Whether contact lenses can be safely stored in normal saline is a common point of confusion for many wearers. While both normal saline and true contact lens solutions appear to be clear liquids, they are formulated for entirely different purposes. Normal saline is essentially a sterile saltwater solution, and this similarity to human tears often leads people to believe it is an acceptable substitute for lens care products. Understanding the difference between a simple rinsing agent and a multifaceted storage solution is necessary for maintaining eye health and avoiding potentially serious infections.
The Composition of Normal Saline
Normal saline is a solution composed of 0.9% sodium chloride, or salt, dissolved in sterile water. This concentration is isotonic, meaning it possesses the same salt balance and osmotic pressure as the natural fluids in the human body, such as tears and blood plasma. The primary medical purpose of this solution is to provide hydration, serve as a gentle rinse, or maintain sterility without causing cells to swell or shrink, a process known as osmotic shock.
The formulation of normal saline is simple, containing no active cleaning agents, surfactants, or dedicated antimicrobial components. While it is sterile when manufactured, it is not designed to maintain sterility or kill microorganisms over time once the bottle is opened. Therefore, normal saline’s function is limited to moistening or rinsing debris from a lens surface, not actively cleaning or disinfecting it. This lack of complex ingredients distinguishes it from the chemical composition of a multipurpose contact lens solution.
Why Saline Fails as a Storage Solution
Normal saline is unsuitable for storing contact lenses due to its inability to disinfect and clean the lens surface. Lenses worn in the eye naturally accumulate a biofilm composed of proteins, lipids, and calcium deposits from the tear film. Saline lacks the surfactants and chelating agents that specialized contact lens solutions use to break down and remove this organic buildup.
Storing lenses in a solution that cannot clean them results in a gradual reduction of lens breathability and comfort over time. The risk of microbial contamination is high, as saline provides a moist, non-hostile environment where bacteria, fungi, and even the dangerous parasite Acanthamoeba can multiply rapidly. Since normal saline has no antimicrobial activity, it cannot kill the pathogens transferred from the eye or the wearer’s hands to the lens case. Storing lenses in saline overnight essentially means soaking them in a potential culture medium, raising the risk of severe eye infections like microbial keratitis.
Proper Use and Emergency Alternatives
The acceptable function for normal saline in contact lens care is rinsing. It can be used to rinse a lens after it has been properly cleaned and disinfected, or to moisten a lens before insertion to flush away residual disinfecting solution that might cause irritation. It must not be used for long-term storage, disinfection, or as a substitute for contact lens cleaning agents.
For proper storage, wearers must use either a multipurpose solution, which cleans, disinfects, rinses, and stores, or a hydrogen peroxide-based system. If a person accidentally stores their lenses in normal saline overnight, the lenses must be considered contaminated. The immediate action is to remove the lenses and fully disinfect them in a proper multipurpose or hydrogen peroxide solution for the minimum recommended time, typically six to eight hours. If the lenses cannot be thoroughly disinfected immediately, the safest course of action is to discard them entirely and switch to glasses.