AIM: To investigate the prevalence of myopia among primary and middle school students aged 7 to 18 in Longkou City, Shandong Province, and to provide a scientific basis for prevention and control of myopia.

METHODS: The students aged 7 to 18 were enrolled through the method of stratified random and cluster sampling by the unit of schools and were investigated in Longkou, Shandong Province in 2015. A total of 58 schools were selected and 61 036 students were effectively sampled. All the subjects were divided into three-tiers based on geographical location: urban, rural-urban continuum, and rural areas. All the subjects were examined with the visual acuity and non-cycloplegic objective fraction. Microsoft Excel worksheet was used to establish a database, and SPSS 21.0 software was used for statistical analysis.

RESULTS: The prevalence of total myopia in the sample population of students of Longkou in 2015 was 49.81% from 7 to 18 years old. The overall prevalence of myopia increased fastest from 11 to 12 years old. And the prevalence of mild myopia of students aged 13 was highest. The prevalence of total myopia were 46.41% for boys and 53.39% for girls, which showed the prevalence of girls was higher than the boys'. The prevalence of myopia in urban, rural-urban continuum, and rural areas were 55.18%, 49.75%, 44.47%, respectively, and the prevalence of myopia in urban areas was the higher than the rural-urban continuum and the rural areas. The prevalence of total myopia gradually increased with age(r_s=0.943, P<0.05).

CONCLUSION: The results of the investigation showed a high prevalence of myopia among primary and middle school students in the city of Longkou, and gradually increased with age. The overall myopia prevalence for girls was higher than boys, and the prevalence was highest in urban areas.