Analysis of the application of the generalized monod kinetics model to describe the human corneal oxygen-consumption rate during soft contact lens wear
This work is an analysis of the application of the
generalized Monod kinetics model describing human corneal
oxygen consumption during soft contact lens wear to models
previously used by Chhabra et al. (J Biomed Mater Res B
Appl 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 vivo
estimations provided by Bonanno [Bonanno et al., Invest
Ophthalmol Vis Sci 2002;43:371-376, and Bonanno et al
2009]. We consider four hydrogel and six silicone hydrogel
lenses. The cornea is considered a single homogeneous layer,
with constant oxygen permeability regardless of the type
of lens worn. Our calculations yield different values for the
maximum oxygen consumption rate Qc,max, whith differents
oxygen tensions (high and low pc) at the cornea-tears interface.
Surprisingly, for both models, we observe an increase
in oxygen consumption near an oxygen tension of 105
mmHg until a maximum is reached, then decreasing for
higher levels of oxygen pressure. That is, when lowering the
pressure of oxygen, the parameter Qc,max initially increases
depending 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, this
parameter decreases, possibly due to changes in the concentration
of glucose related to the anaerobic respiration. The
averaged in vivo human corneal oxygen consumption rate of
1.47 3 1024 cm3 of O2/cm3 tissue s, with Monod kinetics
model, considering all the lenses studied, is smaller than the
average oxygen consumption rate value obtained using the
Larrea and Buchler model. The impact that these calculations €
have on the oxygen partial pressure available at different
depths in the corneal tissue is presented and discussed, taking
into consideration previous models used in this studySIH is grateful to projects CONACYT SEP-2004-C01-47070,
UNAM-DGAPA-PAPIIT IN113415, DGTIC-UNAM SC16-1-IR-
113, to the Red Tematica de la Materia Condensada BlandaCONACYT
for a postdoctoral fellowship, and to CONACYT for a
retention fellowship No. 207109. We thank Dr. Barry A. Weissman
from the Southern California College of Optometry at Marshall
B Ketchum University, Fullerton CA, USA for helpful
comments and discussion
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