Contact lenses correct vision and sit directly on the surface of the eye. For the vast majority of wearers, the fundamental rule for safe use is to always remove the lenses before going to sleep, including during short or long naps. This rule only changes if an eye care professional has prescribed a specific lens type for extended or continuous wear. Ignoring this instruction drastically increases the risk of serious complications for the delicate tissue of the eye.
Restricted Oxygen Flow to the Cornea
The cornea, the clear, dome-shaped front surface of the eye, is unique because it is avascular, meaning it contains no blood vessels. Instead, the cornea must absorb the oxygen it needs to function directly from the surrounding environment, primarily from the air through the tear film. When the eye is open, the cornea receives a full supply of oxygen from the atmosphere.
When a person closes their eyes to sleep, the oxygen supply to the cornea naturally drops significantly, relying on the limited oxygen transported from the blood vessels in the inner eyelid. This reduction in oxygen availability is further compounded by the presence of a contact lens. The lens material acts as an additional physical barrier, trapping a layer of tears and preventing the already-reduced supply of oxygen from reaching the corneal surface. This condition is known as corneal hypoxia, or oxygen deprivation.
How Lack of Oxygen Damages Eye Tissue
Corneal hypoxia results in the swelling of the cornea, a condition called corneal edema. The cornea’s outer layer absorbs excess water when it lacks sufficient oxygen to maintain its normal metabolic balance. This swelling can lead to a noticeable clouding of vision and a hazy appearance.
This lack of oxygen also compromises the integrity of the corneal epithelium, the outermost layer of cells. Small, invisible tears or abrasions can form on the corneal surface, which creates entry points for harmful microorganisms. Over time, chronic oxygen deprivation can trigger a defense mechanism in the eye called neovascularization. This involves the growth of new, fragile blood vessels from the periphery of the eye into the transparent cornea in a desperate attempt to deliver oxygen. These new vessels can impair vision by blocking the path of light.
Increased Risk of Microbial Keratitis
Microbial keratitis, a severe and sight-threatening infection of the cornea, is the primary health threat from sleeping in contact lenses. Studies indicate that sleeping in lenses can increase the risk of a contact lens-related infection by eight times or more.
The contact lens itself can harbor bacteria, fungi, or parasites that are trapped between the lens and the eye, which then have an open pathway into the compromised corneal tissue. Common pathogens involved include the bacteria Pseudomonas aeruginosa, which can cause rapidly progressing and destructive infections. Fungi and the single-celled amoeba Acanthamoeba can also cause keratitis, with the latter being particularly difficult to treat and frequently resulting in permanent vision loss. An untreated infection can quickly lead to a corneal ulcer, which is essentially an open sore on the cornea. In the most severe cases, the resulting corneal scarring necessitates a full corneal transplant to restore vision.
What to Do If You Fall Asleep in Lenses
If you accidentally wake up having slept in your contact lenses, do not immediately pull them out. The lenses are likely dehydrated and may be adhered to the corneal surface, and forcing them off can cause painful and damaging abrasions to the epithelium.
Rehydrate the eyes by applying several drops of sterile saline solution or rewetting drops. You should then close your eyes and gently massage the eyelids or blink repeatedly to help the drops loosen the lenses. Only attempt removal once the lenses move freely on the eye. After removal, wear glasses for the rest of the day to allow the cornea time to recover oxygen and heal. If you notice any persistent symptoms such as redness, pain, excessive tearing, or blurred vision that last for more than an hour after removal, you must contact an eye care professional immediately.