May 2004
Volume 45, Issue 13
ARVO Annual Meeting Abstract  |   May 2004
Deficiencies in the Dk/t paradigm for describing corneal oxygenation during contact lens wear
Author Affiliations & Notes
  • N.A. Brennan
    Brennan Consultants, Melbourne, Australia
  • Footnotes
    Commercial Relationships  N.A. Brennan, Johnson & Johnson F; Bausch & Lomb F, C.
  • Footnotes
    Support  none
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 1550. doi:
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      N.A. Brennan; Deficiencies in the Dk/t paradigm for describing corneal oxygenation during contact lens wear . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1550.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract: : Purpose: To evaluate the Dk/t paradigm for describing corneal oxygenation during contact lens wear by comparison to an 8–layer oxygen diffusion model in which the minimum Dk/t to avoid corneal anoxia during contact lens wear, comparative consumption with different contact lens types, and the interaction of different corneal consumption parameters on such estimates are modelled. Methods: Profiles were constructed for representative human corneal models incorporating different oxygen demands and layer thicknesses. Standard consumption rates and Dk values for individual corneal layers were based on the model of Harvitt and Bonanno (Optom Vis Sci 1999). Thickness estimates of 3µm, 50µm, 480µm were used as standard values for post–lens tear film, epithelial and stromal thickness, respectively. Consumption was set to zero when pO2 fell to zero within a given layer, and the boundaries of these sub–layers were determined by iteration. Variations in thickness and consumption rates were based on coefficient of variation estimates from the literature. Results: Minimum oxygen criteria ranging from Dk/t values of 7 to 52 x 10â|*128*|"9(cm/sec)(ml02/ml.mmHg) for the open eye and 21 to infinity for the closed eye were derived dependent upon whether the calculation used the thin or thick cornea model, correction for acidotic change in consumption and a criterion of avoiding epithelial or stromal anoxia. Above a Dk/t of 100 x 10â|*128*|"9(cm/sec)(ml02/ml.mmHg), total consumption was relatively steady rising by less than 10% with a Dk/t of infinity, even with consumption rates several times the standard. Conclusions: Minimum Dk/t criteria are highly sensitive to layer consumption and thickness variation in the diffusion models, despite modest change in steady state oxygen profiles. Furthermore, relative total consumption values are relatively insensitive to contact lens Dk/t changes above approximately 100. It is apparent that the Dk/t parameter has limited value in describing corneal oxygenation and I recommend that a model based on the percentage of normal total corneal consumption be pursued.

Keywords: contact lens • cornea: clinical science • cornea: epithelium 

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