Contact lens solution is an engineered liquid used to clean, rinse, disinfect, and store reusable contact lenses. Its primary function is to prevent harmful microorganisms from growing on the lenses and causing eye infections. The solution itself is not inherently detrimental, but problems arise when its chemical composition causes a reaction or when the user fails to follow proper hygiene protocols. When used correctly, the solution is an indispensable part of the contact lens wearing experience, keeping the lenses comfortable and safe.
When Contact Solution Becomes a Problem
The safety of contact lens solutions is often compromised by common user errors that weaken their disinfecting power. One frequent mistake is “topping off,” which involves adding new solution to the old liquid already in the lens case. The old solution contains microorganisms, proteins, and lipids shed from the eyes, and the disinfecting agents within it are already depleted. Adding fresh solution dilutes the active ingredients, creating a less potent mixture where germs can multiply instead of being killed.
A highly risky habit is the use of tap water, which is not sterile and contains microorganisms like Acanthamoeba. This amoeba can cause a rare but extremely painful and sight-threatening infection called Acanthamoeba keratitis. The minerals and impurities in tap water can also bind to the lenses, altering their fit and causing irritation.
Using solution past its expiration date means the disinfectant and preservative chemicals have degraded and are no longer guaranteed to be effective. This potency loss allows for the proliferation of bacteria, fungi, and other pathogens, significantly increasing the risk of serious eye infections like keratitis. Failure to clean the lens case itself is another major issue, as a dirty case can harbor a biofilm that resists disinfection and contaminates freshly cleaned lenses.
Signs of an Adverse Reaction
An adverse reaction to contact lens solution, whether due to chemical sensitivity or improper use, manifests with several noticeable symptoms. The most common signs are persistent redness and a burning or stinging sensation immediately upon inserting the lenses. This discomfort is often a direct result of the solution irritating the surface of the eye. Other symptoms include excessive tearing, increased light sensitivity, and blurred vision. Some individuals may experience a gritty sensation, which can indicate corneal changes or protein buildup. If the reaction is allergic, the eyelids may become swollen, and discharge might be present.
Understanding Chemical Sensitivities
Even with perfect hygiene, some people react poorly to the chemical composition of standard multipurpose solutions. These solutions rely on various ingredients, including surfactants to clean and buffering agents to maintain a balanced pH, but preservatives are the most common source of irritation. Preservatives are necessary to keep the solution sterile after the bottle is opened, but they can sometimes trigger an immune response or toxicity.
Modern multipurpose solutions often use large-molecule preservatives, such as polyhexamethylene biguanide (PHMB), polyaminopropyl biguanide, and polyquaternium-1 (Polyquad). These compounds work by disrupting the cell membranes of microorganisms. However, they can also interact with the corneal cells of sensitive users, causing solution-induced corneal staining (SICS). This reaction is a form of preservative-related toxicity that can lead to discomfort, dryness, and inflammation of the eye’s surface.
PHMB and Polyquad are generally considered safer than older preservatives like thimerosal. However, PHMB and related biguanides can still cause allergic contact dermatitis in some individuals, affecting the eyelids and surrounding skin. The concentration and specific combination of these biocides in multipurpose solutions determine the likelihood of an adverse ocular surface event in a susceptible individual.
Selecting Safer Alternatives
For individuals who experience persistent irritation or sensitivity to multipurpose solutions, switching to a preservative-free system can resolve the discomfort. Hydrogen peroxide solutions, typically containing 3% hydrogen peroxide, are a highly effective alternative that does not rely on traditional preservatives. The hydrogen peroxide acts as a strong disinfectant, breaking down proteins and killing a broad spectrum of microbes, including the dangerous Acanthamoeba.
This system requires a mandatory neutralization step before the lenses can be safely worn. The lenses are soaked in a special case containing a platinum-coated disk or a neutralizing tablet, which converts the hydrogen peroxide into a harmless saline solution over several hours, typically six. It is important not to skip this neutralization process, as un-neutralized hydrogen peroxide can cause intense stinging, burning, and damage to the corneal surface.
Another option for reducing solution dependency is to switch to daily disposable contact lenses, which are discarded after a single use and eliminate the need for cleaning or storage solutions entirely. Saline solution is useful only for rinsing the lenses before insertion but must never be used as a disinfectant, as it contains no germ-killing agents. Before making any change to a lens care regimen, individuals should always consult with an eye care professional to ensure the chosen solution is compatible with their specific lens material and eye health needs.