Wearing contact lenses overnight is generally not recommended, though the advice depends on the lens type. For most products, sleeping in contacts, even briefly, significantly increases the risk of serious eye health complications. Eye care professionals advise removing lenses before sleep, as overnight wear can increase the risk of a severe eye infection, such as microbial keratitis, by six to eight times. This danger stems from the eye’s physiology, which requires a constant supply of oxygen to maintain its health and clarity.
Why the Cornea Needs Constant Oxygen
The cornea, the clear, dome-shaped front surface of the eye, is unique because it is avascular (contains no blood vessels). It must obtain oxygen directly from the surrounding air to perform its functions and remain transparent. During the day, tears carry dissolved oxygen to the corneal surface. When the eyelid closes during sleep, the oxygen supply naturally drops significantly, forcing the cornea to rely on blood vessels in the inner eyelid.
Placing a contact lens over the eye creates an additional physical barrier to this reduced oxygen flow, causing corneal hypoxia. This oxygen deprivation compromises the cornea’s epithelial cells, the protective outer layer. Stressed cells lose their ability to effectively fight off bacteria and maintain the cornea’s normal fluid balance.
The lack of oxygen causes the cornea to swell (edema), which manifests as cloudiness or blurred vision. The reduced resistance allows microorganisms, trapped between the lens and the eye, to multiply rapidly. This creates an environment for developing microbial keratitis, a potentially blinding infection that can progress quickly.
Understanding Extended Wear and Daily Wear Lenses
Contact lenses are categorized into two main schedules: Daily Wear (DW) and Extended Wear (EW). Daily wear lenses are intended to be worn only while awake and must be removed and cleaned or discarded before any sleep period. These lenses are typically made from older hydrogel materials and are not designed to allow sufficient oxygen transmission for a closed eye.
Extended wear lenses are the exception, as they are specifically approved for continuous wear, including overnight. These lenses are manufactured using advanced silicone hydrogel materials, which dramatically increase oxygen permeability (Dk/t value). This high permeability is required to minimize the risk of oxygen deprivation while the eye is closed for an extended period.
While some EW lenses are approved for up to six nights of continuous wear, and a few for up to 30 days, their use must be closely monitored by an eye care professional. Even with these specialized lenses, the risk of developing a serious infection is still significantly greater than if the lenses were removed nightly. Overnight wear is generally reserved for situations where the benefits outweigh the increased risk and should never be initiated without a doctor’s explicit recommendation.
Warning Signs and Immediate Action
Recognizing the symptoms of an eye complication is necessary for anyone who wears contact lenses, especially if they have slept in them inadvertently. Key warning signs often present as a cluster of symptoms, indicating a possible infection or inflammation of the cornea. These symptoms signal a need for immediate attention.
Symptoms Requiring Immediate Care
If any of the following symptoms appear, the immediate action is to remove the contact lens, discard it, and seek emergency care from an optometrist or ophthalmologist:
- Sudden, persistent eye pain or burning
- Unusual redness that does not clear up quickly
- A feeling that something is constantly stuck in the eye
- Increased sensitivity to light (photophobia)
- Excessive tearing or discharge
- Vision that is suddenly blurred or noticeably reduced
Delaying professional treatment can allow a corneal infection to rapidly progress, potentially leading to irreversible vision loss or the need for a corneal transplant. The eye care provider will conduct an examination and initiate treatment, typically with prescription eye drops, to preserve sight. If a lens is stuck and dry upon waking, do not force it out; instead, lubricate the eye with rewetting drops or saline until the lens loosens before attempting removal.