Oxygen Tension Measurements

The equivalent oxygen percentage (EOP) technique of Hill and the technique of Rasson and Fatt are two commonly used methods to quantify the oxygen tension underneath a contact lens for the open‐eyelid case. This study compares these two techniques. Five subjects and six contact lenses of various center thicknesses and oxygen transmissibilities were used. Each subject wore each lens for which the oxygen tension was measured by these two methods. For lenses of approximately 0.23 mm center thickness, the two methods gave similar oxygen values. For contact lenses significantly thicker or thinner, the two methods gave very different oxygen values. However, these oxygen values were related in a specific manner; a strong linear relation was found for contact lens center thickness vs. the ratio of the two oxygen values found by the two methods.