The reliability of polarographic oxygen measurements across gas permeable contact lenses

A polarographic method of oxygen determination across contact lenses has been developed. A custom designed polarographic cell, with a platinum cathode and a silver anode was used to measure a series of specially prepared contact lens samples made from four gas permeable contact lens materials currently commercially available. On a series of measurements the polarographic current was shown to be highly repeatable without the need for a wet membrane between the lens and the cathode. A layer of solution was adequate. The greatest variability was found with the thinnest sample of the highest oxygen permeable material. The results were plotted using the resistance (L/Dk) of the readings against sample thickness. Three of the four examples showed a curvilinear function and the other a linear relationship relative to sample thickness. From these graphs the reciprocal of the slope of the curve at zero thickness gave the measured oxygen permeability of the material. The significance of this system towards setting up a standard for the measurement of oxygen permeability of contact lens materials is discussed.