title: Differences between overnight and long-term wear of orthokeratology contact lenses in corneal contour, thickness, and cell density.
abstract: OBJECTIVE
  To investigate changes in corneal topography and morphology in human eyes wearing orthokeratology (OK) lenses for overnight and over a 5-year period.
  
  
  METHODS
  Fifty-six adults with moderate myopia were assigned to 2 groups based on age matching: 5-year lens wear (n = 26, 51 eyes) and 1-night lens wear (n = 30, 60 eyes). All subjects wore reverse-geometry OK lenses with the eyes before 1-night lens wear serving as a control to both the groups. Visual acuity, slit-lamp biomicroscopy, confocal microscopy, and corneal topography were assessed before and after lens wear.
  
  
  RESULTS
  Visual acuity was improved satisfactorily with flattening of the central cornea in both lens wear groups. Corneal thickness increased extensively in the 1-night lens wear group but only paracentrally in the 5-year lens wear group. Central epithelial thinning with a decreased density of the basal cells was only observed in the 5-year group. Keratocyte density was reduced throughout the entire corneal thickness for the 2 groups. Endothelium was normal in density and morphology for the 2 groups.
  
  
  CONCLUSIONS
  Short-term and long-term OK lens wear can effectively correct myopia by flattening the cornea. The flattened cornea in the short-term lens wear is mainly because of the thickening of the midperipheral cornea. In the long-term lens wear, however, this change is associated with thickening of the midperipheral cornea and thinning of the central corneal epithelium.
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China.
authors.forename: Xingwu
authors.initials: X
authors.lastname: Zhong
authors.forename: Xiaolian
authors.initials: X
authors.lastname: Chen
authors.forename: Ruo Zhong
authors.initials: RZ
authors.lastname: Xie
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
authors.forename: Saiqun
authors.initials: S
authors.lastname: Li
authors.forename: Xiao
authors.initials: X
authors.lastname: Yang
authors.forename: Xiangming
authors.initials: X
authors.lastname: Gong
mesh_terms: D000328:Adult; D002452:Cell Count; D003261:Contact Lenses / Q000706:statistics & numerical data*; D003262:Contact Lenses, Extended-Wear / Q000706:statistics & numerical data*; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography; D005260:Female; D006801:Humans; D008297:Male; D033401:Microscopy, Acoustic; D018613:Microscopy, Confocal; D009216:Myopia / Q000628:therapy*; D054158:Orthokeratologic Procedures; D013997:Time Factors; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult