Contact lenses offer clear vision without the need for glasses, but their convenience is strictly limited to waking hours. Eye care professionals strongly advise against sleeping in contact lenses because it significantly increases the risk of serious eye complications. This prohibition applies to most standard daily-wear and two-week lenses, which are not designed to be worn while the eyelids are closed. Failing to remove these devices before sleep exposes the eyes to problems ranging from simple irritation to severe, sight-threatening infections.
The Role of Corneal Oxygen Deprivation
The cornea, the clear, dome-shaped front surface of the eye, is avascular, meaning it contains no blood vessels. It must draw its necessary oxygen directly from the surrounding air, a process called corneal respiration. When the eye is open, the cornea receives oxygen through the tear film. A contact lens places a barrier over this surface, restricting the natural flow of oxygen even while the wearer is awake.
When the eyelids close during sleep, the oxygen supply to the cornea naturally drops to about one-third of the open-eye level. If a contact lens is worn, it acts as an additional barrier, drastically reducing the oxygen supply further. This severe lack of oxygen is known as corneal hypoxia. Hypoxia causes the cornea to swell, and the body may trigger the growth of new, abnormal blood vessels into the clear corneal tissue, a condition called neovascularization.
The Serious Risk of Microbial Keratitis
The low-oxygen environment created by sleeping in contact lenses is a major precursor to severe infection and inflammation. When the cornea is oxygen-deprived, its ability to repair minor surface abrasions and defend against pathogens is compromised. The contact lens can also trap debris and microbes against the compromised corneal surface, creating a perfect breeding ground for colonization.
The most serious outcome is microbial keratitis, a painful corneal infection that can lead to permanent vision loss. This infection is often caused by bacteria, such as Pseudomonas aeruginosa, fungi, or the amoeba Acanthamoeba. Sleeping in contact lenses increases the risk of developing this type of eye infection by six to eight times. If the infection progresses, it can form a corneal ulcer, which is an open sore on the eye’s surface. Severe cases may require intensive antibiotic treatment, surgical intervention, or a corneal transplant.
The Distinction of Extended-Wear Lenses
Some contact lenses are specifically approved for overnight use and are categorized as extended-wear or continuous-wear lenses. The ability to wear these lenses while asleep is due to the advanced materials used in their construction, primarily silicone hydrogel. Unlike older hydrogel lenses that rely on water content for oxygen transfer, silicone hydrogel incorporates silicone, which allows significantly more oxygen to pass directly through the lens material.
These lenses are engineered to have high oxygen permeability, often measured by a Dk value over 100, which is sufficient to maintain corneal health even with the eyelids closed. Despite this enhanced breathability, wearing extended-wear lenses overnight still carries a higher risk of infection compared to removing lenses every night. Continuous wear is not a risk-free option and should only be undertaken with the explicit recommendation and monitoring of an eye care professional.
Protocol After Accidental Overnight Use
If you wake up having accidentally slept in your contact lenses, avoid immediate, forceful removal. The lens is likely dry and slightly adhered to the cornea, and pulling it off can cause surface damage or abrasions. The first step is to gently rehydrate the eye and the lens by applying a few drops of sterile saline or contact lens rewetting drops.
After allowing a few minutes for the lens to re-moisten and loosen, you can then attempt a gentle removal. Once the lenses are out, they should not be reinserted; the eyes need a minimum rest period of at least 24 hours to recover and receive adequate oxygen. It is imperative to monitor the eye for any signs of complication, such as persistent redness, worsening pain, excessive watering or discharge, or increased sensitivity to light. The appearance of any of these symptoms warrants an immediate consultation with an eye doctor.