Figure 3. The best fit of the consumption–diffusion model (see) to P_O2 profiles measured in 5% external oxygen.

The data were well fitted by the two-compartment model using Sigma Plot 2000 (SPSS Inc., Chicago, IL, USA). At 5% external oxygen, derived values for the length constants for oxygen consumption in the outer (mitochondria-rich) and central (mitochondria-free) regions of the lens were about 1 mm, which implies that the rates of oxygen consumption in these two domains are nearly the same. Based on measurements of total lens oxygen consumption (Q̇_O2) in 5% external oxygen and the best fit values of length constants, we estimate that the effective diffusion coefficient for oxygen in the lens is 3 × 10⁻⁵ cm² s⁻¹ and the time constant for oxygen consumption within any lens cell is about 5 min. Note that 5% oxygen in the bath corresponds to a partial pressure of 36 mmHg.