The question of whether it is acceptable to wear expired contact lenses has a clear and definitive answer: no, it is not safe. The expiration date printed on the packaging is not merely a suggestion; it represents the final date the manufacturer guarantees the product’s sterility and physical integrity. Using lenses past this date introduces significant risks to eye health.
Why Contact Lenses Have Expiration Dates
The expiration date serves as a safety deadline due to the sealed packaging and the solution within it. Lenses are sealed in a buffered saline solution within an air-tight blister pack to ensure a sterile environment. This sterile condition is guaranteed only until the printed expiration date, typically set between one and four years from manufacture.
Over prolonged storage, the integrity of the packaging begins to decline. The foil seal, designed to prevent microbial contamination, can degrade. This degradation may create microscopic channels or leaks, allowing air, moisture, or microorganisms to enter the solution.
Once the seal’s integrity is compromised, the lens is no longer guaranteed to be germ-free. The saline solution, which keeps the lens hydrated, can undergo chemical changes over years of storage. This shift may alter the solution’s pH, potentially affecting the lens material and the eye’s surface.
The Immediate Health Hazards of Expired Lenses
The most immediate danger of wearing an expired contact lens is the risk of introducing contamination. If the packaging seal has failed, the lens becomes a breeding ground for microorganisms. This contamination is not always visible, yet it poses a serious threat to the cornea.
Wearing a non-sterile lens can lead to aggressive eye infections, such as bacterial keratitis. Keratitis is an inflammation of the cornea that can be painful and cause rapid vision loss if not treated. Certain bacteria, like Pseudomonas aeruginosa, are fast-acting, capable of causing a severe corneal ulcer within a day.
Fungi and other pathogens can colonize the lens and its solution once sterility is lost. Fungal keratitis, while less common, is difficult to treat and requires prolonged medical intervention. These infections cause inflammation, redness, and discharge, signaling a serious health emergency.
The risk of infection is compounded because expired lens material may cause tiny abrasions on the cornea. These micro-scratches act as entry points, allowing bacteria or fungi to penetrate the eye’s surface layers more easily. The outcome can be corneal scarring, which may lead to permanent visual impairment.
How Lens Material Degradation Affects Eye Comfort and Safety
Independent of sterility issues, the physical material of the lens deteriorates over prolonged storage. Lenses, whether hydrogel or silicone hydrogel, are made of permeable polymers engineered to allow oxygen to reach the cornea. This oxygen permeability is measured by the Dk/t value.
As years pass, the polymer structure of the lens can change, even while sealed. The material may lose its designed flexibility, causing the lens to become stiffer or more brittle. This structural change leads to a poor fit on the eye, increasing friction with the eyelid during blinking.
This poor fit and increased friction often cause irritation, redness, and discomfort. Material degradation can also reduce the lens’s ability to maintain hydration and shape, compromising the intended oxygen flow. Reduced oxygen flow to the cornea, known as hypoxia, can lead to corneal swelling, or edema.
Corneal edema can cause hazy vision and, over time, may trigger the growth of new blood vessels into the cornea, a serious condition called neovascularization. These physical changes in the expired lens material make it uncomfortable to wear and dangerous for corneal health.