Figure 1. The relationship between internal and external P_O2 in the isolated bovine lens.

A, the optode tip was inserted into the lens core and the response of core P_O2 to a change in the oxygen concentration of the bathing medium (from 1 to 21%) was monitored. Note that a new steady-state value was established within 4 h. B, intralenticular P_O2 profiles were recorded from a single lens along the polar (•) or equatorial axis (○). Measurements were made in tissue equilibrated with 5% external oxygen. The profiles are symmetric and exhibit steep cortical P_O2 gradients and a central region of low (1–2 mmHg) P_O2. C, internal P_O2 profiles were measured in bovine lenses equilibrated with 1% (•), 5% (□), or 21% oxygen (▪). In each case, data represent the mean ±s.d. of at least six independent measurements. Note that the upper measurement limit for the optode system is 100 mmHg. This value is exceeded in the peripheral cell layers of lenses incubated in 21% oxygen. The slope of the P_O2 profile in the outer 2–3 mm of tissue is artificially reduced as a consequence. D, the relationship between internal P_O2(measured in the centre of the lens) and external P_O2 was determined in isolated bovine lenses. Note that the P_O2 in the centre of the lens does not increase until external P_O2 is raised to supraphysiological values (≥ 70 mmHg). Data represent at least six independent measurements at each oxygen concentration.