title: [The cross-sectional study of dynamic refractive status in Xi'an middle school students].
abstract: OBJECTIVE
  To obtain the basic data of refractive status, especially the myopia prevalence rate in Xi'an middle school students.
  
  
  METHODS
  The cross-sectional study was conducted in two Xi'an city middle schools. The object ophthlmic examinations such as non-cycloplegic objective refraction, visual acuity, oculr pressure and fundus evaluation were taken on all students by special trained ophthalmologists and nurses. The special designed inventory scale was filled in and input in a special computer program. Then the data were statistically analyzed with SPSS11.0.
  
  
  RESULTS
  (1) In the 3711 middle school students (average age of 13-18 years), the prevalence rate of myopia was 91.2%, including 51.7% low myopia, 31.8% moderate myopia, 7.7% high myopia, 5.7% emmetropia and 3.1% hypermetropia. Among 6 grades, the constituents of moderate and high myopia groups were significantly increased with the age growing. (2) The average diopter of spherical equivalent refraction was (-2.76 +/- 2.24)D, that of low myopia was (-1.68 +/- 0.76)D, moderate myopia (-4.35 +/- 0.84)D and high myopia (-7.47 +/- 1.33)D. In the junior 1st grade the average diopter of spherical equivalent refraction was (-1.57 +/- 1.66)D, the junior 2nd, (-1.94 +/- 2.04)D,the junior 3rd, (-3.26 +/- 2.09)D, the senior 1st grade' (-3.29 +/- 2.49)D, the senior 2nd, (-3.09 +/- 2.31)D and the senior 3nd, (-3.57 +/- 2.25) D. There were significant differences (P=0.000) in the average diopter of spherical equivalent refraction in all the 6 grades. However, there was no significant difference among the junior 3rd, senior 1st and senior 2nd grade. (3) The degree of myopia in female students [(-2.88 +/- 2.25)D] and the right eyes [(-2.86 +/- 2.19)]D was significantly higher than that in male students [(-2.65 +/- 2.23)D] (P = 0.000) and the left eyes [(-2.67 +/- 2.29)D] (P = 0.009) respectively.
  
  
  CONCLUSIONS
  The constituesnts of myopia were definitely changed in and above the junior 3rd grade; meanwhile the progression of myopia in female students and the right eyes is earlier than that in male students and the left eyes'. The result indicates that interventions of myopia progression performed at the stage may retard the myopia progression and reduce the prevalence of myopia.
authors.affiliation: Department of Ophthalmology, Xi'an Central Hospital, Xi'an 710003, China.
authors.forename: Yining
authors.initials: Y
authors.lastname: Shi
authors.forename: Ping
authors.initials: P
authors.lastname: He
authors.forename: Hongying
authors.initials: H
authors.lastname: Zhao
authors.forename: Wenjing
authors.initials: W
authors.lastname: Cao
mesh_terms: D000293:Adolescent; D000328:Adult; D002681:China / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000453:epidemiology; D008297:Male; D009216:Myopia / Q000453:epidemiology*; D012029:Refraction, Ocular; D012307:Risk Factors