Spatial variation of the local tissue oxygen diffusion coefficient measured in situ in the cat retina and cornea

A method for measuring the local oxygen diffusion coefficient (D) in an intact tissue, in situ, in a living cat is described. Values of D were calculated from nonlinear regression analysis of the polarographic (turn-on) transients using a semi-empirical model for the retina and a theoretical one for the cornea. Two types of microelectrodes were employed: in the retina, ones with extremely short recesses; and in the cornea, bare metal needles. The local D in the cat retina was practically homogeneous with a mean of 1.97 +/- 0.11.10(-5) cm2/s, at its body temperature of 37-38 degrees C, 70.6 +/- 3.3 percent of that in isotonic saline at 37 degrees C. In the cat corneal stroma, at its normal temperature in situ of 33 degrees C, D was also virtually homogeneous with a mean of 1.19 +/- 0.20.10(-5) cm2/s, 42.8 +/- 7.3 percent of that in isotonic saline at 37 degrees C.