Contact lenses are a widely adopted method of vision correction. For wearers, the question of whether to remove lenses before sleep is common. The answer depends entirely on the specific type of lens prescribed and the material it is made from. Understanding the lens design is the only way to determine a safe wearing schedule.
The Requirement for Daily Wear Lenses
Standard daily wear (DW) contact lenses must be removed before sleeping because they significantly restrict oxygen flow to the cornea. The cornea is avascular, meaning it receives oxygen directly from the air. When a lens covers the cornea, it acts as a barrier, causing reduced oxygen, or hypoxia.
This oxygen deprivation worsens when the eyelids close during sleep, cutting off the eye’s primary oxygen source. Chronic hypoxia can lead to the growth of abnormal blood vessels into the cornea, a condition known as neovascularization. Removing the lenses nightly allows the cornea to maintain the oxygen levels necessary for healthy function.
The nightly removal process also helps flush away accumulated debris and microorganisms. This prevents corneal swelling and maintains the eye’s natural defense mechanisms against infection. Daily wear lenses are not designed to withstand the closed-eye environment without compromising eye health.
Understanding Extended Wear Contacts
The exception to the daily removal rule involves lenses categorized as Extended Wear (EW) or Continuous Wear (CW). These lenses use advanced materials allowing for safe overnight use, often approved for periods up to 30 continuous nights. The key difference is their high oxygen transmissibility.
Modern extended wear lenses are predominantly made from silicone hydrogel, which is highly permeable to oxygen. This material enables a higher rate of oxygen to pass through the lens to the cornea. This minimizes the hypoxic stress that occurs when the eye is closed during sleep.
These lenses are only safe for overnight use if they have been specifically approved and prescribed by an eye care professional. Even with high oxygen transmissibility, the risk of complications, particularly infection, is still elevated compared to daily wear. Always adhere to the wearing schedule and replacement frequency recommended by your doctor.
The Dangers of Unapproved Overnight Use
Sleeping in lenses not approved for overnight wear significantly increases the risk of serious ocular complications. The warm, moist environment created when the eye is closed, combined with the lens, creates an ideal breeding ground for harmful microbes. This practice traps bacteria and reduces the cleansing action of tears, which normally wash away pathogens.
The most severe risk is microbial keratitis, a potentially blinding infection of the cornea. Individuals who sleep in their lenses have a six to eight times greater risk of developing this infection compared to those who follow proper guidelines. Infections like bacterial keratitis, often caused by Pseudomonas aeruginosa, can rapidly lead to a corneal ulcer and permanent scarring.
The physical presence of the lens on the closed eye can also cause microscopic abrasions on the corneal surface. These tiny tears provide an entry point for bacteria, accelerating the infection process. Even a short nap in daily wear lenses can increase this risk, requiring removal before any sleep.