Corneal oxygen need and gas permeable contact lenses.

The minimum corneal oxygen need varies between 2 and 5% depending on individual characteristics. The tear pump alone is not sufficient to provide the corneal oxygen needs of many PMMA wearers. Hard permeable contact lenses may provide oxygen to the cornea by the tear pump and/or direct transmission through the lens. The relationship between the various oxygen permeable hard materials and the oxygen provided at the corneal surface is shown in this paper.