Permeability of hydrophilic contact lenses.

Oxygen permeability and water diffusion characteristics were determined for several types of hydroxyethyl-methacrylate hydrophilic contact lenses and a silicone contact lens material. A twoto fourfold difference in the diffusion rates for capillary flow of water was found among the different hydrophilic lenses. Oxygen permeability studies demonstrate that the hydrophilic lenses are capable of transmitting many times more than the calculated amount of dissolved oxygen in the capillary water flow if an oxygen partial pressure gradient exists across the lens. The silicone contact lens will transmit oxygen more than four times faster than will the most permeable hydrophilic lens; however, the silicone lens is almost totally impermeable to water and ostensibly impermeable to tears.