***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: A prospect i ve study of routine school vision tests in 1809 children aged 8 and 10 y was undertaken in schools in the Cambridge Health District over two years ( 1988 - 1990 ) to establish whether a significant number of defects of vision were detected . Although the visual acuity of 31 % of children who had an abnormal test was recorded as abnormal , most abnormalities were minimal . Only 15 ( 0.83 % ) had newly diagnosed problems requiring treatment . Almost all children with marked visual abnormalities had already been detected before school entry , at the 5 y school vision test or on another occasion . Near vision testing did not identify any previously undiagnosed child with significant defects who did not also have distant vision abnormalities . Satisfactory colour vision test results had been recorded for most children at the 5 y school entry vision test . These data do not justify the continued use of routine screening in junior schools PURPOSE To assess the prevalence of refractive errors and vision impairment in school-age children in Shunyi District , northeast of Beijing , the Peoples Republic of China . METHODS R and om selection of village-based clusters was used to identify a sample of children 5 to 15 years of age .  Resident registration books were used to enumerate eligible children in the selected villages and identify their current school . Ophthalmic examinations were conducted in 132 schools on children from 29 clusters during May 1988 to July 1998 , including  visual acuity measurements , cycloplegic retinoscopy , cycloplegic autorefraction , ocular motility evaluation , and examination of the external eye , anterior segment , media , and fundus .  Independent replicate measurements of all children with reduced vision and a sample of those with normal vision were done for quality assurance monitoring in three schools . RESULTS A total of 6,134 children from 4,338 households were enumerated , and 5,884 children ( 95.9 % ) were examined . The prevalence of uncorrected , presenting , and best visual acuity 0.5 ( 20/40 ) or worse in at least one eye was 12.8 % , 10.9 % , and 1.8 % , respectively ; 0.4 % had best visual acuity 0.5 or worse in both eyes . Refractive error was the cause in 89.5 % of the 1,236 eyes with reduced vision  , amblyopia in 5 % , other causes in 1.5 % , with unexplained causes in the remaining 4 % . Myopia -0.5 diopter or less in either eye was essentially absent in 5-year-old children , but increased to 36.7 % in males and 55.0 % in females by age 15 . Over this same age range , hyperopia 2 diopters or greater decreased from 8.8 % in males and 19.6 % in females to less than 2 % in both . Females had a significantly higher risk of both myopia and hyperopia . CONCLUSIONS Reduced vision because of myopia is an important public health problem in school-age children in Shunyi District . More than 9 % of children could benefit from prescription glasses . Further studies are needed to determine whether the upward trend in the prevalence of myopia continues far beyond age 15 and whether the development of myopia is changing for more recent birth cohorts UNLABELLED A prospect i ve 2-year study on myopia progression was commenced in 1984/85 , with special attention to the rate of progression in a representative group of school children aged 9 to 12 years . A follow-up investigation of this group of myopic persons ( now aged 17 - 20 years ) was performed after 8 years , in order to describe the refractive error and possible risk factors for myopia progression over the period . The refractive error increased from -2.77 D to -5.14 D ( mean values ) . PARAMETERS age at début , degree of myopia , intraocular pressure , changes at the fundus , status of phoria , nearpoint of convergence and accommodation were all measured at the start and related to the refractive error measured 8 years later . No single parameter , apart from age at début , indicated that the individual would reach a high degree of myopia . The refractive error among the children with a début below 7 years of age was -6.60 D , but only -3.72 D among those with a début after 10 years . The change in refractive error over the 8-year period was not statistically related to the age at début , neither did the rate of progression depend on the degree of myopia , the changes at the fundus , nor the intraocular pressure . However , children could be found who had a high rate of progression , by using a combination of these parameters PURPOSE To assess the prevalence of refractive error and related visual impairment in school-aged children in the rural population of the Mahabubnagar district in the southern Indian state of And hra Pradesh . METHODS R and om selection of village-based clusters was used to identify a sample of children 7 to 15 years of age . From April 2000 through February 2001 , children in the 25 selected clusters were enumerated in a door-to-door survey and examined at a rural eye center in the district . The examination included  visual acuity measurements , ocular motility evaluation , retinoscopy and autorefraction under cycloplegia , and examination of the anterior segment , media , and fundus .  Myopia was defined as spherical equivalent refractive error of at least -0.50 D and hyperopia as + 2.00 D or more . Children with reduced vision and a sample of those with normal vision underwent independent replicate examinations for quality assurance in seven clusters . RESULTS A total of 4414 children from 4876 households was enumerated , and 4074 ( 92.3 % ) were examined . The prevalence of uncorrected , baseline ( presenting ) , and best corrected visual acuity of 20/40 or worse in the better eye was 2.7 % , 2.6 % , and 0.78 % , respectively . Refractive error was the cause in 61 % of eyes with vision impairment , amblyopia in 12 % , other causes in 15 % , and unexplained causes in the remaining 13 % . A gradual shift toward less-positive values of refractive error occurred with increasing age in both boys and girls . Myopia in one or both eyes was present in 4.1 % of the children . Myopia risk was associated with female gender and having a father with a higher level of schooling . Higher risk of myopia in children of older age was of borderline statistical significance ( P = 0.069 ) . Hyperopia in at least one eye was present in 0.8 % of children , with no significant predictors . CONCLUSIONS Refractive error was the main cause of visual impairment in children aged between 7 and 15 years in rural India . There was a benefit of spectacles in 70 % of those who had visual acuity of 20/40 or worse in the better eye at baseline examination . Because visual impairment can have a significant impact on a child 's life in terms of education and development , it is important that effective strategies be developed to eliminate this easily treated cause of visual impairment PURPOSE To assess the prevalence of refractive error and related visual impairment in school-aged children in an urban population in New Delhi , India . METHODS R and om selection of geographically defined clusters was used to identify a sample of children 5 to 15 years of age . From December 2000 through March 2001 , children in 22 selected clusters were enumerated through a door-to-door survey and examined at a local facility . The examination included  visual acuity measurements , ocular motility evaluation , retinoscopy and autorefraction under cycloplegia , and examination of the anterior segment , media , and fundus .  Myopia was defined as spherical equivalent refractive error of at least -0.50 D and hyperopia as + 2.00 D or more . Children with reduced vision and a sample of those with normal vision underwent independent replicate examinations for quality assurance in four of the clusters . RESULTS A total of 7008 children from 3426 households were enumerated , and 6447 ( 92.0 % ) examined . The prevalence of uncorrected , baseline ( presenting ) , and best corrected visual acuity of 20/40 or worse in the better eye was 6.4 % , 4.9 % , and 0.81 % , respectively . Refractive error was the cause in 81.7 % of eyes with vision impairment , amblyopia in 4.4 % , retinal disorders in 4.7 % , other causes in 3.3 % , and unexplained causes in the remaining 5.9 % . There was an age-related shift in refractive error from hyperopia in young children ( 15.6 % in 5-year-olds ) toward myopia in older children ( 10.8 % in 15-year-olds ) . Overall , hyperopia was present in 7.7 % of children and myopia in 7.4 % . Hyperopia was associated with female gender . Myopia was more common in children of fathers with higher levels of education . CONCLUSIONS Reduced vision because of uncorrected refractive error is a major public health problem in urban school-aged children in India . Cost-effective strategies are needed to eliminate this easily treated cause of vision impairment In a sample of children used to assess the value of optical correction of hypermetropia from the age of 6 months the refraction of the most hypermetropic meridian frequently became less than 3.5 D as the children grew . When this occurred , the incidence of squint was significantly less ( p less than 0.001 ) and the last known acuity after treatment was significantly better ( p less than 0.001 ) than when it did not . This process of emmetropisation appears to have been impeded by the consistent wearing of hypermetropic spectacle correction from the age of 6 months PURPOSE To assess results of a vision screening programme in schools in India , 5 years after its introduction . MATERIAL Question naires on school eye screening activities were sent to 200 r and omly selected districts . METHODS Data from 61 districts were analysed , using process indicators to assess performance at different stages of the screening procedure . RESULTS Teachers screened 5.39 million children in 61 districts . Refraction was done on 205,082 children ( 3.8 % ) and 43,922 children ( 0.8 % ) were provided with spectacles .  Children of 10 - 15 years have more refractive errors . Different stages in the procedure are evaluated . CONCLUSION Vision screening in schools has been taken up successfully in many districts in India . This has reduced the workload of eye care staff and increased the coverage . The simplicity of the procedure facilitates widespread application . Many parents take their children to the private sector for services . Monitoring and reporting needs to be improved PURPOSE To assess the prevalence of refractive error and vision impairment in school age children in the terai area of the Mechi zone in Eastern Nepal . METHODS R and om selection of village-based clusters was used to identify a sample of children 5 to 15 years of age . Children in the 25 selected clusters were enumerated through a door-to-door household survey and invited to village sites for examination .  Visual acuity measurements , cycloplegic retinoscopy , cycloplegic autorefraction , ocular motility evaluation , and anterior segment , media , and fundus examinations  were done from May 1998 through July 1998 . Independent replicate examinations for quality assurance monitoring took place in all children with reduced vision and in a sample of those with normal vision in seven villages . RESULTS A total of 5,526 children from 3,724 households were enumerated , and 5,067 children ( 91.7 % ) were examined . The prevalence of uncorrected , presenting , and best visual acuity 0.5 ( 20/40 ) or worse in at least one eye was 2.9 % , 2.8 % , and 1.4 % , respectively ; 0.4 % had best visual acuity 0.5 or worse in both eyes . Refractive error was the cause in 56 % of the 200 eyes with reduced uncorrected vision , amblyopia in 9 % , other causes in 19 % , with unexplained causes in the remaining 16 % . Myopia -0.5 diopter or less in either eye or hyperopia 2 diopters or greater was observed in less than 3 % of children . Hyperopia risk was associated with female gender and myopia risk with older age . CONCLUSIONS The prevalence of reduced vision is very low in school-age children in Nepal , most of it because of correctable refractive error . Further studies are needed to determine whether the prevalence of myopia will be higher for more recent birth cohorts PURPOSE This study estimates the prevalence of common visual disorders ( amblyopia , strabismus , refractive errors ) in a group of inner-city school children . In addition , the study addresses the issue of access to care for vision-screening programs , specifically for children with recognized difficulties in obtaining routine medical care . METHODS School children from an inner-city elementary school were enrolled into a prospect i ve vision-screening program combining the identification arm ( screening ) and diagnostic/treatment arm ( ophthalmic examination ) . The screening consisted of Snellen E optotypes presented at a 10-foot test distance . Each child failing the vision screening was examined by an ophthalmologist at the school using st and ard protocol . This allowed the authors to examine all children identified through the vision-screening program . RESULTS Six-hundred eighty children were screened during the 1993 to 1994 school year . Eleven percent ( 76 ) failed the vision screening and were examined , 68 of whom failed the ophthalmic examination . The estimated prevalence of visual morbidity was as follows : amblyopia , 3.9 % ; st 
    Output:
    
AUTHORS ' CONCLUSIONS Vision screening plus provision of free spectacles improves the number of children who have and wear the spectacles they need compared with providing a prescription only .
This may lead to better educational outcomes .
Health education interventions , as currently devised and tested , do not appear to improve spectacle wearing in children .
In lower-income setting s , ready-made spectacles may provide a useful alternative to expensive custom-made spectacles