Contact lenses are medical devices manufactured with a defined shelf life indicated by an expiration date. Using lenses past this date compromises the careful balance of safety and material integrity engineered by the manufacturer. While the temptation to use an expired pair may be strong, the potential consequences to eye health far outweigh any perceived benefit. Understanding the factors that cause contact lenses to expire and the specific risks involved is crucial for protecting vision.
Why Contact Lenses Have Expiration Dates
The expiration date represents the final day the manufacturer guarantees the product’s safety and effectiveness. This guarantee relies on two factors: the maintenance of sterility and the integrity of the lens material. The lens is sealed in a blister pack filled with a sterile saline solution to keep it free of contaminants until use.
Over time, the protective foil and plastic seal of the blister pack can microscopically degrade, even if the package appears intact. These minute breaches allow oxygen, bacteria, or fungi to enter the previously sterile environment, contaminating the lens and the solution. The solution itself can also change chemical composition, losing its ability to maintain a sterile environment.
The physical composition of the lens material is the second factor necessitating an expiration date. Modern lenses are made from advanced polymers, such as hydrogel or silicone hydrogel, designed to allow oxygen to pass through to the cornea. This material can slowly degrade or change structure, affecting its water retention and oxygen permeability. Once the expiration date passes, the manufacturer cannot guarantee the lens will perform as intended or maintain necessary oxygen flow.
The Immediate Effects of Using Expired Lenses
Immediately after inserting an expired lens, the user is likely to experience physical discomfort related to material breakdown and moisture loss. The lens may have become brittle, warped, or less flexible due to changes in the packaging solution or the material itself. This structural change can cause the lens to fit poorly, leading to a gritty or foreign body sensation on the eye’s surface.
The reduced water content or altered surface often results in increased eye dryness and irritation. The eyes may appear red or feel itchy, responding directly to friction or compromised material. Blurred vision may also occur because the degraded lens is no longer maintaining its intended optical properties or precise shape. These effects can create small abrasions that make the eye vulnerable to more severe issues.
Serious Risks to Eye Health
The most significant danger stems from the compromised sterility of the packaging, which introduces harmful microorganisms directly onto the eye’s surface. A contaminated lens acts as a vector, trapping bacteria, fungi, or protozoa against the cornea, leading to microbial keratitis. This severe infection is a medical emergency that can cause intense pain, blurred vision, and light sensitivity.
If the infection is left untreated, it can rapidly progress to a corneal ulcer. A corneal ulcer is an open sore on the front surface of the eye, which can lead to permanent scarring and significant vision impairment. One feared infection is Acanthamoeba keratitis, a parasitic infection that is difficult to treat and strongly linked to non-sterile lens practices.
A serious risk is corneal neovascularization, caused by the reduced oxygen permeability of an aged lens. The cornea receives oxygen directly from the air, and if a lens blocks this flow, the eye compensates by growing new blood vessels into the corneal tissue. These abnormal vessels obstruct vision and can permanently change the cornea’s structure, potentially disqualifying the individual from future corrective procedures like LASIK. Oxygen deprivation and severe infections can result in irreversible scarring, potentially necessitating a corneal transplant or leading to permanent vision loss.
What to Do If You Have Worn Expired Contacts
If you realize you have worn expired contact lenses, remove them immediately and dispose of them, along with any remaining lenses from that expired box. Do not attempt to clean the lenses or store them in fresh solution, as the contamination risk is too high. Switch to wearing glasses to give your eyes rest and allow them to recover from any potential irritation or abrasions.
Monitor your eyes closely for any symptoms of infection or injury over the next 24 to 48 hours. Signs include persistent redness, pain that does not subside, excessive tearing, eye discharge, or increased light sensitivity. If any of these symptoms appear, contact an eye care professional, such as an optometrist or ophthalmologist, right away for a comprehensive eye exam. Seeking prompt medical attention is the best defense against an infection that could lead to long-term vision damage.