title: Oxygen tension beneath piggyback contact lenses and clinical outcomes of users.
abstract: OBJECTIVE
  Patients with keratoconus sometimes wear a rigid contact lens as a piggyback over a countersunk soft one. This geometry restricts movement of the rigid lens over the central cornea and may also reduce corneal oxygenation. This aim of this study was to estimate the equivalent oxygen percentage beneath such lenses and to review the clinical records of users to determine their success rate.
  
  
  METHODS
  The right eyes of four normal subjects were covered for 5 minutes with a combination of rigid gas permeable (Boston ES or 7 [Polymer Technology Corp., Rochester, NY]) and soft (Acuvue [Johnson & Johnson, Jacksonville, FL], Keraflex [KF] 3 or 5 [Blanchard, Sherbrooke, QC, Canada]) contact lenses. After removal of the lenses, oxygen tension was measured with a Clark electrode. In order to determine whether measurements of oxygen tension were supported by clinical data, the clinical files of 11 patients fitted with KF 5-Boston ES piggyback lenses were reviewed for the presence of corneal edema.
  
  
  RESULTS
  Mean relative equivalent oxygen percentage ranged from 6.9% to 11.2% beneath the following lens combinations: KF 3-Boston ES; KF 3-Boston 7; KF 5-Boston ES; KF 5-Boston 7; Acuvue-Boston ES; and Acuvue-Boston 7. Of the ten patients followed after dispensing, none had any sign of corneal edema. Nine had worn their contact lenses for periods up to 6 years.
  
  
  CONCLUSIONS
  Based on the measured equivalent oxygen percentage and on the absence of corneal edema in patients, the combination of countersunk KF 5 with Boston ES lenses provides enough oxygen to fulfill corneal needs in oxygen during daily wear.
authors.affiliation: School of Optometry, Université de Montréal, QC, Canada.
authors.forename: C J
authors.initials: CJ
authors.lastname: Giasson
authors.forename: N
authors.initials: N
authors.lastname: Perreault
authors.forename: D
authors.initials: D
authors.lastname: Brazeau
mesh_terms: D000293:Adolescent; D000328:Adult; D003261:Contact Lenses; D003263:Contact Lenses, Hydrophilic; D003315:Cornea / Q000378:metabolism*; D015715:Corneal Edema / Q000517:prevention & control; D005260:Female; D006801:Humans; D017736:Ion-Selective Electrodes; D007640:Keratoconus / Q000378:metabolism* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism*; D010539:Permeability
chemical_list: D010100:Oxygen