Analysis of the application of the generalized monod kinetics model to describe the human corneal oxygen-consumption rate during soft contact lens wear

摘要

This work is an analysis of the application of thegeneralized Monod kinetics model describing human cornealoxygen consumption during soft contact lens wear to modelspreviously used by Chhabra et al. (J Biomed Mater Res BAppl Biomater, 2009a;90:202-209, Optom Vis Sci 2009b;86:454-466) and Larrea and Buchler (Invest Ophthalmol Vis €Sci 2009;50:1076-1080). We use oxygen tension from in vivoestimations provided by Bonanno [Bonanno et al., InvestOphthalmol Vis Sci 2002;43:371-376, and Bonanno et al2009]. We consider four hydrogel and six silicone hydrogellenses. The cornea is considered a single homogeneous layer,with constant oxygen permeability regardless of the typeof lens worn. Our calculations yield different values for themaximum oxygen consumption rate Qc,max, whith differentsoxygen tensions (high and low pc) at the cornea-tears interface.Surprisingly, for both models, we observe an increasein oxygen consumption near an oxygen tension of 105mmHg until a maximum is reached, then decreasing forhigher levels of oxygen pressure. That is, when lowering thepressure of oxygen, the parameter Qc,max initially increasesdepending on the intensity of the change in pressure. Which,it could be related with the variation of the pH. Furthermore,it is also noted that to greater reductions in pressure, thisparameter decreases, possibly due to changes in the concentrationof glucose related to the anaerobic respiration. Theaveraged in vivo human corneal oxygen consumption rate of1.47 3 1024 cm3 of O2/cm3 tissue s, with Monod kineticsmodel, considering all the lenses studied, is smaller than theaverage oxygen consumption rate value obtained using theLarrea and Buchler model. The impact that these calculations €have on the oxygen partial pressure available at differentdepths in the corneal tissue is presented and discussed, takinginto consideration previous models used in this study