The “L” in Dk/L

We measured the Dk (oxygen permeability) of one specific hydrogel contact lens material (phemfilcon A, nominally 38% water content and ionic) by use of the conventional single chamber polarographic technique at 35°C. When corrected for the boundary and edge effect, Dk was found to be 13 x 10 −11 cm 2 ml O 2 /s ml mm Hg. (These units will be used for this term throughout the remainder of this report.) We also used the polarographic cathode as a model cornea to measure the Dk/L (oxygen transmissibility) of 7 powered contact lenses (−5 to +15 D) made from the same material by the same manufacturer. We found values ranging from 5 to 15 x 10 −9 cm ml O 2 /s ml mm Hg. (These units will also be used for this term throughout this report.) From analysis of these data, we found that any reasonable model (of the several previously proposed) for L could be used to predict the polarographically measured oxygen transmissibility of the low minus (−5 to ‐ 1 D) powered contact lenses, but that plus powered lenses, at least on this measurement apparatus, give Dk/L values that are closer to predictions based on the observed Dk and central thickness rather than any version of average thickness.