Silicone hydrogel contact lenses represent one of the most important innovations in the recent history of contact lenses. This revolutionary new material imparts tremendous oxygen permeability to a contact lens. Because so many contact lens-related complications result from hypoxia, silicone hydrogel materials may prove more advantageous than HEMA-based hydrogels. Additionally, silicone hydrogel has proven itself beneficial to many dry eye patients.
As with any new technology, there is a learning curve. We're still discovering the properties, nuances and on-eye performances of these innovative materials. To properly care for them, it's important to develop a thorough understanding of them.
Silicone imparts tremendous oxygen permeability to a contact lens. Manufacturers have used silicone in GP and silicone elastomer lenses (SilSoft, Bausch & Lomb) for years. Only recently have we developed the capability of linking it to a hydrogel component. Unlike traditional hydrogels, where the oxygen permeability increases with higher water content, permeability actually increases as water content decreases -- allowing for more of the lens to include the more highly permeable silicone. In addition to greater Dk/t, silicone also imparts less dehydration and less protein deposition than traditional hydrogels. Pure silicone, meanwhile, is more rigid, more prone to lipid deposition and less wettable than HEMA. As a result, silicone hydrogel lenses may require either surface coatings or treatments to enhance wettability.
That was Then, This is Now
In the July 2003 issue, Dr. Jennifer Smythe wrote an excellent column (Contact Lens Care) on caring for silicone hydrogels. However, much has changed since then. At the time, only one silicone hydrogel lens was on the market; now four are available: Night & Day (CIBA Vision), O2Optix (CIBA Vision), PureVision (Bausch & Lomb) and Acuvue Advance (Vistakon); others are on the way.
One of Dr. Smythe's recommended solutions at that time, SoloCare (CIBA Vision), was later discovered to alter the diameter and power of Acuvue Advance and has since been discontinued. Two years ago, only Opti-Free Express (Alcon) had FDA approval for use specifically with silicone hydrogels. Today, the following three solutions contain the labeling indication:
1. Opti-Free Express Multi-Purpose Disinfecting Solution Lasting Comfort No Rub Formula
2. Clear Care (CIBA Vision)
3. Aquify 5 Minute Multi-Purpose Solution (CIBA Vision)
The labeling indication represents the efforts of companies to comprehensively test their products and report the results to the FDA. It doesn't mean that other solutions aren't compatible with silicone hydrogel materials. It's important to understand that when the FDA approved all three of these lens care products for this labeling, only one silicone hydrogel lens (Night & Day) was on the market. Although the FDA has not required testing with the other three materials to retain the labeling, no serious incompatibilities have been reported at this time.
Silicone hydrogel materials are different. Even though we lump them into one category, they are different and their care requirements may be unique to each material. I'll describe their similarities and differences -- as well as some of the latest research on lens care/material compatibilities -- in my next column, so stay tuned!
Dr. Gromacki is in group practice in Burke, Virginia, and has served as a faculty member at the University of Michigan Department of Ophthalmology and Visual Sciences.