Although silicone hydrogels resemble conventional hydrogels because of the water that they contain, the substantial presence of relatively hydrophobic silicone components leads to many differences in behaviour from that of simple mid to high water content hydrogel lenses. In the four years since their launch, clinical experience has revealed a combination of characteristic benefits and complications (such as mucin balls and SEALS). There are three commercial materials; balafilcon A marketed under the trade name Pure Vision™ by Bausch and Lomb, lotrafilcon A marketed as Focus Night & Day™ by CibaVision and galyfilcon, marketed as Acuvue Advance™ by Vistakon. They have water contents of 24%, 36% and 47% respectively. The surface and bulk chemistries are significantly distinct from each other. The oxygen permeabilities of these three materials are well publicised and as expected, fall with increasing water content. The advantages associated with the trend to increased water contents has been less well appreciated, however, despite the fact that there now appears to be a trend in silicone hydrogel development away from lower water content materials. Evidence for this is found in FDA website information relating to new USAN names and new approval submissions, which reveals the development of new silicone hydrogels, such as senofilcon A (Vistakon), having a water content of 37%.
This poster compares the dynamic mechanical properties, dynamic wettability, and frictional properties of galyficon A, lotrafilcon-A and balafilcon-A (together with such other materials as become available for characterisation) in comparison to two reference points. The first of these is typical conventional hydrogel behaviour in the mid-water content range. The second is the human cornea. Taken together these properties provide a basis for interpreting the clinical behaviour of silicone hydrogels in comparison with conventional soft lens materials.