contact lens materials
Plasma Treatment Facts: No Sugar Coating
BY NEIL A. PENCE, OD, FAAO
In listening to speakers and representatives talk about plasma treatment of GP lenses, and in talking with practitioners as to their understanding of the process, I've heard varied interpretations. Many are under the impression that it's a coating applied to the surface. "Don't use abrasive cleaners, as they may damage this coating," is among the comments I've heard.
Perhaps a better understanding of GP lens plasma treatment will lessen some of the confusion that seems to exist about this process.
Plasma Treatment Explained
Plasma treatment of GPs is in fact approved as a cleaning method. It's extremely good at removing all the manufacturing contaminants and residues from lens surfaces, but it's not a coating.
Plasma is a highly excited, ionized gas. It's considered the fourth state of matter, in which free electrons are not bound to atoms. Plasmas can be highly conductive of electrical and magnetic energy and are characterized by the gas, the power source used to excite them and by atmospheric pressure and temperature.
In the case of GP lens plasma treatment, lenses are placed in a vacuum chamber. Oxygen is the gas, and it is excited by radio frequency energy. The ionized oxygen bombards and reacts with the oils and contaminants on the lens, freeing them from the surface. The plasma and contaminants are then drawn out as the vacuum is applied, leaving an extremely clean lens surface.
|Plasma treatment is good at removing manufacturing contaminants and residues, but it's not a coating.|
By varying the gas, energy, pressure or temperature, it would be possible to alter the lens surface. This may be a useful development in the future, but currently the treatment is simply a super cleaning.
Benefits of Plasma Treatment
Lenses are removed from the vacuum chamber already in the cap's lens holder, so they are placed in a vial containing contact lens solution to be shipped wet to practitioners without ever being touched. This maintains the cleanest, wettest surface possible, because a clean surface has improved wettability, which in turn translates into improved initial lens comfort. How long this initial advantage lasts is debatable, but even if relatively short-lived, improved initial comfort of GP contact lenses is a significant benefit.
Consider the usual scenario of lenses shipped dry in flat-packs. The lens surface is in contact with the lens case. Even if all the trace residues from the case molding process are removed (which may be difficult), the two plastic surfaces in contact have the potential to interact with one another. This is especially true when they are heated, which explains why we tend to receive more poor-wetting GP lenses in the hot summer months. This may result in a damaged lens surface — a problem that's eliminated when super-clean plasma-treated lenses are shipped wet.
You might need a physics degree to really understand plasmas, but hopefully not to find some interest in this discussion. Most importantly, we all may understand a little more about how this evolving technology can benefit our GP lens patients. CLS
To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #150.
Dr. Pence is director of the Contact Lens Research Clinic, Indiana University School of Optometry in Bloomington, Indiana.