New siloxane hydrogel contact lenses have enabled considerable leaps in the oxygen transmission capabilities of soft contact lenses. However, the numbers cited for oxygen transmissibility are calculated from the central thickness of a -3.00D lens, which gives the highest number. This does not take into consideration the transmissibility across the rest of the lens, which is dependent on its design.

Silicone hydrogel lenses, and for comparison, a widely used ordinary hydrogel lens, were sectioned and the thickness measured over the diameter of the lenses using a high resolution microscopic measurement technique previously described1. The thicknesses were used to profile the oxygen transmissibility perpendicular to the posteriour surface of the lenses across a section of the lens, and this is presented graphically. The mean of these values, based on harmonic mean lens thickness2 and the manufacturers' cited Dk, were 139.1, 74.8, and 22.2. x 10-9 barrers/cm for the two lenses tested and an ordinary soft lens control respectively. The maximum transmissibility at the thinnest part of the lens was 191.8, 101.5, and 32.7, x 10-9 barrers/cm respectively.

Oxygen transmission with the new siloxane hydrogel lenses have been increased by a maximum factor of approximately six times over ordinary hydrogel lenses for both the central and mean values, making it possible to satisfy even the most stringent estimates of the corneal oxygen requirements for contact lenses during sleep.