When contact lenses become dry and uncomfortable, the immediate reaction is often to search for a substitute liquid. While this discomfort is understandable, the delicate environment of the eye and the lens material itself demand specific care. No substitute can fully replace a commercially formulated contact lens solution for routine care and disinfection, and attempting to do so introduces significant risk. Proper solution is uniquely designed to maintain lens integrity and long-term ocular health, which is far more important than a momentary fix for dryness.
The Critical Need for Proper Saline and Sterility
Contact lenses require a surrounding liquid that is isotonic, meaning the solution contains the same concentration of salts and solutes as the eye’s natural tear film. Standard contact lens solutions are carefully engineered to match this physiological balance, which is approximately 0.9% sodium chloride. This balance prevents the lens from changing shape while it is off the eye. If a lens is placed in a hypotonic solution, like plain water, the lens material will absorb water, swell, and potentially distort, leading to a poor fit and corneal irritation upon reinsertion.
Beyond maintaining the lens structure, a proper solution is also formulated with disinfectants that actively kill bacteria, fungi, and other microbes that naturally accumulate on the lens surface during wear. The osmolality of these solutions, which can range from approximately 192 to 364 mOsm/Kg, is a primary factor in preventing adverse corneal effects and dry eye symptoms. Tap water and other non-sterile liquids completely lack these necessary disinfecting and buffering agents, allowing pathogens to proliferate rapidly.
High-Risk Substitutes to Never Use
The temptation to use common household liquids in an emergency poses significant and potentially permanent risks to vision.
Tap Water
Tap water is one of the most dangerous alternatives because it frequently harbors a microscopic organism called Acanthamoeba. If this amoeba adheres to the contact lens and is transferred to the eye, it can lead to Acanthamoeba keratitis. This is a rare but severe corneal infection that can result in permanent vision loss or blindness. Nearly 85% of these cases occur in contact lens wearers, and the main risk factor is exposing lenses to water.
Saliva and Distilled Water
Using saliva to moisten a lens is equally hazardous due to the high and diverse concentration of bacteria naturally present in the mouth. These oral bacteria can cause severe ocular infections when introduced to the eye. Distilled water should also never be used, as it is highly hypotonic, meaning it lacks any salt content. This severe difference in osmolarity causes the lens to rapidly absorb water and swell, potentially distorting its fit and increasing the risk of mechanical damage to the corneal surface.
Approved Temporary Rinsing and Rewetting Options
When the lenses become dry while they are being worn, the only safe and approved method for immediate relief is the use of dedicated rewetting or lubricating eye drops. These drops are specifically designed to be applied directly to the eye over the lens and are formulated to restore the natural moisture barrier without compromising sterility or lens material. Their chemical makeup closely mimics natural tears and is safe for use with all soft contact lenses.
If the lens needs a quick rinse while outside the eye, such as after accidentally dropping it, an over-the-counter sterile saline solution is the only appropriate choice. This saline is isotonic and sterile, making it safe for rinsing, but it contains no disinfecting agents and is not suitable for storage. Bottled water is still not sterile and should only be considered an absolute last resort for a momentary rinse, provided the lens is disinfected with proper solution immediately afterward.
The Absolute Danger of Improper Storage
While a temporary rinse can provide immediate relief, the nightly process of disinfection is a fundamental requirement for lens care that no substitute liquid can replicate. Improper storage, defined as placing lenses overnight in anything other than a dedicated disinfecting solution, is the fastest route to a severe eye infection. The purpose of overnight storage is not merely to keep the lens moist but to expose it to chemical agents that actively kill the microbes accumulated throughout the day.
Storing lenses in non-disinfecting liquids, even sterile saline or bottled water, allows bacteria and fungi to multiply exponentially on the lens surface and in the case. When these lenses are placed back on the eye, the wearer is directly inoculating the cornea with a concentrated dose of pathogens. The lack of a disinfecting agent means that any pathogen, including those that cause corneal ulcers, is permitted to thrive.
If you find yourself without proper disinfecting solution for overnight storage, the safest action is to either discard the lenses entirely or remove them and allow them to dry completely until you can purchase the appropriate disinfecting solution. The risk of corneal ulceration or severe infection from improper storage far outweighs the cost of replacing the lenses. Never rinse or store lenses in any type of water, including tap or sterile water, as this is a known risk factor for infection.