Falling asleep while wearing contact lenses is common, but doing so safely depends entirely on the lens type. Contact lenses are categorized into two main groups based on their wearing schedule: Daily Wear (DW) and Extended Wear (EW). DW lenses must be removed nightly, while EW lenses are specifically designed and approved to be worn continuously, including overnight, for a set number of days. Understanding how these lenses allow your eye to breathe is essential for protecting your vision.
The Defining Difference: Oxygen Permeability
The cornea receives its oxygen supply directly from the air. When the eye is open, oxygen is readily available. However, when the eyelids close during sleep, the cornea must rely on limited oxygen diffusing from the blood vessels inside the lid. Placing a contact lens over the cornea creates a physical barrier that further restricts this oxygen flow.
The ability of a lens to allow oxygen to pass through is measured by its oxygen transmissibility, known as the Dk/t value. This value indicates the actual amount of oxygen reaching the cornea. If the lens does not have a sufficiently high Dk/t value, the cornea can become starved of oxygen, a condition called corneal hypoxia. This lack of oxygen can lead to discomfort, swelling, blurred vision, and increased susceptibility to infection.
Lenses Approved for Overnight Wear (Extended Wear)
The only contact lenses approved for overnight wear are Extended Wear (EW) lenses. These lenses are made from advanced materials, specifically silicone hydrogel, which significantly increases oxygen transmissibility compared to traditional hydrogel lenses. Silicone hydrogel incorporates compounds that create pathways for oxygen to pass through the lens more efficiently, allowing much more oxygen to reach the eye. This high Dk/t value helps prevent corneal hypoxia even when the eyelids are closed.
EW contacts are approved for two main schedules: up to six nights of continuous wear, or up to 30 continuous nights, depending on the specific brand and FDA approval. Lenses approved for the maximum 30-day schedule are sometimes referred to as continuous wear lenses. Even with these highly breathable materials, an eye doctor’s prescription is mandatory for EW use, and the lens must be removed and cleaned periodically as directed.
Being made of silicone hydrogel does not automatically mean a lens is approved for extended wear; many are intended only for daily wear. Even when using approved EW lenses, overnight wear carries a slightly elevated risk of eye infection compared to removing lenses every night. The decision to wear contacts overnight should always be based on a comprehensive examination and specific recommendation from an eye care professional.
The Risks of Misuse (Sleeping in Daily Wear Lenses)
Sleeping in contact lenses not approved for overnight use, such as standard Daily Wear (DW) hydrogel lenses, significantly increases the risk of serious eye complications. When a low-transmissibility lens is worn while sleeping, the closed lid and the lens create a warm, dark, and low-oxygen environment. This environment is ideal for the rapid multiplication of bacteria and other microorganisms trapped between the lens and the cornea.
The most severe risk is microbial keratitis, a sight-threatening infection of the cornea. Studies show that sleeping in any type of contact lens can increase the relative risk of this infection by over five times. This infection can lead to corneal ulcers, which are open sores on the eye’s surface. Ulcers cause extreme pain, significant vision impairment, and potentially permanent scarring or vision loss if left untreated.
If you accidentally fall asleep in your daily wear lenses, remove them immediately upon waking. If you experience symptoms like persistent redness, pain, excessive tearing, or blurred vision, seek prompt medical attention. Giving the cornea time to recover its oxygen supply is important, meaning the lenses should often not be reinserted for at least a full day.