of disease is crucial. Such a system not always is available because of low funds, poor infrastructure, and inexperience. One important finding is that one-third of the population had had a dual or multiple need for eye care (see Figure). The high prevalence of coexisting conditions challenges the prevailing “single-disease” intervention framework and supports the importance of complementary eye care strategy. 
There were ethnic variations in needs for eye care services in Singapore. Ethnic Chinese are known to be more susceptible to myopia than ethnic Malays and Indians, 25 and this probably may explain why ethnic Chinese had the greatest need for RS. In addition, genetic predisposition and lifestyle changes related to obesity, unhealthy diet, and physical inactivity may contribute to the higher prevalence of diabetes and hypertension in ethnic Malays and Indians, 26 and these ethnic differences may explain why ethnic Malays and Indians had greater needs for AES and CSS than ethnic Chinese. In our study, diabetes and hypertension are strong predictors for needs for eye care services, and it seems likely that the rising tide of these chronic diseases may lead to an increased need for eye care services if prompt action is not taken. Additionally, the needs for eye care services, particularly the need for AES, were greater among those with lower education and income levels. Although education and income traditionally have been considered as “modifiable” risk factors, the education- and income-related health disparities remain significant, and persistent in the United States and many other countries. 27 Previous health initiatives have not yielded effective and practical approaches, and, most importantly, evidence of significant outcomes in addressing these disparities. 
Another important issue concerns the “unmet” need for eye care services. It is important to note that the primary goal of our report was to measure the need (a combination of “met” and “unmet” need) for eye care services in Singapore so that we were able to project the current and future number needing eye care services in urban Asia. However, from a health system perspective, it is equally important to assess the magnitude of “unmet needs” so that prompt actions can be taken to address the gap. In our supplementary analyses (see Supplementary Material), we measured the “unmet needs” for RS and CSS, as well as spectacle coverage and cataract surgical coverage. The spectacle coverage rates (based on the “better-seeing eye” definition) in our cohort (42.7%–65.5%) were slightly lower than reported in Taiwan (71.2%), 28 but higher than reported in many developing countries (e.g., 3.4% in Nigeria, 29 3.0% in Bangladesh, 30 6.2% in Pakistan, 31 and 17.4% in India 32 ). Likewise, our cataract surgical coverage rates (34.5%–63.4%) were slightly lower than reported in Latinos in the United States (65.7%), 33 but generally higher than reported in developing regions (well below 50%). 3437 Unfortunately, our study did not collect detailed information on the “unmet needs” for AES and LVS. Despite the lack of information in our report, the uptake of annual eye examination is known to be very low across the world, even among high risk populations living in developed countries. In the United States, for example, less than 50% of people with diabetes had undergone annual eye examination, 38 and the figure was even lower among socially disadvantaged populations, such as ethnic minorities, the uninsured, and those living in rural areas. 39 Studies in Asia also showed a low proportion of diabetes subjects receiving recommended annual eye examination (33.3% in China and 15.3% in Indonesia). 40,41 Unlike AES, fewer data are available on the unmet need of LVS. A global questionnaire survey showed that approximately half of the African and Western Pacific regions countries did not provide LVS, and very few countries had more than 10 vision rehabilitation professionals per 10 million of population. 42  
Our reconsideration and classification of the need for specific eye care services are prompted by the difficulties in identifying and classifying individuals who need eye care. This framework is not definitive, and is intended as an operational approach for epidemiologic survey only. For example, our AES definition may not be valid in “real world” clinical settings, where the interval of periodic eye examination should depend on the patients' specific conditions and severity, and could be subject to the clinician's discretionary judgment. Additionally, our use of 20/40 as the cut-off point for identifying CSS, RS, and LVS is arbitrary and should not be used for rationing patients. An individualized visual functioning assessment in conjunction with a comprehensive eye examination may provide a better assessment of patients' visual performance and specific needs. 43 Ironically, many health authorities and governments agencies have used the 6/18 VA cut-off point (usually in conjunction with a visual field threshold value) to decide who would be eligible for free vision rehabilitation services and who would not. 44,45 Another concern is that we defined the need for LVS based on presence of “untreatable eye disease,” which is problematic as the concept of “untreatable eye disease” evolves with time. For example, the wide use of anti-angiogenic agents (e.g., bevacizumab and ranibizumab) in urban settings has now transformed many cases of AMD and retinal vein occlusion into treatable lesions, although this treatment is not widely available in the least developed countries. 
The strengths of our study include a large and representative sample size, the use of standardized protocols that allow valid classification of eye diseases, and the use of reliable age- and ethnicity-specific data for projection. Our study is limited by the fact that we did not obtain detailed information regarding the awareness, supply (i.e., what is provided), demand (i.e., what individuals ask for), and use of eye care services. These factors may have influenced the needs for eye care services in unmeasured ways. Furthermore, we did not collect detailed visual field data for every participant, and thus we only used VA level to identify individuals who needed eye care. A visual field threshold should be included in future epidemiologic surveys when it is available. In addition, the low response rate (72.8%–78.7%) among the three ethnic groups may be a potential source of bias. Finally, our study population may not be fully representative of the other urban Asia populations, because of the differences in prevalence of major eye diseases, and health care systems across different countries. Specifically, we made the crude assumption that the data from Singapore-resident Malays can be generalized to Southeast and Western Asia. This extrapolation may not be entirely accurate, since Malays only account for 8% of populations in the region. 22  
In summary, our study showed that, with the exception of LVS, the need for CSS, RS, and AES in Singapore is substantial. We project that the future demand for eye care service in Asia is significant and increasing, and hence there is a need to expand the provision of primary eye care services and improve the capacity for eye care professionals other than ophthalmologists. Our report also calls for long-term solutions to reduce the prevalence of diabetes and hypertension. As the number with diabetes and hypertension continues to grow in Asia, so does the demand for eye care services. 
Supplementary Materials
References
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Footnotes
 Supported by Biomedical Research Council (BMRC) Grant 08/1/35/19/550 and National Medical Research Council (NMRC) Grant STaR/0003/2008, Singapore. The authors alone are responsible for the content and writing of the paper.
Footnotes
 Presented at the annual meeting of the Association for Research in Vision and Ophthalmology, Fort Lauderdale, Florida, May 6–10, 2012.
Footnotes
 Disclosure: Y. Zheng, None; C.-Y. Cheng, None; E.L. Lamoureux, None; P.P.C. Chiang, None; A. Rahman Anuar, None; J.J. Wang, None; P. Mitchell, None; S.-M. Saw, None; T.Y. Wong, None
Figure
 
Venn diagrams illustrating the overlap in proportion of participants who need RS, AES, CSS, and LVS. (A) Data for ethnic Chinese. (B) Data for ethnic Malays. (C) Data for ethnic Indians. *There were 611 Chinese (A), 766 Malays (B), and 636 Indians (C) who did not need any eye services.
Figure
 
Venn diagrams illustrating the overlap in proportion of participants who need RS, AES, CSS, and LVS. (A) Data for ethnic Chinese. (B) Data for ethnic Malays. (C) Data for ethnic Indians. *There were 611 Chinese (A), 766 Malays (B), and 636 Indians (C) who did not need any eye services.
Table 1. 
 
Baseline Characteristics of the Singapore Epidemiology of Eye Disease (SEED) Participants
Table 1. 
 
Baseline Characteristics of the Singapore Epidemiology of Eye Disease (SEED) Participants
Singapore-Resident Chinese, N = 3353 (%) Singapore-Resident Malays, N = 3280 (%) Singapore-Resident Indians, N = 3400 (%)
Age group, y
 40 to 49 705 (21.0) 813 (24.8) 896 (26.4)
 50 to 59 1113 (33.2) 956 (29.2) 1097 (32.3)
 60 to 69 896 (26.7) 776 (23.7) 894 (26.3)
 70+ 639 (19.1) 729 (22.3) 513 (15.1)
Sex
 Male 1662 (49.6) 1573 (48.0) 1706 (50.2)
 Female 1691 (50.4) 1701 (52.0) 1694 (49.8)
Education
 Formal or higher 2596 (77.5) 2579 (79.0) 3077 (90.7)
 No formal education 756 (22.6) 685 (21.0) 317 (9.3)
Income per mo
  <$813 USD 1547 (47.6) 2261 (69.3) 1718 (50.6)
  ≥$813 USD 1706 (52.4) 1004 (30.8) 1680 (49.4)
Diabetes, yes 580 (17.3) 1041 (31.7) 1296 (38.1)
Hypertension, yes 1982 (59.2) 2246 (68.5) 1925 (56.7)
Table 2. 
 
Prevalence of Need for Eye Care Services (%)
Table 2. 
 
Prevalence of Need for Eye Care Services (%)
Parameter RS AES CSS LVS Any Eye Care
Singapore-resident Chinese, N = 3353
 40 to 49 62.8 11.0 1.4 0.1 32.9
 50 to 59 67.3 17.7 5.1 0.5 75.7
 60 to 69 72.0 37.6 22.3 0.8 90.0
 70+ 60.4 61.4 65.1 2.2 97.0
 All 66.3 29.8 20.4 0.8 81.8
 All, age standardized (95% CI) 65.3 (62.1, 68.6) 22.4 (20.8, 24.1) 12.5 (11.5, 13.5) 0.5 (0.3, 0.9) 76.2 (72.9, 79.7)
Singapore-resident Malays, N = 3280
 40 to 49 40.2 19.5 0.7 0.3 52.3
 50 to 59 55.6 36.1 4.7 0.4 72.3
 60 to 69 64.9 52.4 22.1 1.3 89.2
 70+ 52.4 60.8 55.7 2.7 96.0
 All 53.3 41.2 19.2 1.1 76.7
 All, age standardized (95% CI) 49.6 (47.0, 52.3) 33.6 (31.6, 35.7) 11.0 (10.1, 12.0) 0.7 (0.5, 1.1) 68.2 (65.2, 71.3)
Singapore-resident Indians, N = 3400
 40 to 49 46.4 27.8 1.6 0.5 61.7
 50 to 59 61.3 40.7 6.0 0.5 80.3
 60 to 69 69.4 55.5 25.8 1.7 92.4
 70+ 61.0 68.4 65.9 2.0 98.3
 All 59.4 45.1 19.1 1.0 81.3
 All, age standardized (95% CI) 55.6 (53.0, 58.4) 40.0 (37.8, 42.2) 13.4 (12.4, 14.6) 0.8 (0.5, 1.2) 75.5 (72.4, 78.7)
Table 3. 
 
Estimated Changes in Need for Eye Care Services in Urban Adult Population in Asia between 2010 and 2030 (Thousands)
Table 3. 
 
Estimated Changes in Need for Eye Care Services in Urban Adult Population in Asia between 2010 and 2030 (Thousands)
2010 2012 2020 2025 2030
Urban adult population in Asia*
 East Asia* 286,394 330,983 392,065 438,250 480,992
 South Central Asia* 192,094 222,340 271,165 319,012 374,831
 Southeastern and Western Asia* 139,830 161,946 195,728 226,498 260,003
Estimated n of urban adults who need eye care services in East Asia
 RS 187,243 216,444 257,182 287,455 315,286
 AES 73,068 84,747 104,425 120,616 135,993
 CSS 46,046 53,506 67,332 79,958 92,275
 LVS 1,904 2,207 2,757 3,231 3,673
 Any eye care 187,111 216,432 264,705 300,688 332,625
Estimated n of urban adults who need eye care services in South Central Asia
 RS 109,622 126,947 156,803 185,372 218,212
 AES 82,147 95,227 118,932 142,197 169,040
 CSS 32,980 38,390 49,759 62,035 76,485
 LVS 1,824 2,122 2,686 3,255 3,932
 Any eye care 150,242 174,011 215,242 255,274 301,421
Estimated n of urban adults who need eye care services in Southeastern and Western Asia
 RS 71,240 82,559 101,242 117,732 135,354
 AES 51,134 59,333 74,012 87,317 101,553
 CSS 19,871 23,152 29,827 36,647 44,203
 LVS 1,231 1,433 1,813 2,193 2,615
 Any eye care 99,884 115,796 142,516 166,688 192,673
Total estimated n of urban adults who need eye care services in Asia
 RS 368,105 425,949 515,227 590,559 668,852
 AES 206,349 239,307 297,369 350,130 406,585
 CSS 98,897 115,048 146,918 178,640 212,963
 LVS 4,959 5,762 7,256 8,679 10,220
 Any eye care 437,236 506,239 622,463 722,650 826,719
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