Most contact lenses are designed for daily wear, requiring removal and cleaning every night. Advancements in material science have created a specific category of lenses approved for continuous wear, allowing individuals to keep them in overnight and for extended periods. These specialized lenses offer convenience but require a specific prescription from a licensed eye care professional. Safely sleeping in contacts depends entirely on the lens material’s capacity to allow oxygen to reach the eye, a physiological requirement that standard lenses cannot meet. Wearing any lens overnight without medical guidance significantly increases the risk of serious eye health complications.
Defining Continuous and Extended Wear Lenses
Lenses approved for overnight use are categorized as Extended Wear (EW) lenses. This term describes lenses approved for continuous use longer than 24 hours, typically up to seven days. Continuous Wear (CW) is often used interchangeably but specifically refers to lenses approved for the maximum duration of continuous use, which can be up to 30 nights.
The permissible wearing schedule is determined by the lens material’s characteristics and regulatory approval. The exact duration is a maximum limit set by the manufacturer and adjusted by the prescribing eye care professional based on the individual’s eye health and tolerance. Even lenses approved for 30-day wear may be prescribed for a shorter schedule, such as 7 or 14 days, to ensure optimal eye safety.
The Technology Behind Overnight Contact Use
The core difference allowing a lens to be worn overnight is its dramatically increased oxygen permeability. This addresses the eye’s need for constant oxygen supply. When eyes are open, the cornea receives oxygen directly from the air. During sleep, when eyelids are closed, the cornea relies on oxygen from the blood vessels in the inner eyelid. A standard lens would severely block this limited flow, causing corneal hypoxia.
The solution is the use of Silicone Hydrogel (SiHy) materials, developed specifically to enhance oxygen transmission. Silicone is highly permeable, allowing significantly more gas to pass through the lens than older, traditional hydrogel materials. This capability is quantified using the oxygen transmissibility value, known as Dk/t, where ‘Dk’ is the oxygen permeability and ‘t’ is the lens thickness.
To be considered safe for overnight wear, a lens must achieve a minimum Dk/t value that prevents corneal swelling and hypoxia. Research indicates that preventing oxygen deprivation during sleep requires a Dk/t value generally ranging between 87 and 125 x 10^-9. Older hydrogel lenses often have a Dk/t value in the 20 to 30 range, which is why sleeping in them is discouraged. The high Dk/t of SiHy lenses ensures the cornea receives sufficient oxygen even when the eyelids are closed, preventing damage.
Essential Safety Protocols for Extended Wear
Using extended wear lenses requires strict adherence to guidelines to mitigate risks. The most fundamental safety measure is following the exact wearing schedule prescribed by your eye care professional. Wearing the lens past its recommended date allows protein deposits and bacteria to accumulate, significantly increasing the chance of infection.
Water exposure is an absolute contraindication, especially for extended wear lenses. It is imperative to avoid showering, swimming, or using hot tubs while wearing them. Water contains microorganisms, such as Acanthamoeba, which can become trapped and lead to severe, vision-threatening infections.
Although designed for continuous wear, these lenses still require a mandatory break period, often one night per week for 30-day lenses. During this break, the lenses must be removed, cleaned, and disinfected using fresh contact lens solution, not tap water or saliva. This routine cleaning removes accumulated debris and bio-deposits, maintaining lens integrity and preventing pathogen buildup.
Recognizing Signs of Eye Complications
Despite advanced materials, extended wear carries a higher risk of complications than daily wear. It is important to recognize early signs of a problem. If irritation, discomfort, or a change in vision occurs, the lens must be removed immediately, as ignoring minor symptoms allows complications to progress rapidly.
These signs can indicate issues such as corneal inflammation (keratitis) or a serious corneal ulcer. Should any symptoms manifest, the lenses must be taken out without delay, and the eye care professional should be contacted immediately for an urgent evaluation.
Common Symptoms of Complications
Key symptoms to watch for include:
- Persistent redness
- Noticeable eye pain
- Excessive tearing
- Foreign body sensation
- Sensitivity to light
- Sudden, unexplained blurring of vision