***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: PURPOSE To determine the prevalence of refractive error types in Singaporean Chinese children aged 6 to 72 months . METHODS The Strabismus , Amblyopia and Refractive Error in Singaporean Children ( STARS ) is a population -based study in southwest Singapore . Door-to-door recruitment of participants was used , with disproportionate r and om sampling in 6-month increments . Parental question naires were administered . Participant eye examinations included  logMAR visual acuity , cycloplegic autorefraction , and ocular biometry .  Overall and age-specific prevalences of myopia ( spherical equivalence [ SE ] < or= -0.50 D ) , high myopia ( SE < or= -6.00 D ) , hyperopia ( SE > or= + 3.00 D ) , astigmatism ( cylinder > or= + 1.50 D ) , and anisometropia ( SE difference between each eye > or=2.00 D ) were calculated . RESULTS A total of 3009 children were examined ( participation rate , 72.3 % ) . Right eye ( OD ) cycloplegia data were available for 1375 boys and 1264 girls ( mean age , 41 months ) . Mean OD SE was + 0.69 D ( SD 1.15 ) . Overall myopia prevalence was 11.0 % with no variance between the sexes ( P = 0.91 ) . The prevalence of high myopia ( at least -6.00 D ) was 0.2 % . The prevalences of hyperopia , astigmatism , and anisometropia were 1.4 % , 8.6 % , and 0.6 % , respectively . Most astigmatism ( > 95 % ) was with-the-rule ( cylinder axes between 1 degrees and 15 degrees or 165 degrees and 180 degrees ) . Myopia was present in 15.8 % , 14.9 % , 20.2 % , 8.6 % , 7.6 % , and 6.4 % of children aged 6 to 11 , 12 to 23 , 24 to 35 , 36 to 47 , 48 to 59 , and 60 to 72 months , respectively . Prevalence increased with age for astigmatism ( P < 0.001 ) , but not for hyperopia or anisometropia ( P = 0.55 and P = 0.37 ) , respectively . CONCLUSIONS The prevalences of myopia and astigmatism in young Singaporean Chinese children are high , but that of hyperopia is low . Age effects were observed for each refractive error category , but differences between the sexes were not significant . Age-related variation in myopia prevalence may be influenced by ocular development , environment , and /or testability PURPOSE To describe the methodology , sampling strategy and preliminary results for the Aston Eye Study ( AES ) , a cross-sectional study to determine the prevalence of refractive error and its associated ocular biometry in a large multi-racial sample of school children from the metropolitan area of Birmingham , Engl and . METHODS A target sample of 1700 children aged 6 - 7 years and 1200 aged 12 - 13 years is being selected from Birmingham schools selected r and omly with stratification by area deprivation index ( a measure of socio-economic status ) . Schools with pupils predominantly ( > 70 % ) from a single race are excluded . Sample size calculations account for the likely participation rate and the clustering of individuals within schools . Procedures involve st and ardised protocol s to allow for comparison with international population -based data .  Visual acuity , non-contact ocular biometry ( axial length , corneal radius of curvature and anterior chamber depth ) and cycloplegic autorefraction  are measured in both eyes . Distance and near oculomotor balance , height and weight are also assessed . Question naires for parents and older children will allow the influence of environmental factors on refractive error to be examined . RESULTS Recruitment and data collection are ongoing ( currently N=655 ) . Preliminary cross-sectional data on 213 South Asian , 44 black African Caribbean and 70 white European children aged 6 - 7 years and 114 South Asian , 40 black African Caribbean and 115 white European children aged 12 - 13 years found myopia prevalence of 9.4 % and 29.4 % for the two age groups respectively . A more negative mean spherical equivalent refraction ( SER ) was observed in older children ( -0.21 D vs + 0.87 D ) . Ethnic differences in myopia prevalence are emerging with South Asian children having higher levels than white European children 36.8 % vs 18.6 % ( for the older children ) . Axial length , corneal radius of curvature and anterior chamber depth were normally distributed , while SER was leptokurtic ( p<0.001 ) with a slight negative skew . CONCLUSIONS The AES will allow ethnic differences in the ocular characteristics of children from a large metropolitan area of the UK to be examined . The findings to date indicate the emergence of higher levels of myopia by early adolescence in second and third generation British South Asians , compared to white European children . The continuation of the AES will allow the early determinants of these ethnic differences to be studied PURPOSE To determine the risk factors of incident myopia in a school-based cohort study in Singaporean children . METHODS A 3-year prospect i ve cohort study was conducted in Singaporean school children aged 7 to 9 years in three schools at entry . Chinese children without myopia at baseline ( n = 994 ) were included in the analysis . The main outcome was incident myopia , defined as spherical equivalent ( SE ) at least -0.75 D based on cycloplegic autorefraction . Other definitions of incident myopia , at least -0.5 D and at least -1.0 D , were also assessed . RESULTS After controlling for school , age , gender , income , reading in books per week and intelligence quotient ( IQ ) test scores , we found the relative risk ( RR ) of incident myopia defined as -0.75 D to be 1.55 ( 95 % confidence interval [ CI ] 1.18 - 2.04 ) for two versus no myopic parents . The multivariate RR of myopia for IQ in the third versus first tertile was 1.50 ( 95 % CI , 1.19 - 1.89 ) . However , the RR of incident myopia was 1.01 ( 95 % CI , 0.97 - 1.05 ) for every unit increase in books read per week . Similar results were obtained with definitions of -0.5 and -1.0 D for incident myopia . CONCLUSIONS These data provide new prospect i ve evidence of essential links between parental myopia , IQ scores and subsequent myopia development . However , reading in books per week was not associated with incident myopia PURPOSE To investigate the hypothesis that the excessive growth of the eye in myopia is associated with general growth and thus influenced by early life biological and social factors , and that these associations underlie recent secular trends of increasing prevalence and severity of myopia . DESIGN Cohort study . PARTICIPANTS A total of 2487 r and omly selected 44-year-old members of the 1958 British birth cohort ( 27 % sub sample ) . METHODS Diverse and detailed biological , social , and lifestyle data have been collected by following members since birth through a series of clinical examinations or face-to-face interviews carried out by trained examiners . At 44 years , cohort members underwent autorefraction using the Nikon Retinomax 2 ( Nikon Corp. , Tokyo , Japan ) under non-cycloplegic conditions . A lifecourse epidemiologic approach , based on 4 sequential multivariable " life stage " models ( preconceptional ; prenatal , perinatal , and postnatal ; childhood ; and adult ) , was used to examine the influence of early life biological , social and lifestyle factors , growth patterns , and " eye-specific " factors on myopia . MAIN OUTCOME MEASURES Myopia severity ( all , mild/moderate : spherical equivalent -0.75 to -5.99 diopters [ D ] ; severe : ≥-6.00 D extreme vs. emmetropia -0.74 to + 0.99 D ) and myopia onset ( early [ < 16 years ] vs. later ) . RESULTS A total of 1214 individuals ( 49 % ; 95 % confidence interval , 48.8 - 50.8 ) were myopic ( late onset in 979 [ 80.6 % ] ) . Myopia was positively associated with low birthweight for gestational age , gender , greater maternal age , higher paternal occupational social class , and maternal smoking in early pregnancy . Myopia was independently associated with proxy markers of near work and educational performance , with some differences by onset and severity . In adults , greater height and higher educational attainment and socioeconomic status were associated with myopia . CONCLUSIONS Trends in the key influences on child health and growth identified as novel putative risk factors in this study are consistent with global trends of increasing myopia : increasing births to older mothers , increasing rates of intrauterine growth retardation and survival of affected children , increasing persistence of smoking in pregnancy , and changing socioeconomic status . Prospect s for prevention of myopia would be improved by a paradigm shift in myopia research , with lifecourse and genetic epidemiologic approaches applied in t and  em  in large unselected population We aim ed to identify the prevalence and risk factors of myopia among secondary -school students in Amman . Thus 1777 ( 1081 males and 696 females ) students aged 12 - 17 years old were recruited from 8 schools r and omly selected from 8 different geographic locations in Amman .  Data were collected by question naire , and self-reported myopia was checked against school medical records . The prevalence of myopia was 17.6 % , with no significant difference between males and females after adjusting for other possible variables . Myopia was significantly associated with age , family history of myopia , computer use , and reading and writing outside school . Playing sports was inversely associated with myopia but there was no association with watching television OBJECTIVE To assess the relationship of near , midworking distance , and outdoor activities with prevalence of  myopia in school-aged children . DESIGN Cross-sectional study of 2 age sample s from 51 Sydney schools , selected using a r and om cluster design . PARTICIPANTS One thous and seven hundred sixty-five 6-year-olds ( year 1 ) and 2367 12-year-olds ( year 7 ) participated in the Sydney Myopia Study from 2003 to 2005 . METHODS Children had a comprehensive eye examination , including cycloplegic refraction . Parents and children completed detailed question naires on activity . MAIN OUTCOME MEASURES Myopia prevalence and mean spherical equivalent ( SE ) in relation to patterns of near , midworking distance , and outdoor activities .  Myopia was defined as SE refraction < or = -0.5 diopters ( D ) . RESULTS Higher levels of outdoor activity ( sport and leisure activities ) were associated with more hyperopic refractions and lower myopia prevalence in the 12-year-old students . Students who combined high levels of near work with low levels of outdoor activity had the least hyperopic mean refraction ( + 0.27 D ; 95 % confidence interval [ CI ] , 0.02 - 0.52 ) , whereas students who combined low levels of near work with high levels of outdoor activity had the most hyperopic mean refraction ( + 0.56 D ; 95 % CI , 0.38 - 0.75 ) . Significant protective associations with increased outdoor activity were seen for the lowest ( P = 0.04 ) and middle ( P = 0.02 ) tertiles of near-work activity . The lowest odds ratios for myopia , after adjusting for confounders , were found in groups reporting the highest levels of outdoor activity . There were no associations between indoor sport and myopia . No consistent associations between refraction and measures of activity were seen in the 6-year-old sample . CONCLUSIONS Higher levels of total time spent outdoors , rather than sport per se , were associated with less myopia and a more hyperopic mean refraction , after adjusting for near work , parental myopia , and ethnicity BACKGROUND Refractive error is an important cause of preventable visual impairment and blindness worldwide . Population -based studies will continue to be a key part in identification ofthe magnitude and the importance of this common eye disease . OBJECTIVE To assess the prevalence of the refractive error in primary school-aged children in Bangkok and Nakhonpathom together with the provision of the appropriately free of charge spectacles . MATERIAL AND METHOD A Population -based cross-sectional analytic study was conducted between October 2008 and September 2009 . R and om selection of geographically defined clusters was used to identify the study sample . The examination included  visual acuity ( VA ) by Snellen chart and pinhole correction , autorefraction under cycloplegic refraction , ocular motility evaluation , examination of the external eye , anterior segment , media , and fundus . Ophthalmologists screened for ocular abnormalities . RESULTS Among 2340 children , 1100 in Bangkok and 1240 in Nakhonpathom were examined The prevalence of refractive error in Bangkok and Nakhornpathom were 12.7 % and 5.7 % respectively . Refractive error was the cause in 97.6 % of eyes with reduced vision , amblyopia in 0.5 % 
    Output:
    
Marked ethnic differences in age-specific prevalence of myopia exist .