It is strongly advised against using contact lens solution as a substitute for eye drops, despite both liquids being formulated for use in the eye. These products serve fundamentally different functions, optimized for distinct purposes. Contact solution is primarily designed to clean and disinfect plastic lens material, while lubricating eye drops are made to soothe and moisturize the biological surface of the eye. Using contact solution as eye drops can lead to irritation and potential harm because the cleaning ingredients are not suitable for direct application to delicate eye tissue.
The Core Difference in Formulation
The chemical differences between the two products explain why contact lens solutions (CLS) should not be used as eye drops. Multipurpose CLS often contain robust preservatives necessary for disinfecting lenses, such as polyhexanide or polyquaternium-1, which can be too harsh for the cornea when applied directly. These disinfectants are designed to kill microorganisms that grow on a contact lens, contrasting sharply with the gentle nature of lubricating drops. Eye drops are carefully balanced to match the eye’s natural tear film, including precise control over tonicity and pH.
Lubricating drops are formulated to be isotonic, meaning their salt concentration is similar to natural tears, helping to prevent stinging or burning. They also maintain a pH level close to the eye’s natural environment to maximize comfort. Many eye drops include thickening agents like hyaluronic acid or carboxymethylcellulose to increase viscosity, which helps the solution remain on the eye’s surface longer for sustained comfort and moisture. Contact solutions lack these viscosity agents because their purpose is not long-term lubrication.
Contact Solution’s Intended Role
The primary purpose of a multipurpose contact lens solution is to clean, rinse, disinfect, and store soft contact lenses. This involves actively removing protein deposits, debris, and microbes that accumulate on the lens surface during wear. The solution’s formula is optimized to interact with the plastic polymers of the lens, ensuring the material remains hydrated and clear while eliminating harmful pathogens.
This cleaning and disinfecting role requires chemical agents, such as surfactants and preservatives, that are highly effective against bacteria and fungi. These agents are safe for the eye only after they have been thoroughly rinsed off the lens or neutralized, not for direct, prolonged contact with the cornea. Lubricating eye drops, in contrast, simply supplement the natural tear film, providing a soothing layer of moisture without the aggressive cleaning action needed for a synthetic lens.
Saline vs. Lubricating Drops and Safety Risks
A common confusion exists between simple saline solution and multipurpose contact solution, but neither is interchangeable with lubricating drops. Saline is a simple salt-and-water solution used primarily for rinsing lenses. While it is closer to the composition of tears, it contains no active buffers or thickening agents to provide lasting comfort. Using plain saline offers only momentary rinsing relief because it lacks the necessary viscosity and moisturizing components of a true lubricating drop.
The safety risks of using a multipurpose contact solution directly in the eye are significant and often immediate. The presence of robust preservatives can cause corneal irritation, leading to stinging, burning, redness, and discomfort. In severe cases, particularly with hydrogen peroxide-based solutions that have not been properly neutralized, the chemical components can cause damage to the surface of the eye. Only products specifically labeled as “ophthalmic solutions” or “lubricating eye drops” have the proper formulation to safely and effectively moisturize and soothe the eye’s delicate tissues.