August 2000
Volume 41, Issue 9
Free
Clinical and Epidemiologic Research  |   August 2000
Prevalence and Risk Factors for Refractive Errors in Adult Chinese in Singapore
Author Affiliations
  • Tien Yin Wong
    From the Singapore National Eye Centre, Singapore; the
    Department of Ophthalmology and the
    Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison; the
  • Paul J. Foster
    From the Singapore National Eye Centre, Singapore; the
    Institute of Ophthalmology, University College London, United Kingdom; and the
  • Joscelin Hee
    From the Singapore National Eye Centre, Singapore; the
  • Tze Pin Ng
    Department of Community, Occupational and Family Medicine, National University of Singapore; the
  • James M. Tielsch
    Department of International Health, Johns Hopkins University School of Public Health, Baltimore, Maryland.
  • Sek Jin Chew
    From the Singapore National Eye Centre, Singapore; the
    Department of Ophthalmology and the
  • Gordon J. Johnson
    Institute of Ophthalmology, University College London, United Kingdom; and the
  • Steve K. L. Seah
    From the Singapore National Eye Centre, Singapore; the
Investigative Ophthalmology & Visual Science August 2000, Vol.41, 2486-2494. doi:
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      Tien Yin Wong, Paul J. Foster, Joscelin Hee, Tze Pin Ng, James M. Tielsch, Sek Jin Chew, Gordon J. Johnson, Steve K. L. Seah; Prevalence and Risk Factors for Refractive Errors in Adult Chinese in Singapore. Invest. Ophthalmol. Vis. Sci. 2000;41(9):2486-2494.

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

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Abstract

purpose. To determine the epidemiology of refractive errors in an adult Chinese population in Singapore.

methods. A disproportionate, stratified, clustered, random-sampling procedure was used to select names of 2000 Chinese people aged 40 to 79 years from the 1996 Singapore electoral register in the Tanjong Pagar district in Singapore. These people were invited to a centralized clinic for a comprehensive eye examination, including refraction. Refraction was also performed on nonrespondents in their homes. Myopia, high myopia, and hyperopia were defined as a spherical equivalent (SE) in the right eye of less than −0.5 D, less than −5.0 D, and more than+ 0.5 D, respectively. Astigmatism was defined as less than −0.5 D of cylinder. Anisometropia was defined as a difference in SE of more than 1.0 D between the two eyes. Only phakic eyes were analyzed.

results. From 1717 eligible people, 1232 (71.8%) were examined. Adjusted to the 1997 Singapore population, the overall prevalence of myopia, hyperopia, astigmatism, and anisometropia was 38.7% (95% confidence interval[ CI]: 35.5, 42.1), 28.4% (95% CI: 25.3, 31.3), 37.8% (95% CI: 34.6, 41.1), and 15.9% (95% CI: 13.5, 18.4), respectively. The prevalence of high myopia was 9.1% (95% CI: 7.2, 11.2), with women having significantly higher rates than men. The age pattern of myopia was bimodal, with higher prevalence in the 40 to 49 and 70 to 81 age groups and lower prevalence between those age ranges. Prevalence was reversed in hyperopia, with a higher prevalence in subjects aged 50 to 69. There was a monotonic increase in prevalence with age for both astigmatism and anisometropia. Increasing educational levels, higher individual income, professional or office-related occupations, better housing, and greater severity of nuclear opacity were all significantly associated with higher rates of myopia, after adjustment for age and sex.

conclusions. The results indicate that whereas myopia is 1.5 to 2.5 times more prevalent in adult Chinese residing in Singapore than in similarly aged European-derived populations in the United States and Australia, the sociodemographic associations are similar.

The few available population-based studies on myopia and other refractive errors have been conducted almost solely in white European-derived populations. In the 1970s, a prevalence of 25% was reported in a United States study among persons aged 12 to 54 years. 1 In persons more than 40 years of age, prevalence observed in recent surveys in the United States was 22.7% in the Baltimore Eye Survey 2 and 26.2% in the Beaver Dam Study. 3 In Australia, the overall prevalence of myopia was 17% in the Visual Impairment Project 4 and 15% in the Blue Mountains Eye Study, 5 and in Israel, a prevalence of 18.4% was reported. 6  
For other racial groups, population-based data are sparse. In the Baltimore Eye Survey, the prevalence of myopia in blacks (19.4%) was lower than in whites (28.1%). 2 In the Barbados Eye Study the prevalence of myopia in black persons more than 40 years of age was 21.9%. 7  
In East Asia, although the prevalence of myopia is often presumed to be much higher, precise population-based data are not available. 8 At present, the available information is based on studies conducted in selected subgroups of the population. In Taiwan, two studies covering school children aged 6 to 18 showed a prevalence of more than 80% by age 18 years. 9 10 Another study in a Japanese student population showed an overall prevalence of approximately 50%, 11 and a pilot study in Hong Kong in 355 adult Chinese aged 40 or more years showed a prevalence of approximately 40%. 12 In Singapore, several studies in students and army recruits have indicated that the prevalence may be among the highest in the world. 13 14 However, the prevalence of myopia in the adult population of Singapore or other East Asian countries is not known. 
For other refractive errors such as hyperopia, astigmatism, and anisometropia, the prevalences have been estimated in the adult white and black populations, 1 2 3 4 5 6 7 but information in adult East Asian populations is limited. 
Although the cause of myopia is debatable, 15 16 risk factors in the European-derived populations are well documented. Non–cataract-related myopia rates have been reported to be associated with higher education, 1 2 3 4 5 17 certain occupations associated with near work 4 7 and higher family income. 1 Whether the same risk factors for myopia apply in East Asian countries is less clear. 
The purpose of this study was to estimate the prevalence of different refractive errors in an adult Chinese population aged 40 years and more in Singapore. In particular, we were interested in evaluating risk factors associated with myopia in Chinese. Singapore is an urban city-state with a population of 3.2 million, 78% of whom are ethnic Chinese. Because a large number of Chinese residents in our study age group were first-generation immigrants from the southern provinces of Fujian and Guandong in China, some generalizability of our data to the Chinese population is possible. 
Methods
The study was part of a population-based survey of ocular disorders among adult Chinese living in Singapore. The 1996 Singapore electoral register was used as the sampling frame in this study. Because electoral registration is a legal requirement in Singapore, the register provides a complete record of all Singapore citizens aged 21 years and older. Tanjong Pagar is located in the center of Singapore and was chosen because the population demographics of the Chinese residents are representative of the remainder of Singapore. The electoral register listed names of 15,082 Chinese people aged between 40 and 79 years and residing in the district. Two thousand (13.3%) names were selected by a disproportionate (with more weights given to the older age groups), stratified, clustered, random-sampling method. These persons were invited for a comprehensive eye examination at the study center. After this, domiciliary examinations of nonresponding persons were performed by a field team. The study was performed between October 10, 1997, and August 14, 1998. 
Procedures
Before each examination, identity was verified from subjects’ national identity cards, after which written, informed consent was obtained after an explanation of the study in Chinese, one of the Chinese dialects, or English. Consent was signed in Chinese in 46% of the participants, in English in 44%, and a cross in the remaining 10%. 
Visual acuity was assessed in the following sequence as part of a standardized clinical examination. Habitual visual acuity was first determined with the initial distance spectacle correction (if any) using the logMAR chart (The Lighthouse, Long Island City, NY) under standard lighting conditions at 4 m. 18 The visual acuity testing was performed as follows: Subjects began reading at the 6/12 equivalent line (0.3). If they were able to read more than three letters on that line, they proceeded to the next line below, until two mistakes were made on one line (i.e., only three letters correctly identified on that line). This line would then be recorded as the habitual visual acuity. If they were unable to read at least three letters, they would begin to read the line above and continued this process until at least three letters on one line had been read. If unable to read the chart at 4 m, the subject was moved to 2 m and then to 1 m from the chart. If subjects were unable to achieve minimum recordable logMAR acuity, the vision was recorded as perception or nonperception of light, as appropriate. 
Refraction data on all subjects were recorded as follows. An initial objective refraction result was recorded by using an autorefractor (Retinomax K-plus; Nikon, Tokyo, Japan). Manual subjective refraction was then attempted to refine vision, using the results of the objective refraction as the starting point. The best corrected visual acuity was found, and both the derived refraction data and the visual acuity were recorded. Because of the age of our study population, no cycloplegia was used. 
To maximize response rates, those who did not attend the clinic visit were offered an abbreviated examination in their homes. For this domiciliary examination, habitual visual acuity was assessed using a 3-m Snellen chart, with distance spectacle correction if needed. If the visual acuity was less than 6/12, the acuity was remeasured using a pinhole (best corrected visual acuity). Refraction was assessed using a handheld autorefractor (Retinomax K-plus; Nikon, Toyko, Japan). No manual subjective refraction was conducted on these subjects. 
Definitions and Analysis
For this study, refraction data were based on subjective refraction when participants had both subjective and objective refraction and on objective refraction when only this information was available. Preliminary analysis of data from participants with phakic eyes who had both types of refraction in the right eye (n = 981) indicated that the overall correlation between objective and subjective refraction in spherical equivalents (SEs) was high (ρ = 0.98, P < 0.001). Other reports will examine in detail the variations in correlation between the two methods of refraction among different age groups and refractive status. For our definitions of emmetropia, myopia, hyperopia, and anisometropia, the refractive data were converted to SE, which is derived by adding the spherical component of the refraction to half the cylindrical component. The data on the right and left eyes were initially analyzed separately. However, because the correlation between the right and left eyes for SE was high (ρ = 0.83, P < 0.001), for the analysis of all refractive errors other than anisometropia, we present data on only the right eye. Emmetropia was defined as an SE of between −0.5 and 0.5 D. Myopia was defined and analyzed on two levels separately: an SE of less than −0.5 D and less than −1.0 D. High myopia was defined as SE of less than −5.0 D. Hyperopia was defined an SE of more than +0.5D, whereas anisometropia was defined as an SE difference between the right and left eyes of more than 1.0 D. Astigmatism was analyzed in minus cylinders and was defined as a less than −0.5 D of cylinder, without reference to the axis. These definitions were chosen to enable direct comparison between our data and those in other studies. 1 2 3 4 5  
Lens nuclear opacity was graded by slit lamp examination using the modified Lens Opacity Classification System (LOCS) III score. 19 Under this scoring system, nuclear opacity was graded in increasing severity from grade 1 to grade 6. 
Because our study population was selected based on a disproportionate sampling technique (with more weights given to the older age groups), to provide a more accurate estimate of the actual prevalence of refractive errors in the population, age-adjusted rates were calculated based on the appropriate 1997 Singapore Chinese population (men, women, and both men and women). 20 The associations between gender, age, and other socioeconomic variables, as well as lens nuclear opacity and the risk of myopia and high myopia were estimated by the odds ratio (OR) and its 95% confidence interval (CI). Multiple logistic regression was used to assess the mutually confounding effect of these variables on the risk of myopia and high myopia and to obtain adjusted estimates of the individual OR. Statistical analyses of the data were performed by a computer program (SPSS, Chicago, IL). 
This study was approved by the ethics committee of Singapore National Eye Center and performed in accordance with the tenets of the World Medical Association’s Declaration of Helsinki. 
Results
Among the 2000 subjects selected, 46 died and 235 moved to addresses outside Tanjong Pagar district before or during the study period. Two persons were considered ineligible for the survey (one being near death and the other severely mentally disabled). At the initial research clinic, 1072 were examined. An additional 160 subjects were examined in their homes. Of these, 18 were then referred to the research clinic for definite diagnostic examination. The total number of subjects examined in either setting was 1232. Therefore, the overall response rate was 71.8% (1232 of 1717 subjects), whereas the response rate based only on the clinic examination was 63.5% (1090 of 1717 subjects). 
Of the 1232 subjects examined, 103 (8.4%) had had cataract extraction in their right eyes and were excluded. Sixteen (1.3%) had no refraction data for their right eyes, including four subjects with corneal opacities, dense cataracts, and other media opacities in which accurate refraction could not be performed. 
Further analyses on myopia, hyperopia, and astigmatism were based on refraction data from the 1113 subjects with phakic eyes with refraction in the right eye. Table 1 shows the characteristics of subjects included in and excluded from the analysis. In general, subjects included in the analysis were younger; more likely to be professionals, office workers, and salespeople; lived in better housing; and had higher education levels and individual income. There was little difference between the two groups in gender and smoking status. 
Of the 1113 subjects, 500 (44.9%) were men, and 613 (55.1%) were women. The mean age of these subjects was 58.8 ± 11.0 (SD) years. There was no significant difference in mean ages between men (59.2 ± 11.0 years) and women (58.5 ± 11.0 years; t-test, P = 0.28). 
Figure 1 shows the distribution of the refraction in SEs in the study population. A total of 324 (29.1%) subjects were classified as emmetropic, 389 (35.0%) were classified as myopic (worse than −0.5 D), and 400 (35.9%) were hyperopic. Seventy-seven subjects (6.9%) had high myopia. This formed nearly 20% of the myopes in the study population. In addition, astigmatism was present in 489 subjects (43.9%). 
The crude and age-adjusted prevalence of emmetropia and different refractive errors are shown in Table 2 . The overall age-adjusted prevalence of myopia (worse than −0.5 D) was 38.7% (95% CI: 35.5, 42.1), with higher rates in women (40.5%, 95% CI: 35.3, 44.5) than in men (36.5%, 95% CI: 31.8, 41.0). There was no statistical difference between the two sexes in age-adjusted rates of all refractive errors, except for high myopia, in which women had significantly higher prevalence (χ2 test, P = 0.04). 
For the analysis of anisometropia, subjects who had had cataract surgery in either eyes were excluded (n = 131). Also excluded were subjects without refractive data in either eye (n= 25). Of the remaining 1076 subjects with phakic eyes with refractive data in both eyes, 215 (20.0%) had anisometropia (SE difference between the right and left eyes >1.0 D). The age-adjusted prevalence of anisometropia is shown in Table 2
There were distinctive age and sex patterns for different refractive errors (Table 3) . For example, for myopia (Fig. 2) , the highest prevalence was in the 40 to 49 age group, and the second highest was in the 70 to 81 age group. Lower prevalence was seen between these two age groups. The highest prevalence in our population occurred in women aged 40 to 49 (51.7%, 95% CI: 43.7, 59.6) and the lowest in men aged 50 to 59 (25.2%, 95% CI: 17.3, 33.2). In contrast, the age pattern was reversed for hyperopia, with highest prevalence in the 60 to 69 age group (Fig. 2) . For both astigmatism and anisometropia, there was a monotonic increase in prevalence with age in both sexes (Fig. 3)
We further examined the prevalence of different refractive errors in subgroups of the population (Table 4) . Increasing levels of education, better housing, and higher individual monthly income were significantly associated with increasing prevalence of myopia and high myopia. Professionals and office workers had the highest prevalence of myopia (52.4%) in comparison with other occupations, whereas laborers had the lowest prevalence (25.9%). Subjects with nuclear cataract who had LOCS III scores of 5 or 6 had the highest levels of myopia, followed by subjects with LOCS III scores of 1 or 2. The lowest rates of myopia were seen in subjects with moderate nuclear cataract (LOCS scores of 3 or 4). This pattern was probably related to the confounding effects of age on the prevalence of nuclear cataract and myopia, which was explored further with multivariate analysis (see Table 5 and the Discussion section). Smokers had a lower prevalence of myopia and high myopia, but the relationship was again likely to be confounded by age. 
The risk of different associations with myopia and high myopia were analyzed in various multivariate models and are selectively presented in Table 5 . When adjusted for age, there was no difference in risk of myopia between men and women. However, women had a 69% greater risk of high myopia (age-adjusted odds ratio [OR], 1.69, 95% CI: 1.03, 2.77). The lowest risk of myopia was seen in both genders aged 50 to 59 years. Men and women aged 40 to 49 had an approximately one and a half times higher risk of myopia than those aged 50 to 59. The age pattern was exaggerated for high myopia in both genders. 
Increasing education, better housing, and higher individual income were associated with higher odds of myopia and high myopia, after adjusting for age and sex. Professionals and office workers had higher odds of myopia compared with those in other occupations, after adjusting for age and sex. Finally, nuclear opacity was associated independently with myopia and high myopia, after adjusting for age, sex, and individual income (as an indicator for socioeconomic status). Similar results for the association with nuclear opacity were obtained when adjustment for socioeconomic status was made with other proxy variables, such as housing types and education, evidenced by the high correlation of these variables with one another. 
Discussion
To our knowledge, this study is the first to provide population-based data on the prevalence of refractive errors in adult East Asians. We observed an overall prevalence of myopia of 38.7% in our Chinese residents, which is between one and a half to two and a half times the rate seen in similarly aged populations in whites 2 3 4 5 and blacks. 2 7 This confirms a widely held view that myopia is more common in East Asia, based on data in previous studies in selected populations. 8 9 10 11 12 13 14 In addition, our data show that the same sociodemographic (higher education, higher income, better housing, and occupations associated with near work) and ocular (increasing lens opacity) risk factors for myopia exist between Chinese in Singapore and the European-derived populations. 
There are difficulties in direct comparison of rates of myopia with data in other studies, because of differing ages of participants, definitions of myopia, inclusion criteria, and research methodology. In the Beaver Dam study (age range: 43–84 years), an overall prevalence of myopia of 26.2% was found in persons with phakic eyes who had better than 20/40 visual acuity in at least one eye. 3 In the Visual Impairment Project in Victoria, Australia, a prevalence of 17% was observed in the population (40–98 years), after exclusion of participants with aphakia or pseudophakia, corneal diseases, and media opacities associated with worse than 20/60 visual acuities. 4 In the Blue Mountains Eye Study in Australia (age range: 49–97 years), the 15% myopia prevalence reported could not be directly compared with that in the current study, because their study population was a decade older. 5 Similarly, the National Health and Nutrition Examination Survey (NHANES) in 1971 estimated that 25% of the population was myopic, but the subjects were much younger than ours (12–54 years). 1 In addition, the investigators in that study defined myopia as any negative SE, based on refraction in participants whose visual acuity was worse than 20/40 and lensometry in those whose visual acuity was 20/40 or better. In the Baltimore Eye Survey (age range: 40–89 years), a prevalence of 22.7% was noted in white and black subjects aged 40 years and more. 2 In that study as well as in ours, participants were older than 40 years, myopia was defined as SE of worse than −0.5 D, and all had noncycloplegic refraction, regardless of their visual acuity or whether they wore spectacles. 
The racial and ethnic variation of myopia has been reported in population-based studies in European-derived societies. For other populations, limited data are available. Racial variation was shown in the United States, where the NHANES report indicated that the prevalence of myopia was significantly lower among blacks than whites. 1 Using the same definition of myopia as in the Beaver Dam study and after adjustments for age, gender, and education, the Baltimore Eye Survey reported a 28.1% prevalence in whites (similar to the Beaver Dam prevalence of 26.2%) but only 19.4% in blacks. 2 The prevalence of myopia in the black population in Barbados (age range: 40–84 years) was recently shown to be 21.9%. 7 In contrast, the prevalence of myopia has been reported to be lower than 5% in Australian Aborigines 21 and in the populations in the Solomon Islands 22 and Malawi. 23  
In East Asia, the apparent high prevalence of myopia was first observed in the 1930s in China. 24 Since then, several studies have confirmed that the prevalence may be above 50% in selected high-risk populations. 9 10 11 13 14 Wensor et al. 4 noted that residents in Australia who had been born in Southeast Asia had a higher prevalence of myopia than those born elsewhere, even after controlling for education. Our study adds support to the suggestion that the prevalence of myopia in East Asians is higher. There are no data that adequately explain the high prevalence of myopia in East Asians. Both environmental and genetic factors appear to play important roles. 8 15 16 Possible environmental reasons suggested include an apparent increase in formal education and more time spent on near work tasks by East Asians. 8 Genetic variations between East Asians and European-derived populations have also been suggested but not substantiated. 8 15 16  
One particular concern is that almost 7% of our population could be classified as having high myopia (worse than −5.0 D). Adjusted to the adult Chinese population aged 40 to 79 years in Singapore, the prevalence of high myopia was nearly 10%. This figure is higher than data in reports from European-derived populations. In the Visual Impairment Project, high myopia of similar definition was found in less than 2% of their subjects with myopia. 4 The prevalence of high myopes in the Baltimore Eye Survey, in which a slightly different definition was used for high myopia (worse than −6.0 D), was approximately 1.4%. 2 There are two important ophthalmic implications in the rate of high myopia. First, high myopia has a higher risk of cataract, glaucoma, myopic macular degeneration, and retinal detachment. 15 Second, the results of refractive surgery are less predictable in subjects with high myopia. 25  
Other demographic patterns have been noted in European-derived populations with refractive errors. Age has been highly correlated with the prevalence of different refractive errors. For both astigmatism and anisometropia, there was an age-dependent increase in prevalence in our study that was similar to that reported in white populations. 2 5 For myopia, both population and non–population-based studies have shown that the prevalence generally follows a bimodal pattern in adults, initially declining with age and then increasing in the upper age groups. 2 3 4 Because the age pattern of myopia was described half a century ago, 26 the exact rationale for this observation is still controversial. One theory involves changes in the refractive index gradient of the lens with age. 27 In the Beaver Dam Study, increasing level of nuclear opacity was an important determinant of the age-related increase in myopia after 70 years. 28 An alternative explanation to age-related variations is that a real increase in the prevalence of myopia has occurred between the younger population compared with older people. 29 It seems likely that both mechanisms are operating in our population as well. 
The association of gender with refractive errors has not been well established. In the NHANES report, the prevalence of myopia was significantly lower in men than women. 1 In the Beaver Dam study, a small gender difference was seen in the rates of myopia 3 but in the Baltimore Eye Survey, no gender difference was found. 2 Similarly, our study does not indicate significant gender differences. Although women were more likely to have high myopia (Table 5) , the overall rates of myopia and other refractive errors were similar in both genders across the entire age range (Table 3)
Educational status, occupation, and income have been among the most frequently noted socioeconomic associations of myopia and hyperopia. These associations may be an indicator of near work and support the use–abuse theory for myopia. 15 16 In the NHANES study, the prevalence of myopia increased with family income and educational level. 1 Both the Baltimore and Beaver Dam studies showed a monotonic relationship between education and myopia. 2 3 Our study found a direct relationship between increasing education and myopia and an inverse relationship with hyperopia. The Visual Impairment Project in Melbourne found that professionals and clerks had higher risks of myopia. 4 One possible explanation was the association of these occupations with greater amounts of near work. We found similar higher odds of myopia in people who were professionals and office workers. Income and better housing are indicators of socioeconomic status and have been reported to be related to myopia in white populations, 1 as was similarly seen in ours. As expected, we observed no distinctive trends of sociodemographic factors with either astigmatism or anisometropia. 
Lens opacity appears to be an important ocular determinant of refractive error. There was a dose–response pattern between level of lens opacity and rate of astigmatism. For myopia, persons with the highest levels of nuclear opacity in our study (LOCS III grade 5 or 6) had an OR of 16 compared with the lowest levels (LOCS III grade 1 or 2). This was apparent also in the Visual Impairment Project in Australia. 4  
In conclusion, our study provides further epidemiologic data on the prevalence of refractive errors in an adult Chinese population in Asia. First, we showed that the prevalence of myopia was one and a half to two and a half times higher than in similarly aged European derived populations in the United States and Australia. Second, up to 10% of our population had high myopia, with potentially serious ophthalmic implications. Third, although the rate of myopia was different from that in whites and blacks, the sociodemographic and ocular risk factors were similar, indicating a common pathophysiological basis for myopia. 
Table 1.
 
Comparison of Subjects Included in and Excluded from Refraction Data Analyses
Table 1.
 
Comparison of Subjects Included in and Excluded from Refraction Data Analyses
Included (n = 1113)Excluded (n = 119)P*
Age
40–49275 (24.7)1 (0.8)<0.001
50–59303 (27.2)3 (2.5)
60–69307 (27.6)36 (30.3)
70–81228 (20.5)79 (66.4)
Sex
Females613 (55.1)62 (52.1)0.05
Education
None277 (25.2)47 (41.2)<0.001
Primary446 (40.3)54 (47.4)
Secondary300 (27.2)10 (8.8)
Tertiary80 (7.3)3 (2.6)
Unknown10 (—)5 (—)
Occupation
Professionals and office workers210 (19.0)14 (12.2)<0.001
Salespersons183 (16.5)11 (9.6)
Production operators231 (20.9)27 (23.5)
Laborers and cleaners189 (17.1)22 (19.1)
Homemakers33 (23.5)32 (27.8)
Unemployed260 (3.0)9 (7.8)
Unknown7 (—)4 (—)
Housing
1–2 room flats204 (18.5)31 (27.0)0.09
3 room flats594 (53.9)64 (55.7)
4–5 room flats280 (25.4)19 (16.5)
Executive flats18 (1.6)1 (0.9)
Private housing7 (0.6)0 (0)
Unknown10 (—)4 (—)
Individual monthly income
Less than $1000688 (62.9)91 (79.8)<0.001
$1000–2000190 (17.4)3 (2.6)
$2000–300065 (5.9)0 (0)
More than $300051 (4.7)0 (0)
Retired100 (9.1)20 (17.5)
Unknown19 (—)5 (—)
Smoking
Yes199 (18.0)20 (17.4)0.87
No906 (82.0)95 (82.6)
Unknown8 (—)4 (—)
Figure 1.
 
Frequency distribution of SEs in the right eye in Chinese residents in Singapore.
Figure 1.
 
Frequency distribution of SEs in the right eye in Chinese residents in Singapore.
Table 2.
 
Crude and Age-Adjusted Prevalence of Refractive Errors in Chinese Residents in Singapore
Table 2.
 
Crude and Age-Adjusted Prevalence of Refractive Errors in Chinese Residents in Singapore
MalesFemalesAll
nCr %Adj %*(95% CI)nCr %Adj %, †(95% CI)nCr %Adj %, ‡(95% CI)
Emmetropia16533.036.7(32.0, 41.2)15925.929.7(25.4, 34.0)32429.132.9(29.7, 36.1)
Myopia (<−0.5 D SE)16533.036.7(32.0, 41.2)22436.540.5(35.3, 44.5)38935.038.7(35.5, 42.1)
Myopia (<−1.0 D SE)13126.229.0(24.6, 33.3)18129.534.0(29.4, 38.3)31228.031.9(28.7, 35.0)
High myopia (<−5.0 D SE)265.27.5(5.1, 10.4)518.310.5(7.6, 13.3)776.99.1(7.2, 11.2)
Hyperopia (>+0.5 D SE)17034.026.8(22.5, 31.0)23037.529.8(25.4, 34.0)40035.928.4(25.3, 31.3)
Astigmatism (<−0.5 D C)21142.234.1(29.4, 38.5)27845.440.9(36.2, 45.5)48943.937.8(34.6, 41.1)
Anisometropia (>1.0 D SE diff)10121.115.6(12.1, 19.0)11419.116.9(13.4, 20.6)21520.015.9(13.5, 18.4)
Table 3.
 
Prevalence of Refractive Errors in Chinese Residents in Singapore by Age and Sex
Table 3.
 
Prevalence of Refractive Errors in Chinese Residents in Singapore by Age and Sex
SexAge (y)High Myopia (< −5.0 D SE)Myopia (< −0.5 D SE)Hyperopia (>0.5 D SE)Astigmatism (< −0.5 D C)Anisometropia (>1.0 D SE diff)
n%(95% CI)n%(95% CI)n%(95% CI)n%(95% CI)n%(95% CI)
Male40–491411.3(5.7–16.9)5645.2(36.4–53.9)1512.1(6.4–17.8)3225.8(18.1, 33.5)1310.5(5.1, 15.9)
50–5954.3(1.4–9.9)2925.2(17.3–33.2)4942.6(33.6–51.6)3933.9(25.3, 42.6)2421.6(14.0, 29.3)
60–6963.8(1.4–8.1)4729.9(22.8–37.1)6642.0(34.3–49.8)7749.0(41.2, 56.9)3422.7(16.0, 29.4)
70–7911.0(0.0–5.2)3331.7(22.8–40.7)4038.5(29.1–47.8)6360.6(51.2, 70.0)3031.9(22.7, 42.3)
Female40–492415.9(10.1–21.7)7851.7(43.7–59.6)1610.6(5.7–15.5)5234.4(26.9, 42.0)1610.6(5.7, 15.5)
50–5994.8(2.2–8.9)5127.1(20.8–33.5)8846.8(39.7–53.9)6836.2(29.3, 43.0)2312.4(7.6, 17.1)
60–6996.0(2.8–11.1)4530.0(22.7–37.3)7852.0(44.0–60.0)8053.3(45.3, 61.3)3121.8(15.0, 28.6)
70–7997.3(3.4–13.3)5040.3(31.7–49.0)4838.7(30.1–47.3)7862.9(54.4, 71.4)4437.3(28.6, 46.0)
Figure 2.
 
Prevalence of myopia and hyperopia in Chinese residents in Singapore, by age and sex.
Figure 2.
 
Prevalence of myopia and hyperopia in Chinese residents in Singapore, by age and sex.
Figure 3.
 
Prevalence of astigmatism and anisometropia in Chinese residents in Singapore, by age and sex.
Figure 3.
 
Prevalence of astigmatism and anisometropia in Chinese residents in Singapore, by age and sex.
 
Table 4.
 
Prevalence of Refractive Errors in Chinese Residents in Singapore, by Potential Confounders
Table 4.
 
Prevalence of Refractive Errors in Chinese Residents in Singapore, by Potential Confounders
High Myopia (< −5.0 D SE) Myopia (< −0.5 D SE) Hyperopia (>0.5 D SE) Astigmatism (< −0.5 D C) Anisometropia (>1.0 D SE diff)
n % (95% CI) n % (95% CI) n % (95% CI) n % (95% CI) n % (95% CI)
Education
None 9 3.2 (1.5–6.1) 74 26.7 (21.5–31.9) 139 50.0 (44.3–56.1) 140 50.4 (44.5, 56.2) 65 24.2 (19.0, 29.3)
Primary 20 4.5 (2.8–6.8) 124 27.8 (23.6–32.0) 175 39.3 (34.7–43.8) 201 45.2 (40.5, 49.8) 82 19.2 (15.4, 22.9)
Secondary 32 10.7 (7.2–14.2) 139 46.3 (40.7–52.0) 68 22.7 (17.9–27.4) 111 37.0 (31.5, 42.5) 45 15.5 (11.2, 19.7)
Tertiary 16 20.0 (11.9–30.4) 47 58.8 (47.2–69.6) 14 17.5 (9.9–27.6) 32 40.0 (29.2, 51.6) 20 25.0 (16.0, 35.9)
P < 0.001 P < 0.001 P < 0.001 P = 0.010 P = 0.046
Occupation
Professional and office worker 29 13.8 (9.1–18.5) 110 52.4 (45.6–59.1) 42 20.0 (14.6–25.4) 86 41.0 (34.3, 47.6) 46 22.2 (16.6, 27.9)
Salespersons 15 8.2 (4.7–13.2) 60 32.8 (26.0–39.6) 61 33.3 (26.5–40.2) 69 37.7 (30.7, 44.7) 35 19.9 (14.0, 25.8)
Production workers 14 6.1 (3.3–9.9) 79 34.2 (28.1–40.3) 84 36.4 (30.2–42.6) 106 45.9 (39.5, 52.3) 43 19.7 (14.4, 25.0)
Laborers and cleaners 5 2.6 (0.9–6.1) 49 25.9 (19.7–32.2) 85 45.0 (12.0–22.9) 81 42.9 (35.8, 49.9) 30 16.5 (11.1, 21.9)
Unemployed 2 6.1 (0.7–20.2) 11 33.3 (18.0–51.8) 14 42.4 (25.5–60.8) 15 45.5 (28.1, 63.7) 5 15.2 (5.1, 31.9)
Homemakers 12 4.6 (2.4–7.9) 78 30.0 (24.4–35.6) 110 42.3 (36.3–48.3) 130 50.0 (43.9, 56.1) 55 21.7 (16.7, 26.8)
P < 0.001 P < 0.001 P < 0.001 P = 0.157 P = 0.589
Housing
1–2 room flats 10 4.9 (2.4–8.8) 67 32.7 (26.3–39.1) 80 39.0 (32.3–45.7) 100 49.0 (42.2, 55.9) 49 25.0 (18.9, 31.1)
3 room flats 40 6.7 (4.9–9.1) 203 34.2 (30.4–38.1) 216 36.4 (32.6–40.3) 259 43.6 (39.6, 47.6) 207 18.7 (15.5, 21.9)
4–5 room flats 21 7.5 (4.7–11.2) 100 35.7 (30.1–41.3) 95 33.9 (28.4–39.5) 117 41.8 (36.0, 47.6) 50 18.3 (13.7, 22.9)
Executive flats and private housing 5 21.7 (7.5–43.7) 13 56.5 (34.5–76.8) 6 26.1 (10.2–48.4) 7 38.9 (17.3, 64.3) 6 26.1 (10.2, 48.4)
P = 0.052 P = 0.028 P = 0.559 P = 0.412 P = 0.193
Individual monthly income
Retired 3 3.0 (0.6–8.5) 26 26.0 (17.7–35.7) 40 40.0 (30.3–50.3) 45 45.0 (35.0, 55.3) 20 20.8 (13.2, 30.3)
Less than $1000 37 5.4 (3.8–7.3) 213 31.0 (27.5–34.4) 284 41.3 (37.6–45.0) 330 48.0 (44.2, 51.7) 143 21.6 (18.5, 24.8)
$1000–2000 18 9.5 (5.7–14.6) 76 40.0 (33.0–47.0) 52 27.4 (21.8–33.7) 71 37.4 (30.5, 44.2) 24 13.0 (8.1, 17.8)
$2000–3000 8 12.3 (5.5–22.8) 33 50.8 (38.1–63.4) 9 13.8 (6.5–24.7) 14 21.5 (12.3, 33.5) 9 13.8 (6.5, 24.7)
More than $3000 11 21.6 (11.3–35.3) 32 62.7 (48.1–75.9) 7 13.7 (5.7–26.3) 21 41.2 (27.6, 55.8) 13 25.5 (14.3, 39.6)
P < 0.001 P < 0.001 P < 0.001 P < 0.001 P = 0.052
Nuclear opacity (LOCS III score)
1–2 23 9.8 (6.3–14.4) 97 41.5 (35.1–47.8) 51 21.8 (16.5–27.1) 67 28.6 (22.8, 34.4)
3–4 40 5.3 (3.8–7.1) 217 28.7 (25.5–31.9) 320 42.3 (38.8–45.9) 345 45.6 (42.1, 49.2)
5–6 13 14.3 (7.8–23.2) 65 71.4 (61.0–80.4) 14 15.4 (8.7–24.5) 62 68.1 (57.5, 77.5)
P = 0.002 P < 0.001 P < 0.001 P < 0.001
Smoking
No 66 7.3 (5.7–9.2) 329 36.3 (33.3–39.4) 321 35.4 (32.3–38.5) 407 44.9 (41.7, 48.2) 178 20.3 (17.7, 23.0)
Yes 11 5.5 (2.7–9.5) 58 28.6 (22.4–34.8) 77 37.2 (31.3–44.6) 77 38.7 (31.9, 45.5) 35 18.3 (12.8, 23.7)
P = 0.550 P = 0.301 P = 0.672 P = 0.109 P = 0.511
Table 5.
 
Risk of Myopia and High Myopia among Chinese Residents in Singapore
Table 5.
 
Risk of Myopia and High Myopia among Chinese Residents in Singapore
Myopia (< −0.5 D) High Myopia (< −5.0 D)
Sex*
Females 1.20 (0.92–1.54) 1.69 (1.03–2.77)
Age*
40–49 1.00 1.00
50–59 0.37 (0.26–0.53) 0.29 (0.15–0.55)
60–69 0.45 (0.32–0.64) 0.33 (0.18–0.62)
70–81 0.60 (0.42–0.86) 0.28 (0.14–0.59)
Males, age
40–49 2.44 (1.41–4.23) 2.80 (0.97–8.04)
50–59 1.00 1.00
60–69 1.26 (0.74–2.18) 0.87 (0.26–2.94)
70–81 1.38 (0.76–2.48) 0.21 (0.02–1.85)
Females, age
40–49 2.87 (1.82–4.51) 3.76 (1.69–8.36)
50–59 1.00 1.00
60–69 1.15 (0.72–1.85) 1.27 (0.49–3.28)
70–81 1.81 (1.12–2.94) 1.55 (0.60–4.03)
Education*
None 1.00 1.00
Primary 1.26 (0.88–1.82) 1.67 (0.73–3.85)
Secondary 2.79 (1.86–4.17) 3.72 (1.61–8.62)
Tertiary 4.34 (2.46–7.68) 7.37 (2.84–19.12)
Occupation*
Professionals and office workers 1.95 (1.32–2.88) 2.01 (1.21–3.56)
Salespersons 0.89 (0.59–1.37) 1.26 (0.58–2.73)
Production operators 1.00 1.00
Laborers and cleaners 0.70 (0.45–1.09) 0.44 (0.15–1.27)
Unemployed 0.86 (0.39–1.89) 0.86 (0.18–4.06)
Homemakers 0.68 (0.44–1.06) 0.58 (0.24–1.37)
Housing*
1–2 room flats 1.00 1.00
3 room flats 1.11 (0.78–1.56) 1.39 (0.67–2.86)
4–5 room flats 1.10 (0.75–1.63) 1.40 (0.64–3.06)
Executive and private 2.29 (0.93–5.60) 3.98 (1.18–13.44)
Individual monthly income*
Retired 1.00 1.00
Less than $1000 1.15 (0.70–1.89) 1.27 (0.37–4.31)
$1000–2000 1.96 (1.10–3.49) 2.56 (0.68–9.66)
$2000–3000 2.74 (1.33–5.64) 2.81 (0.65–12.28)
More than $3000 4.51 (2.09–9.73) 5.66 (1.37–23.45)
Nuclear opacity (LOCS III score), †
1–2 1.00 1.00
3–4 1.14 (0.77–1.68) 1.62 (0.85–3.10)
5–6 10.16 (5.19–19.88) 16.04 (4.98–51.75)
Smoking, †
No 1.00 1.00
Yes 0.72 (0.51–1.05) 0.92 (0.45–1.90)
The authors thank Judy Hall, for training technical staff and providing quality assurance services; the Clinical Audit Department of the Singapore National Eye Center for data management; and Rachel Ng and Bernie Poh for coordination of community volunteer participation. 
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Table 4.
 
Prevalence of Refractive Errors in Chinese Residents in Singapore, by Potential Confounders
Table 4.
 
Prevalence of Refractive Errors in Chinese Residents in Singapore, by Potential Confounders
High Myopia (< −5.0 D SE) Myopia (< −0.5 D SE) Hyperopia (>0.5 D SE) Astigmatism (< −0.5 D C) Anisometropia (>1.0 D SE diff)
n % (95% CI) n % (95% CI) n % (95% CI) n % (95% CI) n % (95% CI)
Education
None 9 3.2 (1.5–6.1) 74 26.7 (21.5–31.9) 139 50.0 (44.3–56.1) 140 50.4 (44.5, 56.2) 65 24.2 (19.0, 29.3)
Primary 20 4.5 (2.8–6.8) 124 27.8 (23.6–32.0) 175 39.3 (34.7–43.8) 201 45.2 (40.5, 49.8) 82 19.2 (15.4, 22.9)
Secondary 32 10.7 (7.2–14.2) 139 46.3 (40.7–52.0) 68 22.7 (17.9–27.4) 111 37.0 (31.5, 42.5) 45 15.5 (11.2, 19.7)
Tertiary 16 20.0 (11.9–30.4) 47 58.8 (47.2–69.6) 14 17.5 (9.9–27.6) 32 40.0 (29.2, 51.6) 20 25.0 (16.0, 35.9)
P < 0.001 P < 0.001 P < 0.001 P = 0.010 P = 0.046
Occupation
Professional and office worker 29 13.8 (9.1–18.5) 110 52.4 (45.6–59.1) 42 20.0 (14.6–25.4) 86 41.0 (34.3, 47.6) 46 22.2 (16.6, 27.9)
Salespersons 15 8.2 (4.7–13.2) 60 32.8 (26.0–39.6) 61 33.3 (26.5–40.2) 69 37.7 (30.7, 44.7) 35 19.9 (14.0, 25.8)
Production workers 14 6.1 (3.3–9.9) 79 34.2 (28.1–40.3) 84 36.4 (30.2–42.6) 106 45.9 (39.5, 52.3) 43 19.7 (14.4, 25.0)
Laborers and cleaners 5 2.6 (0.9–6.1) 49 25.9 (19.7–32.2) 85 45.0 (12.0–22.9) 81 42.9 (35.8, 49.9) 30 16.5 (11.1, 21.9)
Unemployed 2 6.1 (0.7–20.2) 11 33.3 (18.0–51.8) 14 42.4 (25.5–60.8) 15 45.5 (28.1, 63.7) 5 15.2 (5.1, 31.9)
Homemakers 12 4.6 (2.4–7.9) 78 30.0 (24.4–35.6) 110 42.3 (36.3–48.3) 130 50.0 (43.9, 56.1) 55 21.7 (16.7, 26.8)
P < 0.001 P < 0.001 P < 0.001 P = 0.157 P = 0.589
Housing
1–2 room flats 10 4.9 (2.4–8.8) 67 32.7 (26.3–39.1) 80 39.0 (32.3–45.7) 100 49.0 (42.2, 55.9) 49 25.0 (18.9, 31.1)
3 room flats 40 6.7 (4.9–9.1) 203 34.2 (30.4–38.1) 216 36.4 (32.6–40.3) 259 43.6 (39.6, 47.6) 207 18.7 (15.5, 21.9)
4–5 room flats 21 7.5 (4.7–11.2) 100 35.7 (30.1–41.3) 95 33.9 (28.4–39.5) 117 41.8 (36.0, 47.6) 50 18.3 (13.7, 22.9)
Executive flats and private housing 5 21.7 (7.5–43.7) 13 56.5 (34.5–76.8) 6 26.1 (10.2–48.4) 7 38.9 (17.3, 64.3) 6 26.1 (10.2, 48.4)
P = 0.052 P = 0.028 P = 0.559 P = 0.412 P = 0.193
Individual monthly income
Retired 3 3.0 (0.6–8.5) 26 26.0 (17.7–35.7) 40 40.0 (30.3–50.3) 45 45.0 (35.0, 55.3) 20 20.8 (13.2, 30.3)
Less than $1000 37 5.4 (3.8–7.3) 213 31.0 (27.5–34.4) 284 41.3 (37.6–45.0) 330 48.0 (44.2, 51.7) 143 21.6 (18.5, 24.8)
$1000–2000 18 9.5 (5.7–14.6) 76 40.0 (33.0–47.0) 52 27.4 (21.8–33.7) 71 37.4 (30.5, 44.2) 24 13.0 (8.1, 17.8)
$2000–3000 8 12.3 (5.5–22.8) 33 50.8 (38.1–63.4) 9 13.8 (6.5–24.7) 14 21.5 (12.3, 33.5) 9 13.8 (6.5, 24.7)
More than $3000 11 21.6 (11.3–35.3) 32 62.7 (48.1–75.9) 7 13.7 (5.7–26.3) 21 41.2 (27.6, 55.8) 13 25.5 (14.3, 39.6)
P < 0.001 P < 0.001 P < 0.001 P < 0.001 P = 0.052
Nuclear opacity (LOCS III score)
1–2 23 9.8 (6.3–14.4) 97 41.5 (35.1–47.8) 51 21.8 (16.5–27.1) 67 28.6 (22.8, 34.4)
3–4 40 5.3 (3.8–7.1) 217 28.7 (25.5–31.9) 320 42.3 (38.8–45.9) 345 45.6 (42.1, 49.2)
5–6 13 14.3 (7.8–23.2) 65 71.4 (61.0–80.4) 14 15.4 (8.7–24.5) 62 68.1 (57.5, 77.5)
P = 0.002 P < 0.001 P < 0.001 P < 0.001
Smoking
No 66 7.3 (5.7–9.2) 329 36.3 (33.3–39.4) 321 35.4 (32.3–38.5) 407 44.9 (41.7, 48.2) 178 20.3 (17.7, 23.0)
Yes 11 5.5 (2.7–9.5) 58 28.6 (22.4–34.8) 77 37.2 (31.3–44.6) 77 38.7 (31.9, 45.5) 35 18.3 (12.8, 23.7)
P = 0.550 P = 0.301 P = 0.672 P = 0.109 P = 0.511
Table 5.
 
Risk of Myopia and High Myopia among Chinese Residents in Singapore
Table 5.
 
Risk of Myopia and High Myopia among Chinese Residents in Singapore
Myopia (< −0.5 D) High Myopia (< −5.0 D)
Sex*
Females 1.20 (0.92–1.54) 1.69 (1.03–2.77)
Age*
40–49 1.00 1.00
50–59 0.37 (0.26–0.53) 0.29 (0.15–0.55)
60–69 0.45 (0.32–0.64) 0.33 (0.18–0.62)
70–81 0.60 (0.42–0.86) 0.28 (0.14–0.59)
Males, age
40–49 2.44 (1.41–4.23) 2.80 (0.97–8.04)
50–59 1.00 1.00
60–69 1.26 (0.74–2.18) 0.87 (0.26–2.94)
70–81 1.38 (0.76–2.48) 0.21 (0.02–1.85)
Females, age
40–49 2.87 (1.82–4.51) 3.76 (1.69–8.36)
50–59 1.00 1.00
60–69 1.15 (0.72–1.85) 1.27 (0.49–3.28)
70–81 1.81 (1.12–2.94) 1.55 (0.60–4.03)
Education*
None 1.00 1.00
Primary 1.26 (0.88–1.82) 1.67 (0.73–3.85)
Secondary 2.79 (1.86–4.17) 3.72 (1.61–8.62)
Tertiary 4.34 (2.46–7.68) 7.37 (2.84–19.12)
Occupation*
Professionals and office workers 1.95 (1.32–2.88) 2.01 (1.21–3.56)
Salespersons 0.89 (0.59–1.37) 1.26 (0.58–2.73)
Production operators 1.00 1.00
Laborers and cleaners 0.70 (0.45–1.09) 0.44 (0.15–1.27)
Unemployed 0.86 (0.39–1.89) 0.86 (0.18–4.06)
Homemakers 0.68 (0.44–1.06) 0.58 (0.24–1.37)
Housing*
1–2 room flats 1.00 1.00
3 room flats 1.11 (0.78–1.56) 1.39 (0.67–2.86)
4–5 room flats 1.10 (0.75–1.63) 1.40 (0.64–3.06)
Executive and private 2.29 (0.93–5.60) 3.98 (1.18–13.44)
Individual monthly income*
Retired 1.00 1.00
Less than $1000 1.15 (0.70–1.89) 1.27 (0.37–4.31)
$1000–2000 1.96 (1.10–3.49) 2.56 (0.68–9.66)
$2000–3000 2.74 (1.33–5.64) 2.81 (0.65–12.28)
More than $3000 4.51 (2.09–9.73) 5.66 (1.37–23.45)
Nuclear opacity (LOCS III score), †
1–2 1.00 1.00
3–4 1.14 (0.77–1.68) 1.62 (0.85–3.10)
5–6 10.16 (5.19–19.88) 16.04 (4.98–51.75)
Smoking, †
No 1.00 1.00
Yes 0.72 (0.51–1.05) 0.92 (0.45–1.90)
×
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