Water transport through soft contact lenses determined in a fan-evaporation cell

On-eye movement of commercial soft contact lenses (SCL) is crucial to the health of the cornea. Comfort and safety of a SCL lens depends on both the water content of and the water flux through the lens membrane. To acquire SCL water-permeability data, a newly designed fan-evaporation cell (FEC) is constructed. The fan-evaporation cell uses a more simple design compared to the previously used vacuum-evaporation cell for flat membranes . The new cell accommodates both commercial SCLs and flat-sheet membranes. After correcting for membrane thickness, measured water fluxes in the FEC agree with those obtained in the vacuum-evaporation cell (VEC) validating the new FEC. Ambient-temperature (23.5 °C) and on-eye (35 °C) gradient-driven water fluxes are reported for 10 commercial SCLs including both HEMA and silicone-hydrogel materials. For relative humidities less than about 75%, effective Fickian diffusivities of water in the hydrogels are about 3 × 10−7 cm2/s, essentially independent of lens material, saturated water content, and temperature. The effect of salt, mucin, and lysozyme on water-transport rates is minimal through Biomedics® 38, PureVision™, and Focus® DAILIES® lenses. However, lysozyme significantly reduces water flux through Acuvue 2 lenses.