contact lens materials
Comfilcon A: A New Silicone Hydrogel Material
BY LYNDON JONES, PHD, FCOPTOM, FAAO
The rapid growth in silicone hydrogels has made them the most widely fit type of lens material in certain markets. While these materials offer superb levels of corneal oxygenation, making hypoxic complications minimal during their use on both a daily and overnight wear schedule, they're not without their problems. These encompass mechanical and inflammatory complications and include epithelial splits, papillary conjunctival changes, epithelial erosions and sterile infiltrates.
We can attribute some complications to the technical difficulties encountered in producing lenses that contain siloxane compounds. Silicone hydrogels are inherently less flexible and have a more hydrophobic surface than do conventional HEMA-based hydrogels. In an attempt to overcome some of these difficulties, CooperVision recently launched a new silicone hydrogel lens, Biofinity, based on a novel silicone hydrogel material, comfilcon A (Table 1).
Comfilcon A contains two silicone-based macromers, one of which has a large molecular weight (M3U; nominal molecular weight 10,000 – 16,000). These macromers incorporated into a material with certain hydrophilic monomers result in a highly wettable lens with a low contact angle that requires no surface treatment.
This material has a high oxygen transmissibility (Dk/t), but still maintains a relatively low modulus (Figure 1). The breakage of this close link between modulus and Dk represents an important step forward in the development of silicone hydrogel materials.
To date, few publications have addressed the clinical performance of this new material. The overnight corneal swelling response is similar to that encountered with lotrafilcon A (Night & Day, CIBA Vision), and its clinical performance during continuous wear studies compares favorably with that of other materials approved for this use.
Figure 1. Graph of oxygen transmissibility (Dk/t) versus modulus for a variety of silicone hydrogels (green dots) and conventional lens materials (red dots).
As the lens becomes more widely available more data on its clinical performance will become apparent. CLS
To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #141.
Dr. Jones is the associate director of the Centre for Contact Lens Research and a professor at the School of Optometry at the University of Waterloo, Ontario, Canada.