title: Long-term changes in corneal morphology induced by overnight orthokeratology.
abstract: OBJECTIVE
  To assess long-term morphological and biometric corneal changes produced by overnight orthokeratology and to examine their recovery after cessation of contact lens wear.
  
  
  METHODS
  Prospective, single-center, longitudinal trial. Fifteen right eyes with low to moderate myopia underwent overnight orthokeratology for 1 year. The central cornea was examined using a confocal microscope and changes determined in visual acuity, refractive error and corneal topography. Cell counts were performed using both the confocal microscope's software and the image analysis software of the USA Health Institute. All measurements were made during orthokeratology treatment and 1 month after discontinuing treatment.
  
  
  RESULTS
  No significant changes in endothelial cell density were observed over time but polymegethism increased significantly and baseline values were not recovered (p < 0.01). Stromal cell density remained unchanged though numbers of activated keratocytes increased during the study and returned to baseline when lens wear ceased. Basal epithelium cell densities significantly fell (p < 0.01) and epithelial wing and superficial cells showed enhanced visibility (p < 0.05). Superficial cells increased in height and width; this width increase being significant after 1 year of orthokeratology (p < 0.01). All epithelial cell changes returned to baseline. Corneal thickness, Bowman layer thickness, subbasal plexus thickness and epithelial thickness were reduced in the central cornea but the stroma was thickened. Of these changes, the decrease in epithelium thickness reached statistical significance (p < 0.01) and baseline values were not recovered.
  
  
  CONCLUSIONS
  Overnight orthokeratology induces structural and optical changes particularly in the central corneal epithelium during myopia treatment. If confirmed, the irreversible changes detected indicate a need for further investigation.
authors.affiliation: Department of Optics II, University School of Optics, C/Arcos de Jalón s/n, Madrid, Spain. amnop@fis.ucm.es
authors.forename: Amelia
authors.initials: A
authors.lastname: Nieto-Bona
authors.forename: Ana
authors.initials: A
authors.lastname: González-Mesa
authors.forename: M Paz
authors.initials: MP
authors.lastname: Nieto-Bona
authors.forename: César
authors.initials: C
authors.lastname: Villa-Collar
authors.forename: Amalia
authors.initials: A
authors.lastname: Lorente-Velázquez
mesh_terms: D000293:Adolescent; D000328:Adult; D002452:Cell Count; D003315:Cornea / Q000473:pathology*; D060527:Corneal Keratocytes / Q000473:pathology; D019781:Corneal Topography; D004728:Endothelium, Corneal / Q000473:pathology; D019573:Epithelium, Corneal / Q000473:pathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D018613:Microscopy, Confocal; D009216:Myopia / Q000503:physiopathology / Q000628:therapy*; D054158:Orthokeratologic Procedures; D011446:Prospective Studies; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult