Inflammatory Events and Silicone Hydrogels
By Jason J. Nichols, OD, MPH, PhD, FAAO
In a general sense, inflammation is the body’s response to protect itself, ultimately leading the healing process. Inflammation can be acute or chronic and involves several of the body’s systems. However, it is important to consider that this response is a complex biological process that is multi-faceted. Likewise, it should also be noted that inflammation can be prompted by many stimuli—pathogens, damaged cells, chemical irritants, hypoxia, hypercapnia, temperature, radiation, mechanical or physical interactions, and even psychosocial issues—just to name a few triggers.
It is commonly known that silicone hydrogel lenses were developed to increase the oxygen availability to the cornea through the polymer. In this regard, these materials were intended to help alleviate hypoxic complications associated with lower-oxygen-permeable materials, including inflammatory events. However, some have begun to question the long-term success of the silicone hydrogel class of materials.
For instance, some adverse events such as contact lens-related microbial keratitis appear to be virtually unchanged, while others appear to be on the rise. Clinical experience and several studies have shown that silicone hydrogel materials are associated with at least a two-fold increase in the frequency of corneal infiltrative events compared with non-silicone hydrogel lenses (Szczotka-Flynn, 2007; Chalmers et al, 2011; Chalmers et al, 2012; Radford et al, 2009). This has completely baffled clinicians and scientists alike as these materials were developed to reduce a presumed stimulus to corneal inflammation—hypoxia!
However, more work needs to be conducted to cultivate our basic etiological understanding of this potential issue between silicone hydrogel materials and inflammation. The clinical studies referred to above show “associations” between the material and inflammation, but this is not the same thing as scientifically showing “cause and effect.” Without question, there is more work to be done—it’s too soon to close the book on the silicone hydrogel materials, particularly as this and several other chapters are still being written.
For references, please visit www.clspectrum.com/references.asp and click on document #205.