title: Long-term effect of orthokeratology on the anterior segment length.
abstract: OBJECTIVE
  To compare the effects of normal growth and longer term use of orthokeratology (ortho-k) on ocular biometric parameters in the anterior segment, including central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (CLT), and anterior segment length (ASL).
  
  
  METHODS
  Baseline and six monthly data were retrieved from 78 subjects (aged 7-10 years, with myopia≤4.00D and astigmatism≤1.25D) who had completed a two-year randomized clinical trial using ortho-k for myopia control. They were randomly assigned to wear ortho-k lenses or single-vision spectacles (control). Anterior segment parameters were measured with the Pentacam after cycloplegia.
  
  
  RESULTS
  No significant changes in CLT and ASL over time were observed in either group of subjects (37 ortho-k; 38 control). In the control group, CCT remained unchanged during the study period but in the ortho-k group, it was significantly reduced by an average of 0.009mm by the 6-month visit (p<0.001) and remained unchanged thereafter. No significant changes in ACD was found in the ortho-k group but it was significantly increased by an average of 0.04mm (p=0.001) in the control group.
  
  
  CONCLUSIONS
  CLT nor ASL did not change over time in either control or ortho-k subjects. Although ACD significantly increased in the control subjects and CCT significantly reduced in the first six months of ortho-k lens wear, these changes were small and did not affect the overall ASL.
authors.affiliation: School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China. Electronic address: orpeggy@gmail.com.
authors.forename: Sin-Wan
authors.initials: SW
authors.lastname: Cheung
authors.affiliation: School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China.
authors.forename: Pauline
authors.initials: P
authors.lastname: Cho
mesh_terms: D000375:Aging / Q000473:pathology*; D000869:Anterior Eye Segment / Q000473:pathology*; D002648:Child; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009216:Myopia / Q000473:pathology* / Q000628:therapy*; D054158:Orthokeratologic Procedures / Q000295:instrumentation / Q000379:methods*; D016896:Treatment Outcome
keywords: Anterior chamber depth; Anterior segment length; Myopia control; Orthokeratology