title: A review of the Holden-Mertz criteria for critical oxygen transmission.
abstract: OBJECTIVE
  Holden and Mertz established the foundations for the new generation of silicone hydrogel contact lenses for daily and extended wear in 1984. Absence of lens-induced corneal swelling was their premise and although this was possible with daily wear, the goal with extended wear seemed almost impossible because of the limitation of hydrogel materials. Experience with extended and daily wear of disposable contact lenses during the last 2 decades and, more recently, with silicone hydrogels has led to the reconsideration of the validity of the findings of Holden and Mertz.
  
  
  RESULTS
  A pivotal influence on the Holden and Mertz critical Dk/t value for closed-eye lens wear was exerted by two numbers: the no-lens wear corneal edema level (4%) and the silicone lens data point (Dk/t of 182x10, closed-eye edema level of 2.6%). Subsequent publications appear to give a more accurate assessment of the no-lens closed-eye corneal edema level, and there are also more recent measurements of silicone hydrogel lens Dk/t and corneal edema responses.
  
  
  CONCLUSIONS
  It now appears that the Holden and Mertz criteria for extended-wear critical Dk/t should be revised upwards to at least 125x10.
authors.forename: Desmond
authors.initials: D
authors.lastname: Fonn
authors.forename: Adrian S
authors.initials: AS
authors.lastname: Bruce
mesh_terms: D003262:Contact Lenses, Extended-Wear; D003315:Cornea / Q000502:physiology*; D015715:Corneal Edema / Q000209:etiology / Q000517:prevention & control; D004867:Equipment Design; D006801:Humans; D010100:Oxygen / Q000378:metabolism*; D010539:Permeability; D012826:Silicone Elastomers
chemical_list: D012826:Silicone Elastomers; D010100:Oxygen