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Background Myopia is one of the correctable visual impairments in the developed world that affects mostly to adults and children.We examined the effect of lower degree convex lenses to determine whether it could result in efficacy in preventing the myopia onset among 612 school children aged 6-12 years in Beijing,China Methods A stratified cluster sampling,the school-based trial was conducted in Beijing,China,from November 2010 to June 2011(Half year).204 students from grade 1 to 5 wore 100-degree convex lenses for 1-2 hours while they were writing their homework at home under the supervision of their parents every day.Consistently 527 students were randomly selected to the control group.We compared the incidence of myopia and changes of right eye spherical equivalent between these two groups after half-year follow-up to evaluate the efficacy of the myopia prevention method.Results There was a significant(P=0.0188)difference between the incidences of myopia in the intervention group (12.2%)and control group(19.9%).The changes of spherical equivalent of the intervention group was less than that in the control group(P=0.0387)compared to the baseline at a half year period.This school based trial revealed that wearing convex spectacles can reduce 57.9%risk(OR=0.421,95%CI=0.232~0.763,p=0.0044)of myopia in school students in the trial Conclusion Wearing 100 degree convex spectacles can reduce the development of myopia(spherical refractive error change)in children over the half-year period.To evaluate the long-term effect of the interventions,further research is needed.