Contact lenses designed for a two-week replacement schedule are medical devices regulated by bodies like the Food and Drug Administration (FDA). This strict 14-day timeline is not an arbitrary suggestion but is based on the physical and chemical limitations of the lens material. Adhering to the replacement schedule is necessary for maintaining the health and clarity of the cornea, the transparent outer layer of the eye. Wearing these lenses beyond the recommended period significantly increases the risk of complications, ranging from mild discomfort to severe, sight-threatening infections. The schedule exists to ensure the lens functions as intended, providing clear vision while allowing sufficient oxygen to the eye.
The Science Behind the Deadline
The reason two-week contact lenses have a fixed expiration is rooted in the material science of the lens itself. Over time, the lens material, whether a traditional hydrogel or a newer silicone hydrogel, begins to degrade and lose its intended properties. This degradation is accelerated by the constant presence of the tear film and the mechanical stress of blinking and handling.
A primary concern is the reduction in oxygen permeability, often measured as Dk/t. This measurement indicates how much oxygen can pass through the lens to the cornea. The cornea does not have blood vessels and relies heavily on atmospheric oxygen diffused through the tear film and the contact lens. As a lens ages, deposits build up and the material structure changes, restricting oxygen flow to the eye.
This problem is compounded by the accumulation of biological deposits from the eye’s natural tears. Tear components such as proteins and lipids adhere to the lens surface, creating a microscopic film. This buildup makes the lens surface rougher, inhibits oxygen flow, and reduces the lens’s ability to maintain its original shape and hydration. The cumulative nature of this deposition is why even rigorous cleaning cannot fully restore an overworn lens.
Immediate and Noticeable Effects
When a two-week lens is worn past its replacement date, the first signs are typically mild and related to physical irritation and poor lens quality. The accumulating film of protein and lipid deposits on the lens surface begins to disrupt the smooth interaction between the lens, the eyelid, and the tear film. This often leads to increased dryness and a persistent feeling of discomfort.
Many users report a foreign body sensation, as if a small piece of grit is constantly under the eyelid. The friction caused by the roughened lens surface can also induce a mild, temporary redness in the conjunctiva, the clear membrane covering the white of the eye. Temporary blurry vision may occur due to the uneven deposit accumulation, which scatters light and compromises the lens’s optical clarity. These symptoms are an immediate signal that the lens is failing its job and physically irritating the ocular surface.
The Threat of Serious Eye Infections
The increased susceptibility to severe, sight-threatening eye infections is a serious consequence of overwearing contact lenses. The buildup of deposits on the lens creates a fertile breeding ground for microorganisms, forming what is known as a biofilm. This film shields bacteria, fungi, and protozoa from the lens cleaning solution, allowing them to proliferate on the eye’s surface.
The combination of a contaminated lens and reduced oxygen flow to the cornea makes the eye vulnerable to a condition called Microbial Keratitis. This is an infection of the cornea that can be caused by common bacteria like Pseudomonas aeruginosa, which can rapidly destroy corneal tissue. Fungal and Acanthamoeba keratitis, though less common, are particularly difficult to treat.
A corneal ulcer, a localized open sore on the cornea, is the physical manifestation of a severe, untreated infection. These ulcers cause intense pain, significant inflammation, and can lead to permanent corneal scarring. Even with aggressive and prompt treatment, severe keratitis can result in irreversible vision loss and may necessitate a corneal transplant to restore sight.
Safe Practices and Emergency Action
Preventing the complications of overwear relies on strict adherence to established safety guidelines and the replacement schedule. The most effective preventative measure is to dispose of two-week lenses exactly 14 days after opening the package, regardless of how often they were worn.
- Practice meticulous hand hygiene by washing hands with soap and drying them thoroughly before handling the lenses.
- Never expose lenses or the case to water, including while showering or swimming, as tap water can harbor harmful pathogens like Acanthamoeba.
- Clean the lens case daily, allow it to air-dry, and replace it completely every three months to prevent contamination.
- Unless specifically approved by an eye care professional, avoid sleeping in any contact lens, as this dramatically compounds the risk of infection.
If you experience severe symptoms such as intense pain, sudden vision loss, light sensitivity, excessive tearing, or a thick discharge, immediate action is necessary. The lenses must be removed immediately, and you should seek emergency care from an eye doctor or ophthalmologist without delay. Prompt medical attention is the best defense against vision loss from a serious contact lens-related infection.