The question of whether multi-purpose solution is the same as saline solution is a common source of confusion for contact lens wearers, but the two products are fundamentally different and serve distinct purposes in eye care. While both liquids appear clear, their chemical makeup and intended functions are not interchangeable. Understanding the role of each solution is necessary for maintaining healthy contact lens use and preventing eye irritation or infection.
The Role and Composition of Saline Solution
Saline solution is a simple, sterile mixture of purified water and sodium chloride, which is common table salt. This mixture is formulated to contain about 0.9% salt, making it isotonic because it closely mimics the natural salt concentration of human tears. The role of saline is passive hydration and rinsing, not active cleaning or disinfection.
Saline is used to rinse away debris or residual cleaning agents from the lens surface before insertion. It is also used for rewetting lenses to relieve dryness. Saline solution lacks active germ-killing ingredients, cleaning agents, or surfactants. Therefore, saline should never be used as the sole solution for cleaning, disinfecting, or storing contact lenses overnight.
Multi-Purpose Solution: Cleaning and Disinfecting Power
In contrast to saline, multi-purpose solution (MPS) is a complex product designed to perform multiple steps of the contact lens care routine simultaneously. The “multi-purpose” designation means it can clean, rinse, disinfect, and store soft contact lenses. This complexity is reflected in its diverse chemical composition, which goes far beyond just salt and water.
MPS contains several active ingredients, including chemical disinfectants designed to kill bacteria, fungi, and other pathogens. These solutions also include surfactants, which are detergent-like agents that help remove protein and lipid deposits from the lens surface. Buffering agents maintain a stable, eye-friendly pH, and wetting agents are added to increase comfort during wear. This combination allows MPS to effectively reduce the risk of microbial keratitis.
Why They Are Not Interchangeable
The difference between the two solutions lies in their ability to kill microorganisms, making them non-substitutable for proper lens hygiene. Using saline solution to clean or store contact lenses is dangerous because it fails to disinfect the lenses, allowing harmful pathogens to multiply. This inadequate disinfection significantly increases the risk of eye infections, which can sometimes lead to severe complications.
While multi-purpose solution can be used for rinsing, its active disinfecting ingredients and preservatives mean it is not ideal for excessive or repeated rinsing throughout the day. The chemical components that make MPS effective can sometimes cause irritation or sensitivity if used too frequently for simple rewetting. The difference is a matter of function: saline is a passive, gentle rinse, and MPS is an active cleaning and disinfecting system. Therefore, for contact lens storage and disinfection, only the multi-purpose solution or another approved disinfecting system should be used.