Monthly contact lenses are a popular option for vision correction, offering the convenience of a single pair lasting up to 30 days before replacement. These lenses are designed for daily wear, which explicitly requires removal every night before sleep. Understanding the physiological needs of the eye and the materials used in these lenses is necessary to follow the correct safety guidelines.
Why Standard Monthly Lenses Are Not Designed for Sleep
Standard monthly lenses should not be slept in, as they are not approved for overnight use. The cornea, the clear front surface of the eye, is unique because it is avascular. Instead, it receives oxygen primarily from the air when the eyes are open.
When the eyelids are closed during sleep, the oxygen supply to the cornea is already significantly reduced, drawing solely from the blood vessels in the inner eyelid. Standard monthly lenses, which are typically made from hydrogel or older silicone hydrogel materials, act as an additional barrier. This combination of a closed eyelid and a less permeable lens material can lead to a condition called hypoxia, or oxygen deprivation.
Corneal hypoxia can trigger several adverse effects, beginning with corneal edema, which is a noticeable swelling of the corneal tissue. This swelling can temporarily blur vision and compromise the structural integrity of the cornea. In chronic or severe cases of oxygen deprivation, the eye may attempt to compensate by growing new blood vessels into the cornea, a serious condition known as neovascularization.
A low-oxygen environment also creates an ideal breeding ground for microorganisms, dramatically increasing the risk of infection. When the cornea is compromised by hypoxia, its natural defense mechanisms weaken, making it more susceptible to microbial keratitis, a severe and potentially sight-threatening corneal infection or ulcer. This elevated risk is why adhering to the prescribed removal schedule is fundamental to maintaining eye health with standard monthly lenses.
Extended Wear vs. Monthly Lenses: The Difference
Some lenses are approved for overnight wear, but these are a distinct category from standard monthly lenses. These specialized products are known as Extended Wear (EW) or Continuous Wear (CW) lenses. The key difference lies in the material science and the oxygen permeability of the lens.
Extended wear lenses are manufactured using advanced silicone hydrogel materials, which are engineered to allow a significantly higher volume of oxygen to pass through to the cornea. This high permeability is required to meet the eye’s minimum oxygen requirement even when the eyelid is closed. This design attempts to mitigate the risk of hypoxia during approved periods of overnight wear, which can range from six nights up to a full 30 days, depending on the specific lens and manufacturer approval.
It is important to note that a lens being a “monthly” replacement does not automatically mean it is approved for extended wear. Only lenses explicitly labeled for EW or CW and prescribed by an eye care professional should ever be worn during sleep. Furthermore, even with these highly permeable materials, the risk of infection remains statistically higher than with lenses removed every night. Therefore, professional guidance and monitoring are required before attempting any form of overnight contact lens wear.
Immediate Steps After Accidental Overnight Wear
If you wake up having accidentally slept in your standard monthly lenses, the immediate steps you take can help mitigate potential damage. Resist the urge to remove the lens immediately if your eye feels dry, irritated, or the lens feels stuck. The lens may have adhered to the dried-out corneal surface, and immediate removal could cause a superficial abrasion.
Instead, wait 10 to 20 minutes to allow your eye to naturally produce tears to rehydrate the lens and the corneal surface. Applying a few drops of preservative-free saline solution or rewetting drops approved for contact lenses can speed up this rehydration process. Once the lens moves freely on the eye, gently remove it and discard it immediately, as its integrity and cleanliness are compromised.
After removal, wear your glasses for a full 24 hours to give the cornea time to recover from the temporary stress and oxygen deprivation. Monitor your eyes closely for any persistent symptoms, such as redness, noticeable pain, unusual sensitivity to light, or any change in vision. If any of these symptoms continue after the lens has been out for several hours, seek immediate care from an eye care professional, as these could be signs of a developing infection.