The simple act of wearing contact lenses for too long, particularly sleeping in them, carries significant risks to eye health. Contact lenses are medical devices, and extending their wear time beyond the recommended schedule can severely disrupt the eye’s natural physiology. Improper use creates an environment ripe for complications, ranging from mild discomfort to severe, sight-threatening infections. Understanding these risks is necessary, as the consequences of misuse can be long-lasting or even permanent.
How Contact Lenses Affect Corneal Oxygen Supply
The fundamental reason contact lens overwear is dangerous lies in how the cornea, the transparent front dome of the eye, gets its oxygen. Unlike other body tissues, the cornea contains no blood vessels; it draws oxygen directly from the air through the tear film when the eyes are open.
A contact lens acts as a physical barrier that restricts this essential oxygen flow, leading to corneal hypoxia (oxygen deprivation). This restriction is compounded when sleeping in lenses because closed eyelids reduce the oxygen available to the cornea by up to two-thirds.
When deprived of oxygen, the cornea accumulates lactic acid, causing fluid to be drawn in and resulting in swelling (edema). While newer silicone hydrogel lenses allow greater oxygen transmission, they still do not eliminate the risk of hypoxia when worn against medical advice, especially overnight.
Common Signs of Overwearing
Initial warning signs of contact lens overwear indicate the cornea is under stress and should not be ignored. A frequent symptom is general eye redness (conjunctival injection), which occurs as blood vessels dilate to compensate for the lack of oxygen. Users may also experience pronounced dryness, as the lens material draws moisture from the tear film over an extended period.
A foreign body sensation, or a gritty feeling, signals irritation or minor damage to the corneal surface. Vision might become temporarily blurred or hazy, often resulting from minor corneal swelling (edema) or protein deposits on the lens surface. These symptoms require immediate removal of the lenses to allow the eye to recover.
Severe Ocular Complications
Prolonged or repeated contact lens overwear substantially increases the risk of serious, vision-threatening conditions. The most concerning is microbial keratitis, a severe corneal infection caused by bacteria, fungi, or the parasite Acanthamoeba. A lens worn too long can abrade the corneal surface, creating an entry point for pathogens trapped beneath the lens.
The combination of a compromised corneal surface, reduced oxygen, and a warm, moist environment allows microorganisms to proliferate rapidly. If untreated, microbial keratitis progresses into a corneal ulcer—an open sore on the surface. This ulceration can lead to permanent scarring, which blocks light from reaching the retina and causes irreversible vision loss.
Another serious long-term consequence of chronic oxygen deprivation is corneal neovascularization, where new blood vessels abnormally grow into the normally clear cornea. These vessels attempt to supply the oxygen-starved tissue, but their presence obstructs vision and signals chronic hypoxia. This condition is an irreversible structural change that often requires a permanent switch to glasses.
Immediate Steps When Eyes Are Irritated
If your eyes are irritated after wearing contacts for too long, immediately remove the lenses without delay. Do not attempt to clean or reinsert them, as this introduces more risk to an already stressed eye. Switch to wearing glasses exclusively to give the corneal tissue time to heal and re-oxygenate.
If discomfort is mild, using preservative-free artificial tears can help soothe and rehydrate the eye surface. However, seek immediate attention from an eye care professional if you notice urgent “red flags.” These include a sudden onset of severe pain, marked sensitivity to light (photophobia), or a noticeable decrease in vision.
The presence of a dense white or gray spot on the cornea signals a possible corneal ulcer and requires emergency medical evaluation. Persistent, severe redness or discharge lasting more than a few hours after lens removal signals a potential infection that must be treated quickly to prevent permanent damage.