Extended wear (EW) contact lenses offer significant convenience by allowing continuous wear, including overnight, often up to 30 days. This modality appeals to individuals with active lifestyles or those who prefer waking up with immediate clear vision. However, this convenience introduces a trade-off involving a statistically higher potential for serious eye health issues compared to lenses removed nightly. The fundamental risk associated with sleeping in any contact lens remains a primary concern for eye care professionals.
Defining Extended Wear Lenses
The ability to wear a contact lens overnight is directly tied to the lens’s oxygen permeability, measured by the Dk/t value. The cornea, which lacks blood vessels, receives its oxygen supply primarily from the air when the eye is open. When the eye is closed, the cornea relies on oxygen from the blood vessels in the inner eyelid, a supply that is naturally restricted.
Standard daily-wear lenses impede this reduced nighttime oxygen flow, which is why they are not approved for sleep. Extended wear lenses are engineered using advanced silicone hydrogel materials that allow approximately five times more oxygen to pass through than traditional hydrogel lenses. This high oxygen transmissibility is necessary to mitigate corneal hypoxia, the oxygen deprivation of the cornea. Research suggests that a minimum Dk/t value of around 87 to 125 is required to avoid corneal swelling during overnight wear. While current EW lenses meet this requirement for most patients, they do not eliminate all the physiological challenges of continuous wear.
Primary Safety Risks of Extended Wear
The most serious hazard associated with extended wear is the significantly increased risk of microbial keratitis (MK), a severe infection of the cornea. Sleeping in any contact lens, even those approved for extended use, is the single greatest risk factor for this sight-threatening condition. Studies show that the risk of developing MK is up to 5.4 to 16 times higher with overnight wear compared to wearing lenses only during waking hours.
This elevated risk is due to factors that occur when the eye is closed and covered by a lens. The lens can trap bacteria and other microorganisms against the corneal surface, and the reduced tear circulation during sleep minimizes the eye’s natural defense mechanism for clearing debris and pathogens. For EW soft lenses, the annual incidence of MK is approximately 20 per 10,000 wearers, compared to a rate of 2 to 4 per 10,000 for daily wear soft lenses.
Even with the high oxygen permeability of modern silicone hydrogel lenses, chronic low-level oxygen deprivation can still lead to long-term physiological changes. One such change is corneal neovascularization, where new, abnormal blood vessels grow into the normally clear cornea in an attempt to supply oxygen. This condition is a sign of chronic hypoxic stress and can permanently compromise vision if the vessels grow into the central visual axis.
Continuous wear also accelerates the buildup of protein and lipid deposits on the lens surface, which can trigger inflammatory responses. This constant irritation can lead to conditions like Giant Papillary Conjunctivitis (GPC), where the inner surface of the eyelid develops large, inflamed bumps. GPC often causes discomfort, itching, and excessive lens movement, necessitating the complete cessation of lens wear until the inflammation resolves.
Essential Guidelines for Safe Use
Users choosing extended wear lenses must adhere to a strict regimen of care and professional supervision to mitigate the associated risks. The first guideline is to rigorously follow the prescribed wearing schedule and never exceed the maximum approved duration. Eye care professionals often recommend a seven-day schedule with at least one night of removal per week to allow the cornea to recover.
Lenses must be removed immediately if any symptoms of irritation, pain, redness, or blurred vision occur, as these are often the first signs of a developing infection or complication. Trying to ignore discomfort can quickly escalate a minor issue into a serious vision-threatening event. A backup pair of glasses should always be readily available for use during these recovery periods.
Proper hygiene is non-negotiable for reducing the risk of microbial contamination:
- Wash and thoroughly dry hands before touching the lenses.
- Use only new, unexpired disinfecting solution.
- Never rinse lenses with tap water or saliva.
- Clean the lens storage case daily and replace it every three months.
Individuals who wear EW lenses require more frequent and thorough professional eye examinations than daily-wear users. These check-ups, often recommended every six months, are necessary to monitor the subtle health of the cornea. An eye care professional can detect early signs of hypoxia, inflammation, or neovascularization before the patient experiences noticeable symptoms.