title: The control effect of orthokeratology on axial length elongation in Chinese children with myopia.
abstract: BACKGROUND
  To retrospectively compare axial elongation in children with different degrees of myopia wearing spectacles and undergoing ortho-k treatment.
  
  
  METHODS
  The medical records of 128 patients who were fitted with spectacles or orthokeratology (ortho-k) lenses in our clinic between 2008 and 2009 were reviewed. Ortho-k group comprised 65 subjects and 63 subjects wearing spectacles were included in the control group. Subjects were also divided into low-myopia, moderate-myopia and high-myopia groups, based on the basic spherical equivalent refractive error. Axial length periodically measured over 2-year of lens wear and changes in axial length were compared between treatment groups and between subgroups with different degrees of myopia.
  
  
  RESULTS
  The control group exhibited more changes in axial length than the ortho-k group at both 12 months (0.39 ± 0.21 mm vs 0.16 ± 0.17 mm, p <0.001) and 24 months (0.70 ± 0.35 mm vs 0.34 ± 0.29 mm, p <0.001). Axial length elongation was estimated to be slower by about 51% in the ortho-k group. Similar results were found for the subgroups (49%, 59% and 46% reductions, respectively). In the group with low and moderate myopia, the annual increases in axial length were significantly different between the ortho-k and control groups during both the first ( Low myopia: 0.19 ± 0.17 mm vs 0.40 ± 0.18 mm, p = 0.001; Moderate myopia: 0.14 ± 0.18 mm vs 0.45 ± 0.22 mm, p <0.001) and second ( Low myopia: 0.18 ± 0.14 mm vs 0.32 ± 0.19 mm, p = 0.012; Moderate myopia: 0.18 ± 0.16 mm vs 0.34 ± 0.30 mm, p = 0.030) years. In the high myopia groups, significant differences were only found between the ortho-k and control groups during the first year (0.16 ± 0.18 mm vs 0.34 ± 0.22 mm, p = 0.004). The 2-year axial elongation was significantly associated with initial age (p <0.001) and treatment (p <0.001), but not with gender, initial refractive error, initial axial length, initial corneal curvature.
  
  
  CONCLUSIONS
  This 2-year study indicates that ortho-k contact lens wear is effective for reducing myopia progression in children with low, moderate and high myopia.
authors.forename: Meng-Jun
authors.initials: MJ
authors.lastname: Zhu
authors.forename: Hao-Yan
authors.initials: HY
authors.lastname: Feng
authors.forename: Xian-Gui
authors.initials: XG
authors.lastname: He
authors.forename: Hai-Dong
authors.initials: HD
authors.lastname: Zou
authors.affiliation: Shanghai Eye Disease Prevention & Treatment Center, No, 380 Kangding Road, Jingan District, Shanghai 200040, China. jfzhu1974@hotmail.com.
authors.forename: Jian-Feng
authors.initials: JF
authors.lastname: Zhu
mesh_terms: D000293:Adolescent; D044466:Asian People / Q000208:ethnology; D058452:Axial Length, Eye / Q000503:physiopathology*; D002648:Child; D002681:China / Q000453:epidemiology; D005139:Eyeglasses; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000208:ethnology / Q000503:physiopathology / Q000628:therapy*; D054158:Orthokeratologic Procedures; D012189:Retrospective Studies