In situ oxygen transmissibility of rigid gas-permeable contact lenses.

On the eye a contact lens is bathed in tear fluid, which increases its resistance to oxygen flux. For rigid gas-permeable lenses, this effect should be small during open-eye wear because a large amount of oxygen is provided by air-saturated tears that are pumped under the lens. However, under closed-eye conditions this study suggests substantial decrease in overall lens system oxygen transmissibility when lens transmissibility itself is greater than 20 x 10(-9) cm ml O2/s ml mm Hg and when the average thickness of the tear layer is greater than about 20 micron.