Contact lens solutions are highly engineered products designed for disinfection, cleaning, and hydration. These functions are necessary because lenses sit directly on the sensitive cornea. The correct solution uses a complex mixture of disinfectants, surfactants, and wetting agents to remove debris and kill microorganisms. Maintaining this careful balance is paramount for long-term eye health, meaning commercial solutions are the only acceptable routine practice. Understanding the extremely limited emergency alternatives is necessary only when the correct solution is unavailable, to avoid significant eye damage.
Why Common Household Liquids Are Unsafe
The impulse to use common household liquids as a temporary substitute presents a serious risk to eye health. These alternatives lack the necessary sterility and possess an improper salt balance, known as tonicity.
Tap water is a highly dangerous substitute because it is not sterile and often contains microorganisms, including the microscopic amoeba Acanthamoeba. Tap water exposure is the main risk factor for Acanthamoeba keratitis, a rare but potentially sight-threatening infection. Furthermore, tap water is hypotonic, meaning it has a much lower salt concentration than the eye’s natural tear film. When a soft contact lens is placed in hypotonic water, the lens material absorbs the water, causing it to swell and change shape, which can lead to a tight fit and damage the corneal surface.
Bottled or distilled water, even if purified, is not formulated for ophthalmic use and lacks the antimicrobial agents required for disinfection. Like tap water, these liquids do not have the proper tonicity, and they can harbor pathogens that become dangerous when trapped against the cornea by a contact lens.
Using saliva to moisten or store lenses is extremely dangerous because the mouth is home to a dense population of bacteria that can easily be transferred to the lens and subsequently to the eye. This practice dramatically increases the risk of severe bacterial infection. Attempting to create a homemade saline solution by mixing salt and water is strongly discouraged because it is impossible to achieve the necessary sterility and precise tonicity outside of a controlled laboratory environment. The resulting solution will be non-sterile, and any undissolved salt crystals or improper concentration can scratch or severely irritate the cornea.
Safe Options for Temporary Storage
In a true emergency, acceptable options for a soft contact lens are extremely limited and should only be used for temporary storage or rinsing, not disinfection. The best short-term solution is a sterile, unpreserved saline solution. This solution is isotonic, meaning it matches the salt balance of the eye, which prevents the lens from swelling or shrinking.
Sterile saline is for rinsing and hydration only; it contains no disinfecting agents. Lenses stored in saline alone must be thoroughly disinfected with a proper multipurpose or hydrogen peroxide solution for the full recommended time before being worn again. If sterile saline is unavailable, a clean, unopened bottle of artificial tears or re-wetting drops designed for contact lenses can be used to rinse or temporarily hydrate the lens.
These drops are formulated to be safe for the eye but are not sterilizing solutions and should never be used for overnight storage. The lens must be transferred to a proper disinfecting solution as soon as possible, or it should be discarded entirely. If no sterile liquid alternative is available, removing the lenses and storing them dry in a clean, empty case is the safest option, as a dry lens cannot harbor active microbes. The dry lenses must then be soaked in a proper disinfecting solution for a minimum of four hours to rehydrate and sterilize them before reinsertion.
Health Risks of Improper Lens Care
Using non-sterile or improperly balanced solutions can lead to serious and painful medical conditions. Microbial keratitis, an infection of the cornea, is the most common complication, caused by bacteria, fungi, or parasites introduced by poor hygiene. Symptoms include severe eye pain, redness, blurred vision, discharge, and sensitivity to light. If left untreated, this condition can quickly cause corneal scarring and permanent vision loss.
The severe risk associated with tap water is Acanthamoeba keratitis, a parasitic infection that is notoriously difficult to treat. The amoeba can adhere to the lens surface and survive for long periods, leading to persistent infection. This condition is serious, with a high percentage of cases requiring an emergency corneal transplant due to the extensive damage caused to the eye’s surface.
Improper tonicity, such as using pure water, can also directly damage the ocular surface, even without introducing an infection. When the lens swells, it can adhere tightly to the cornea, and the mechanical removal process may strip away the delicate corneal epithelium, resulting in painful abrasions or ulcers. Furthermore, exposing lenses to liquids with an unsuitable pH or harsh chemicals can permanently degrade the lens material itself. This degradation causes the lens to become brittle or cloudy, leading to irritation and reduced visual clarity when worn.