title: Lens Dk/t influences the clinical response in overnight orthokeratology.
abstract: OBJECTIVE
  To investigate the influence of lens oxygen transmissibility (Dk/t) on the clinical response to overnight (ON) orthokeratology (OK) lens wear over 2 weeks.
  
  
  METHODS
  Eleven subjects (age, 20 to 39 years) were fitted with OK lenses (BE; Capricornia Contact Lens) in both eyes. Lenses in matched design/fitting but different materials (Boston EO and XO; nominal Dk/t: 26 and 46 ISO Fatt, respectively) were worn ON only in the two eyes over a 2-week period. Changes in logarithm of the minimum angle of resolution visual acuity, subjective refraction (spherical equivalent), corneal apical radius ro and asphericity Q (Medmont E300), and central stromal thickness (Holden-Payor optical pachometer) were measured.
  
  
  RESULTS
  There were statistically significant differences in outcomes between the two lens materials (analysis of variance, p < 0.001) throughout the study. After 2 weeks of ON OK lens wear, changes from baseline (mean ± standard deviation) with the EO lenses were significantly less than XO for visual acuity (-0.72 ± 0.37 vs. -0.83 ± 0.41; p = 0.012), refraction [+2.19 ± 0.73 diopter (D) vs. +2.74 ± 0.70 D; p = 0.004], ro (0.34 ± 0.08 mm vs. 0.46 ± 0.11 mm; p < 0.001), and Q (0.26 ± 0.08 vs. 0.36 ± 0.08; p < 0.001). After the first ON OK lens wear, change in central stromal thickness was greater for EO compared with XO (27 ± 36 μm vs. 10 ± 31 μm; p = 0.05), but ON edema was reduced after 2 weeks for both lens materials (8 ± 25 μm vs. -1 ± 33 μm; p > 0.05).
  
  
  CONCLUSIONS
  An increase in lens Dk/t appears to increase the clinical effects of ON reverse-geometry lens wear over the medium term. This adds further support to the recommendation that high Dk materials should be used for ON OK not only to provide physiological advantages but also to optimize clinical outcomes.
authors.affiliation: School of Optometry and Vision Science, University of New South Wales,Sydney, New South Wales, Australia.
authors.forename: Edward
authors.initials: E
authors.lastname: Lum
authors.forename: Helen A
authors.initials: HA
authors.lastname: Swarbrick
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D002940:Circadian Rhythm; D003261:Contact Lenses; D015715:Corneal Edema / Q000473:pathology; D003319:Corneal Stroma / Q000473:pathology; D004867:Equipment Design; D006801:Humans; D054158:Orthokeratologic Procedures / Q000295:instrumentation*; D010100:Oxygen / Q000493:pharmacokinetics*; D012029:Refraction, Ocular; D013997:Time Factors; D014792:Visual Acuity; D055815:Young Adult
chemical_list: D010100:Oxygen