The primary purpose of any CL care system has always been to protect the eye from potentially harmful microbial agents.
The primary purpose of any CL care system has always been to protect the eye from potentially harmful microbial agents that may accompany a CL onto the ocular surface.
The advance guard
Another early tool used to disinfect contact lenses was purified 3% hydrogen peroxide (H2O2). Still in use today, the first one-step hydrogen peroxide system was introduced in 1982.3
Hydrogen peroxide has been proven to be effective against a wide variety of organisms. Most bacteria are eradicated after 10 minutes of exposure to full strength H2O2. Elimination of fungi and protozoa require longer contact times, up to 60 minutes in some cases.
When neutralized, H2O2 is transformed into water and oxygen. When fully neutralized, no residual chemicals remain to potentially irritate the ocular surface. Consequently, hydrogen peroxide systems are often used today when it is suspected that a patient may be sensitive to chemicals in multipurpose systems.
Proactive versus reactive
Why is H2O2 generally used as a problem solver rather than a primary form of disinfection? There are a few reasons. First, since oxygen must be released during the neutralization process, a special vented case must be used, which can be inconvenient and may be messy if knocked over.
In addition, once the hydrogen peroxide is neutralized, the lens is soaking in a non-preserved solution. This opens the window for potential contamination if lenses are not re-disinfected regularly, such as on a daily basis. This can be a significant inconvenience for those who wear their lenses occasionally.
Finally, it has been my experience that too often lenses bathed in un-neutralized hydrogen peroxide end up being applied to the eye. Patients forget to neutralize. Friends and family grab the bottle without looking closely at it and apply it directly to their lenses. This leads to temporary, but significant, discomfort for the patient.
Convenience, then crisis
Multipurpose (MPS) CL care systems were introduced in 1995.1 The development of these systems was driven largely by convenience. The ability to clean, rinse, and disinfect lenses with a single solution is quite attractive to patients, and a challenging balancing act for manufacturers to deliver on. MPS solutions must kill microbes, yet be gentle to the ocular surface. They must be compatible with a wide variety of CL materials, and not sting when applied to the eye.
In addition to a quality of being comfortable to the eye, solution manufacturers began adding agents to MPS solutions to enhance the comfort of contact lenses during wear following storage in these products. This was motivated by the awareness that most patients reported discomfort as the primary reason they discontinued CL wear.4
In 2006, the CL community suffered an outbreak of Fusarium keratitis. It was eventually determined that the addition of a moisture-retaining ingredient to a particular solution contributed to the development of an environment that allowed for the survival of the Fusarium fungus.5