GP Fitting Case 1 - Discussion Item 4

a) In the late 1970's researchers used the durability of the PMMA (conventional hard lens material) as a backbone, then added silicone (siloxane) for more oxygen transmissibility resulting in a lens category known as Silicone Acrylates. This was a great breakthrough in contact lenses, but a concern was that the silicone would render the lens surfaces less wettable, thus making them more prone to deposit formation and potentially decreasing comfort. These Silicone Acrylate oxygen permeable materials had a Dk of 12-54. back

b) Greater amounts of silicone were added to these materials in an attempt to increase oxygen for longer wear (in some cases even extended wear). More silicone had some negatives though, such as less stability, poorer wetting and greater deposit adherence. back

c) Fluorine was added to the silicone acrylate materials creating a category known as Fluorosilicone Acrylates (FSA). These materials can have a Dk of 30-120. This is the main GP material category today. back

d) Today's high Dk materials are very stable, especially as compared to earlier generation GP materials, allowing manufacturers to make lens designs thinner with less overall mass and as a result more comfortable to wear. Also many potential problems like 3-9 staining, flexure and poor surface wetting is reduced or eliminated by the new materials and accompanying designs. back