Oxygen consumption of the rabbit cornea

PURPOSE Tear oxygen tension beneath contact lenses, measured in a previous study, was found to be lower than mathematical model predictions. In this study, the authors developed a phosphorescence-based technique for measuring corneal O-2 consumption (Q(O2)) to determine whether errors in previous determinations of Q(O2) could explain the discrepancy between measured and predicted tear oxygen tension. METHODS. Corneal oxygen consumption is measured using the phosphorescence quenching of Pd-meso-tetra(4-carboxyphenyl)porphine by oxygen. Oxygen tension of a pH 7.5 Ringer's solution is measured in an airtight chamber that holds an excised rabbit cornea, and Q(O2) is calculated from the decreased P-O2 in the stirred chamber solution. Q(O2) rates are measured for the whole trephined rabbit cornea with the epithelium, the endothelium, or both, removed, which makes possible the estimation of the consumption rates of the epithelium, stroma, and endothelium. RESULTS. Control experiments indicated that the cornea Q(O2) was constant for 3 hours and that exposure to 2,4-dinitrophenol increased Q(O2). Mean Q(O2) rates (microliters of O-2/cm(2) per hour) were: whole cornea. Q(O2) = 7.53, epithelium, Q(O2) = 3.73; stroma, Q(O2) = 2.97; and endothelium, Q(O2) = 0.86. CONCLUSIONS. Phosphorescence-based measurements can be used to determine the Q(O2) of the component layers of the cornea. Estimates of Q(O2) in this study were similar to previous measurements, indicating that the discrepancy of tear Po, measures and model predictions are not a result of errors in the Q(O2) measurements at pH 7.5.