The question of whether one can sleep in monthly contact lenses is a common one that arises from the desire for convenience. Monthly contact lenses are prescribed for 30 days of use, but they must be removed, cleaned, and stored each night. For standard monthly lenses, the definitive answer from eye care professionals is no, they are not safe for overnight wear. This restriction is tied to the health and physiology of the eye, which requires an unobstructed supply of oxygen.
Standard Guidelines for Monthly Lenses
The designation of a monthly lens indicates approval for a 30-day replacement schedule, not 30 days of continuous wear. These standard lenses are typically made from older hydrogel materials that rely on water content to transport oxygen to the cornea. Oxygen transmissibility is measured by a technical value called Dk/t.
Standard daily-wear lenses are considered safe for use during waking hours if their Dk/t value is at least 24. When the eyelids close during sleep, the cornea’s oxygen supply naturally decreases. The material of a standard monthly lens further impedes the necessary oxygen flow, making overnight wear unsafe and violating manufacturer guidelines.
The Primary Health Risks of Sleeping in Contacts
Violating the recommended wear schedule introduces two primary and serious biological risks to the cornea. The first is corneal hypoxia, a condition where the cornea is starved of oxygen, which is a major concern when sleeping in contacts. The cornea, which is the transparent outer layer of the eye, receives nearly all of its oxygen supply from the air, not from blood vessels.
When a contact lens is worn overnight, it acts as a barrier, significantly reducing the oxygen reaching the cornea, causing it to swell, a condition known as edema. Chronic oxygen deprivation can lead to the abnormal growth of new blood vessels into the clear cornea, a process called neovascularization, which can permanently impair vision.
The second major risk is a severe eye infection known as microbial keratitis, which is an inflammation of the cornea. Sleeping in contact lenses can increase the risk of developing this infection by five to eight times. The lens traps bacteria and debris against the surface of the eye, while the lack of oxygen simultaneously compromises the cornea’s natural ability to fight off pathogens. This combination creates an environment highly conducive to infection, which, if left untreated, can lead to corneal scarring and vision loss.
Understanding Extended Wear Lenses
A separate category of contact lenses, known as Extended Wear (EW) or Continuous Wear lenses, is specifically designed and approved for overnight use. These lenses are distinct from standard monthly lenses because they are manufactured using a newer material, typically silicone hydrogel. This advanced material allows for significantly higher oxygen permeability.
Silicone hydrogel lenses incorporate silicone components to dramatically increase oxygen transmission. For a lens to be considered safe for overnight wear, it needs a Dk/t value of at least 87, though many eye care professionals prefer values over 100. These higher Dk/t values mimic the oxygen levels needed to maintain corneal health even while the eyes are closed. Even with these advanced materials, extended wear is only possible with a specific prescription and approval from an eye care professional, as the risk of infection, while reduced, is never fully eliminated.
Immediate Steps After Accidental Overnight Wear
If you wake up having accidentally slept in your standard monthly lenses, avoid panic and resist the immediate impulse to pull the lens out. The lens is likely dry and may be adhering tightly to the cornea, which could cause a painful abrasion upon removal. Instead, use sterile rewetting or lubricating eye drops to rehydrate the eye and the lens material.
Allow several minutes for the drops to fully soften and loosen the lens before attempting gentle removal. Once the lens is out, switch immediately to wearing glasses for at least 24 hours to give the cornea time to recover its oxygen supply and heal. Seek immediate medical attention if you experience symptoms like persistent pain, notable redness, sensitivity to light, or decreased vision.