Determination of the oxygen transmissibility and permeability of hydrogel contact lenses

To test the validity of the method of stacked hydrogel contact lenses to ob tain the oxygen permeability and transmissibility coefficients of the lense s, the coefficients of one low hydration (38% water) and two high hydration (55 and 58% water) hydrogel contact lenses stacked one to five on an oxyge n electrode were determined. From the oxygen diffusion through the lenses, the current intensity in the stationary state was determined, and from tl-l is the "instrument" the oxygen transmissibility was obtained. The permeabil ity coefficients of the lenses, corrected for edge effects, were obtained f rom the slope of the plot of the reciprocal of the transmissibility coeffic ients versus the lens thicknesses. The oxygen permeability and transmissibi lity coefficients of the lenses obtained neglected the boundary layers resi stance between the stacked lenses and, therefore, these are not the "true" coefficients. This article compares the "apparent" oxygen permeability coef ficients of the hydrogel contact lenses, obtained by others, with the "true " oxygen permeability coefficients obtained with a corrected equation that takes into account the boundary layers between the stacked lenses. (C) 1999 John Wiley & Sons, Inc.