***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 errors and their distribution according to age and sex in a Brazilian population . METHODS This population -based cross-sectional study involved 7654 Brazilian inhabitants of nine municipalities of Sao Paulo State , Brazil , between March 2004 and July 2005 . Participants aged > 1 year were selected using a r and om , stratified , household cluster sampling technique , excluding individuals with previous refractive or cataract surgery . Myopia was defined as spherical equivalent ( SE ) ≤-0.5D , high myopia as SE ≤-3.0D , hyperopia as SE ≥+0.5D , high hyperopia as SE ≥+3D , astigmatism as ≤-0.5DC and anisometropia as ≥1.0D difference between eyes . Age , sex , complaints and a comprehensive eye examination including cycloplegic refraction test were collected and analysed using descriptive analysis , univariate and multivariate methods . RESULTS The prevalence of astigmatism was 59.7 % , hyperopia 33.8 % and myopia was 25.3 % . Astigmatism had a progressive increase with age . With-the-rule ( WTR ) axes of astigmatism were more frequently observed in the young participants and the against-the-rule ( ATR ) axes were more frequent in the older subjects . The onset of myopia occurred more frequently between the 2nd and 3rd decades of life . Anisometropia showed a prevalence of 13.2 % ( 95 % CI 12.4 - 13.9 ; p < 0.001 ) . There was an association between age and all types of refractive error and hyperopia was also associated with sex . Hyperopia was associated with WTR axes ( odds ratio 0.73 ; 95 % CI : 0.6 - 0.8 ; p < 0.001 ) and myopia with ATR axes ( odds ratio 0.66 ; 95 % CI : 0.6 - 0.8 ; p < 0.001 ) . CONCLUSIONS Astigmatism was the most prevalent refractive error in a Brazilian population . There was a strong relationship between age and all refractive errors and between hyperopia and sex . WTR astigmatism was more frequently associated with hyperopia and ATR astigmatism with myopia . The vast majority of participants had low- grade refractive error , which favours planning aim ed at correction of refractive error in the population PURPOSE To describe the prevalence of hyperopia and associated factors in a representative sample of Australian schoolchildren 6 and 12 years old . DESIGN Population -based cross-sectional study . PARTICIPANTS Schoolchildren ages 6 ( n = 1765 ) and 12 ( n = 2353 ) from 55 r and omly selected schools across Sydney . METHODS Detailed eye examinations included  cycloplegic autorefraction , ocular biometry , cover testing , and dilated fundus examination .  Information on birth and medical history were obtained from a parent question naire . MAIN OUTCOME MEASURES Moderate hyperopia defined as spherical equivalent ( SE ) refraction of > or = + 2.00 diopters ( D ) , and eye conditions including amblyopia , strabismus , astigmatism , and anisometropia . RESULTS Prevalences of moderate hyperopia among children ages 6 and 12 were 13.2 % and 5.0 % , respectively ; it was more frequent in children of Caucasian ethnicity ( 15.7 % and 6.8 % , respectively ) than in children of other ethnic groups . Compared with children without significant ametropia ( -0.49 < or = SE refraction < or = + 1.99 D ) , the prevalence of eye conditions including amblyopia , strabismus , abnormal convergence , and reduced stereoacuity was significantly greater in children with moderate hyperopia ( all Ps < 0.01 ) . Maternal smoking was significantly associated with moderate hyperopia among 6-year-olds ( P = 0.03 ) , but this association was borderline among 12-year-olds ( P = 0.055 ) . Early gestational age ( < 37 weeks ) and low birth weight ( < 2500 g ) were not statistically significant predictors of moderate hyperopia in childhood . CONCLUSIONS Moderate hyperopia was strongly associated with many common eye conditions , particularly amblyopia and strabismus , in older children . Birth parameters did not predict moderate hyperopia 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 Background Due to its high prevalence and associated sight-threatening pathologies , myopia has emerged as a major health issue in East Asia . The purpose was to test the impact on myopia development of a school-based intervention program aim ed at increasing the time student spent outdoors . Methods A total of 3051 students of two primary ( grade s 1 - 5 , aged 6 - 11 ) and two junior high schools ( grade s 7 - 8 , aged 12 - 14 ) in both urban and rural Northeast China were enrolled . The  intervention group ( n = 1735 ) unlike the control group ( n = 1316 ) was allowed two additional 20-min recess programs outside the classroom . A detailed question naire was administered to parents and children . Uncorrected visual acuity ( UCVA ) was measured using an E St and ard Logarithm Vision Acuity Chart ( GB11533 - 2011 ) at baseline , 6-month and 1-year intervals . A r and om sub sample ( n = 391 ) participated in the clinic visits and underwent  cycloplegia  at the beginning and after 1 year . Results The mean UCVA for the entire intervention group was significantly better than the entire control group after 1 year ( P < 0.001 ) . In the subgroup study , new onset of myopia and changes in refractive error towards myopia were direction during the study period was significantly lower in the intervention group than in the control group ( 3.70 % vs. 8.50 % , P = 0.048 ; -0.10 ± 0.65 D/year vs. -0.27 ± 0.52 D/year , P = 0.005 ) . Changes in axial length and IOP were also significantly lower following the intervention group ( 0.16 ± 0.30 mm/year vs. 0.21 ± 0.21 mm/year , P = 0.034 ; -0.05 ± 2.78 mmHg/year vs. 0.67 ± 2.21 mmHg/year , P = 0.006 ) . Conclusions Increasing outdoor activities prevented myopia onset and development , as well as axial growth and elevated IOP in children . Trial registration Current controlled trials NCT02271373 Purpose : To determine the prevalence of amblyopia and refractive errors among 7 to 12-year-old primary school children in Tehran , Iran . Methods : This population -based cross-sectional study included 2,410 r and omly selected students .  Visual acuity was tested using an E-chart on Yang vision tester .  Refractive errors were measured by photorefractometry and cycloautorefraction . Strabismus was checked using cover test . Direct ophthalmoscopy  was used to assess the anterior segment , lens opacities , red reflex and fundus . Functional amblyopia was defined as best corrected visual acuity ≤20/40 in one or both eyes with no anatomical problems . Results : Amblyopia was present in 2.3 % ( 95 % CI : 1.8 % to 2.9 % ) of participants with no difference between the genders . Amblyopic subjects were significantly younger than non-amblyopic children ( P=0.004 ) . Overall , 15.9 % of hyperopic and 5.9 % of myopic cases had amblyopia . The prevalence of hyperopia ≥+2.00D , myopia ≤-0.50D , astigmatism ≥0.75D , and anisometropia ( ≥1.00D ) was 3.5 % , 4.9 % , 22.6 % , and 3.9 % , respectively . With increasing age , the prevalence of myopia increased ( P<0.001 ) , that of hyperopia decreased ( P=0.007 ) , but astigmatism showed no change . Strabismus was found in 2.3 % of cases . Strabismus ( OR=17.9 ) and refractive errors , especially anisometropia ( OR=12.87 ) and hyperopia ( OR=11.87 ) , were important amblyogenic risk factors . Conclusion : The high prevalence of amblyopia in our subjects in comparison to developed countries reveals the necessity of timely and sensitive screening methods . Due to the high prevalence of amblyopia among children with refractive errors , particularly high hyperopia and anisometropia , provision of glasses should be specifically attended by parents and supported by the Ministry of Health and insurance organizations INTRODUCTION Refractive error remains one of the primary causes of visual impairment in children worldwide , and the prevalence of refractive error varies widely . The objective of this study was to determine the prevalence of refractive error and study the possible associated factors inducing refractive error among primary school children of Malay ethnicity in the suburban area of Kota Bharu , Kelantan , Malaysia . MATERIAL S AND METHODS A school-based cross-sectional study was performed from January to July 2006 by r and om selection on St and ard 1 to St and ard 6 students of 10 primary schools in the Kota Bharu district .  Visual acuity  assessment was measured using logMAR ETDRS chart . Positive predictive value of uncorrected visual acuity equal or worse than 20/40 , was used as a cut-off point for further evaluation by automated refraction and retinoscopic refraction . RESULTS A total of 840 students were enumerated but only 705 were examined . The prevalence of uncorrected visual impairment was seen in 54 ( 7.7 % ) children . The main cause of the uncorrected visual impairment was refractive error which contributed to 90.7 % of the total , and with 7.0 % prevalence for the studied population . Myopia is the most common type of refractive error among children aged 6 to 12 years with prevalence of 5.4 % , followed by hyperopia at 1.0 % and astigmatism at 0.6 % . A significant positive correlation was noted between myopia development with increasing age ( P < 0.005 ) , more hours spent on reading books ( P < 0.005 ) and background history of siblings with glasses ( P < 0.005 ) and whose parents are of higher educational level ( P < 0.005 ) . Malays in suburban Kelantan ( 5.4 % ) have the lowest prevalence of myop 
    Output:
    
Conclusion This report showed that astigmatism was the most common refractive errors in children and adults followed by hyperopia and myopia .
The highest prevalence of myopia and astigmatism was seen in South-East Asian adults .