Contact lens storage requires more than simply keeping the lenses wet. Saline solution, a sterile, buffered salt water mixture, is often confused with a complete storage solution. Saline alone is not appropriate for storing contact lenses, especially overnight, because it lacks the active ingredients necessary to clean and kill harmful microorganisms.
Understanding Saline Solution’s Purpose
Saline solution is a simple mixture of purified water and sodium chloride. It is formulated to be isotonic with natural tears, balancing the salt concentration to ensure comfort upon insertion. Its primary function in the contact lens care routine is rinsing the lenses.
Rinsing is performed after the lenses have been cleaned and disinfected to remove any lingering residue before insertion. Saline is also used as a rewetting drop to add moisture while the lens is being worn. Since it is pH-balanced and sterile, it is gentle on the eye, but this gentle nature is exactly why it is unsuitable for storage.
The Critical Need for Disinfection
Safe contact lens storage is primarily a process of thorough disinfection and cleaning, not just hydration. Lenses accumulate a microscopic layer of protein deposits, lipids, debris, bacteria, and fungi from the environment. Proper storage solutions are complex chemical systems engineered to address this contamination.
Multipurpose solutions, for instance, contain specific disinfectants that actively destroy pathogens during the soaking period. They also include surfactants, which are cleansing agents that lift and remove deposits from the lens surface. Without these active agents, the simple salt water of a saline solution allows microbes to survive and multiply, turning the lens case into a breeding ground. Hydrogen peroxide systems work differently, using a three percent solution of hydrogen peroxide to oxidize and break down pathogens, a process far more aggressive than inert saline.
Risks of Storing Lenses in Saline
Storing lenses in saline solution subjects the eye to significant health hazards due to the lack of antimicrobial activity. The lens becomes a vehicle for introducing high concentrations of microbes directly onto the cornea. This can rapidly lead to serious ocular infections, with microbial keratitis being a notable concern.
The absence of disinfectants also increases the risk of exposure to the resilient organism Acanthamoeba, which can cause a rare but sight-threatening infection that may require a corneal transplant. Furthermore, while saline keeps the lens wet, it lacks the conditioning agents found in true storage solutions that help maintain the lens material’s structure and hydration. If the saline solution evaporates, the lens can dry out, warp, and become damaged.