Contact lenses require strict adherence to a wearing and cleaning schedule. When lenses are worn beyond the recommended time, especially overnight, the eye’s delicate biology is immediately compromised. The cornea, the transparent front dome of the eye, relies almost entirely on oxygen absorbed directly from the air and the tear film. Misuse, such as sleeping in lenses, creates a physical barrier that starves the cornea of this oxygen supply, setting the stage for adverse physiological events.
The Immediate Physiological Stress
The immediate consequence of overwearing contacts is corneal hypoxia, a state of oxygen deprivation. A contact lens significantly reduces the transmission of oxygen, especially when the eyelids are closed during sleep. This lack of oxygen forces corneal cells to shift to a less efficient anaerobic process, leading to the buildup of metabolic waste like lactic acid and carbon dioxide.
This waste accumulation creates an osmotic gradient that draws water into the cornea, resulting in corneal edema, or swelling. This swelling causes the temporary blurred or hazy vision often seen after overwear. The lens can also compromise the natural flow of tears, leading to severe dryness and mechanical irritation.
The Danger of Microbial Invasion
Physiological stress caused by hypoxia weakens the eye’s natural defenses, creating an environment for dangerous infections. When the cornea is swollen or irritated, the epithelial barrier is compromised, making it easier for microorganisms to invade the tissue. This increases the risk of microbial keratitis, a potentially blinding infection of the cornea.
Contact lenses become breeding grounds for pathogens, as the surface allows for the development of a protective layer called a biofilm. This sticky matrix shields microbes like bacteria, fungi, and protozoa from cleaning solutions and the eye’s immune system. When the lens is left in, this microbial colony is pressed against the stressed cornea, increasing the likelihood of invasion and potentially leading to a corneal ulcer.
Long-Term Structural Damage
Chronic contact lens overwear can lead to permanent changes in the eye’s physical structure. One consequence of persistent oxygen deprivation is corneal neovascularization, where the eye attempts to compensate by stimulating the growth of new blood vessels. These fragile vessels grow from the limbus into the normally clear corneal tissue, which can cause the cornea to lose its transparency and impact vision.
Another common chronic condition is Giant Papillary Conjunctivitis (GPC). GPC is an inflammatory reaction where small, dome-shaped bumps form on the inner surface of the upper eyelid. This is generally an allergic response to protein and lipid deposits accumulating on the lens surface, leading to chronic irritation and potentially making future contact lens wear difficult.
Recognizing Warning Signs and Emergency Care
Contact lens wearers must recognize symptoms that indicate a serious complication requiring immediate attention. Any persistent or sudden onset of severe eye pain or discomfort should be treated as an emergency. If symptoms appear, the lenses must be removed immediately and not reinserted, followed by a prompt consultation with an eye care professional.
Warning signs include:
- Excessive redness.
- A sudden decrease or blurring of vision.
- Unusual sensitivity to light (photophobia).
- Any discharge, such as pus or excessive tearing.
Prevention relies on strict hygiene, including always washing hands before handling lenses and adhering to the prescribed replacement schedule. Following the manufacturer’s and doctor’s guidelines for wear time and daily removal is the most effective way to protect the cornea and maintain vision health.