Extended wear contact lenses offer convenience for vision correction, allowing users to see clearly without the daily routine of removal and cleaning. They are defined by United States Food and Drug Administration (FDA) approval for continuous wear, including sleeping, for a prescribed number of days. These lenses are designed for people who prefer the ease of continuous vision correction, such as those with unpredictable schedules or active lifestyles. Following the maximum designed wear schedule is important for maintaining eye health and avoiding serious complications.
Defining Extended Wear Lenses
Extended Wear (EW) lenses are distinguished from standard Daily Wear (DW) lenses primarily by their material composition and regulatory clearance for overnight use. While DW lenses must be removed before sleep, EW lenses are engineered to remain in the eye for multiple consecutive days and nights. This is possible due to advanced materials, most commonly silicone hydrogel.
The silicone hydrogel material allows a far greater amount of oxygen to pass through the lens to the cornea compared to older hydrogel materials. This increased oxygen flow is necessary to support the eye’s metabolism when the eyelids are closed and the natural air supply is cut off. The term “extended wear” refers to this continuous, multi-day wearing schedule, not simply wearing the lenses for long hours during the day.
The Maximum Designed Wear Schedules
The maximum designed wear schedules for extended wear lenses are defined by the manufacturer and approved by the FDA, reflecting safety limits. These limits generally fall into two main categories based on the lens type and material generation. The first common maximum limit is up to six nights and seven days of continuous wear before removal and cleaning are required.
A more advanced category of extended wear lenses, often made with highly permeable silicone hydrogel, is approved for up to 29 nights and 30 continuous days of wear. This 30-day period represents the absolute maximum time the lens is approved to remain in the eye without removal. While these are the maximum designed times, an eye care professional may prescribe a shorter, more conservative schedule based on an individual’s unique eye health and tear film chemistry.
Oxygen Permeability and Corneal Health
Maximum wear time is directly linked to the cornea’s need for oxygen, which it absorbs from the air. When the eyelid is closed during sleep, the oxygen supply to the cornea drops significantly, even without a contact lens present. Placing a contact lens over the eye acts as a barrier, further reducing the oxygen available to the corneal tissue.
To prevent oxygen deprivation (hypoxia), extended wear lenses must possess a high oxygen transmissibility, quantified by the Dk/t value. Dk represents the oxygen permeability of the lens material, and ‘t’ is the lens thickness; Dk/t measures how much oxygen passes through the lens to the cornea. Historically, research suggested a Dk/t value of approximately 87 was necessary to prevent significant corneal swelling during overnight wear.
Modern silicone hydrogel lenses achieve Dk/t values far exceeding this historical benchmark, sometimes reaching 125 to over 140, to ensure adequate oxygen reaches the cornea even when the eyes are closed. Despite these material advancements, the eye still requires periodic breaks to allow the cornea to fully recover its natural physiological state. This is why the FDA and manufacturers mandate a lens-free period following the maximum continuous wear cycle.
Health Risks of Exceeding Wear Limits
Exceeding the maximum designed wear limits increases the risk of serious ophthalmic complications. One of the most severe risks is microbial keratitis, a painful corneal infection that can lead to scarring and permanent vision impairment. Overwearing provides a warm, moist environment for bacteria and other microorganisms to thrive, especially as deposits build up on the lens surface.
Chronic oxygen deprivation from overwearing can lead to corneal neovascularization, where new blood vessels grow into the normally clear cornea. This attempt by the body to supply the oxygen-starved tissue can impair vision if the vessels grow into the central visual axis. Ignoring the required cleaning and removal schedule also increases the likelihood of sterile inflammation, which is an immune response to lens deposits and debris trapped beneath the lens. These risks are cumulative and increase the longer the maximum wear limit is ignored.