[Survey on the refractive state among primary and middle school students in Tsinan].
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002681:China; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000453:epidemiology; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000453:epidemiology; D014785:Vision, Ocular