A model of oxygen flux through contact lenses

Abstract

Purpose: Although oxygen transmissibility has been a favored index to describe the physiologic performance of contact lenses, it has been maintained by some that the flux through a contact lens would be a more useful guide. Here, a model is described that allows contact lens oxygen flux to be estimated under open and closed eye wearing conditions.

Methods: The equivalent oxygen potential (EOP) was used to approximate the oxygen concentration beneath a contact lens. A logarithmic relation between corneal oxygen consumption and this oxygen level was substituted into Fick's Law to provide a mathematical model. Paired data of EOP and oxygen transmissibility (Dk/t), from a previous empiric derivation, were entered into a nonlinear regression analysis of this model.

Results: The modelling procedure produces a good fit to the selected data. The estimated maximum flux during open eye wear is 7.5 microL/cm2 x h, consistent with previous determinations. Error estimates increased from 0 to 0.55 microL/cm2/h at Dk/t values of 0 and 200 x 10(-9) Barrer/cm, respectively, for the open eye.

Conclusion: This study provides a workable model for estimating the oxygen flux through contact lenses. Varying the underlying relation between the oxygen tension beneath a lens and the oxygen flux produces minimal variation to the result. The model has a number of clinical applications, such as demonstrating the advantages of highly transmissible contact lenses and the limits to which increasing oxygen transmissibility can alter the corneal physiologic environment.