title: Oxygen diffusion and edema with modern scleral rigid gas permeable contact lenses.
abstract: OBJECTIVE
  We defined the theoretical oxygen tension behind modern scleral contact lenses (CLs) made of different rigid gas permeable (RGP) materials, assuming different thickness of the tear layer behind the lens. A second goal was to show clinically the effect of the postlens tear film on corneal swelling.
  
  
  METHODS
  We simulated the partial pressure of oxygen across the cornea behind scleral CLs made of different lens materials (oxygen permeability Dk, 75-200 barrer) and different thickness (Tav, 100-300 μm). Postlens tear film thicknesses (Tpost-tear) ranging from 150 to 350 μm were considered. Eight healthy subjects were fitted randomly with a scleral lens with a thin and a thick postlens tear layer in two different sessions for a period of 3 hours under open-eye conditions.
  
  
  RESULTS
  The CLs with less than 125 barrer of Dk and a thickness over 200 μm depleted the oxygen availability at the lens-cornea interface below 55 mm Hg for a postlens tear film of 150 μm. For a postlens tear film thickness of 350 μm, no combination of material or lens thickness will meet the criteria of 55 mm Hg. Our clinical measures of corneal edema showed that this was significantly higher (P < 0.001, Wilcoxon signed ranks test) with the thicker compared to the thinner Tpost-tear (mean ± SD, 1.66 ± 1.12 vs. 4.27 ± 1.19%).
  
  
  CONCLUSIONS
  Scleral RGP CLs must be comprised of at least 125 barrer of oxygen permeability and up to 200 μm thick to avoid hypoxic effects even under open eye conditions. Postlens tear film layer should be below 150 μm to avoid clinically significant edema.
authors.affiliation: Departamento de Termodinámica Aplicada, ETSII, Universidad Politécnica de Valencia, Valencia, Spain.
authors.forename: Vicente
authors.initials: V
authors.lastname: Compañ
authors.affiliation: Clinical & Experimental Optometry Research Lab (CEORLab), Center of Physics (Optometry), School of Sciences, University of Minho, Braga, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Oliveira
authors.affiliation: Departamento de Física, Universitat Jaume I, Castellón, Spain.
authors.forename: Marcel
authors.initials: M
authors.lastname: Aguilella-Arzo
authors.affiliation: Departamento de Termodinámica Aplicada, ETSII, Universidad Politécnica de Valencia, Valencia, Spain.
authors.forename: Sergio
authors.initials: S
authors.lastname: Mollá
authors.affiliation: Clinical & Experimental Optometry Research Lab (CEORLab), Center of Physics (Optometry), School of Sciences, University of Minho, Braga, Portugal.
authors.forename: Sofia C
authors.initials: SC
authors.lastname: Peixoto-de-Matos
authors.affiliation: Clinical & Experimental Optometry Research Lab (CEORLab), Center of Physics (Optometry), School of Sciences, University of Minho, Braga, Portugal.
authors.forename: José M
authors.initials: JM
authors.lastname: González-Méijome
mesh_terms: D003263:Contact Lenses, Hydrophilic / Q000009:adverse effects*; D015715:Corneal Edema / Q000209:etiology / Q000378:metabolism*; D004058:Diffusion; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D010539:Permeability; D012030:Refractive Errors / Q000378:metabolism / Q000628:therapy; D012590:Sclera / Q000378:metabolism*; D013666:Tears / Q000737:chemistry; D055815:Young Adult
chemical_list: D010100:Oxygen
keywords: boundary layers; corneal edema; oxygen transmissibility; scleral lenses; tear film