title: Factors influencing the measurement of oxygen shortfall of the human cornea: sequencing of test conditions.
abstract: OBJECTIVE
  The effects of sequencing of test conditions, in this case contact lens thicknesses, on the measurement of the oxygen shortfall of human corneas were studied.
  
  
  METHODS
  Corneal oxygen uptake rates were measured with a Clark-type polarographic electrode on the central, unanesthetized right corneas of 14 human subjects. Measurements were made under the following conditions: (1) the normal open eye; (2) after 5 min of static (without blinking) wear of each of seven rigid gas permeable lenses of seven center thicknesses (0.18, 0.12, 0.16, 0.20, 0.24, 0.28, and 0.32 mm); (3) after 5 min of static wear of a polymethylmethacrylate (PMMA) contact lens. Lens thicknesses were randomly assigned numbers, which were sequenced in seven cycles. Two subjects were assigned to each sequencing cycle, and each subject participated in two identical sessions.
  
  
  RESULTS
  The interaction of order x thickness was determined to be insignificant (F=0.99; p=0.5101). The effect of lens order was also insignificant (F=0.76; p=0.6239), indicating that the order of lens placement did not affect the measured corneal oxygen shortfall. Not surprisingly, the analysis indicated a significant effect of lens thickness on corneal oxygen shortfall (F=3.94; p=0.0032).
  
  
  CONCLUSIONS
  The sequencing of lenses of various thicknesses on the cornea does not affect the measurement of corneal oxygen shortfall.
authors.affiliation: The Ohio State University, College of Optometry, 338 West Tenth Avenue, Columbus, 43210-1240 OH, USA.
authors.forename: Jane M
authors.initials: JM
authors.lastname: Chi
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Fink
authors.forename: Richard M
authors.initials: RM
authors.lastname: Hill
authors.forename: G Lynn
authors.initials: GL
authors.lastname: Mitchell
mesh_terms: D000328:Adult; D003261:Contact Lenses; D003315:Cornea / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010539:Permeability; D019904:Polymethyl Methacrylate / Q000737:chemistry*
chemical_list: D019904:Polymethyl Methacrylate; D010100:Oxygen