Polymers in contact lens applications VI. The ‘dissolved’ oxygen permeability of hydrogels and the design of materials for use in continuous-wear lenses

The ‘dissolved’ oxygen permeabilities (Pd) of a range of hydrogels have been studied at 25 and 34°C (the temperature of the eye). At both temperatures the equilibrium water content (W) was found to be the major controlling factor in determining oxygen permeability and log (Pd) was found to be linearly related to W. The values of Pd at 34°C were found to be approximately twice those at 25°C throughout the range of water contents studied. Available information on corneal oxygen consumption rates is used as a basis for the prediction of oxygen permeability/thickness requirements in continuous wear lenses. These data lead in turn to predicted minimum equilibrium water contents for hydrogels in this, type of application.