Although some types of contact lenses are made to wear for extended periods of time, most conventional lenses are designed for daily wear and must be removed for cleaning and disinfecting every night before you go to sleep. Sleeping in contact lenses affects the blood vessels in the eye and increases the risk of developing corneal infections that can lead to permanent loss of eyesight.
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Types of Lenses
Conventional contact lenses are soft lenses that are designed for long-term use. They are removed and cleaned daily and can be used for up to one year. Planned replacement lenses are soft lenses made to be used for a specific period of time, from one to six months, before they are replaced. Disposable contact lenses are worn for one day, or up to two weeks, depending on the type, then discarded and replaced with new lenses.
If you cannot see clearly through any type of soft contacts, you may be able to wear rigid gas permeable--RGP--lenses. These are stiffer, smaller lenses that are usually removed daily for cleaning and sterilizing and can be used for up to one year. Some RGP lenses are designed to be worn continually, including overnight, for up to one week.
The more often you change your contact lenses, regardless of the style, the healthier it is for your eyes, notes Oregon Health & Science University's Casey Eye Institute. Even though extended-wear lenses are specifically designed to be worn while sleeping, they are not as good for your eyes as daily-wear lenses that are removed every day.
If you have the choice, Casey Eye Institute says, one-day disposables are the healthiest lenses for most people, because you do not put them back in your eye once removed, so the risk of introducing contaminants is much lower than with two-week disposables or conventional lenses of any type.
Contact lenses that are not designed for overnight wear block the flow of oxygen to the cornea. When oxygen is blocked, new blood vessels form in the eye in an attempt to bring in more oxygen. Because these are not normal blood vessels, they can interfere with your vision. Swelling and clouding of the cornea is another possible side effect from leaving daily-wear contact lenses in your eyes when you sleep. These symptoms also interfere with clear vision.
Contact lenses worn when sleeping can cause an ulceration, or open sore, on the cornea, notes the University of Maryland Medical Center. An ulcerated cornea is associated with bacterial infections, such as keratitis. Although the overall incidence is low, the risk of developing one of several forms of infectious keratitis, an eye disease associated with infection from various bacteria, is 80 times higher among contact lens wearers than non-wearers, and highest among those who use extended-wear lenses, according to the Association of Optometric Contact Lens Educators.
A study published in the 2005 issue of the "British Journal of Ophthalmology" confirms that keratitis occurs significantly more often in contact lens wearers who sleep in their lenses than in those who only wear them when awake. The researchers, from the the University of Manchester and the Royal Eye Hospital in Manchester, U.K., recommend that anyone who wants to sleep in contact lenses cut the risk by wearing only silicone hydrogel lenses.