If you're a contact lens wearer, chances are you've snoozed with your contacts in at least a time or two. Maybe you only do it once in awhile, when you fall asleep in front of the TV or forget to bring disinfecting solution on an overnight trip. Or maybe it's more of a regular practice, and you leave them in for days (and nights) at a time.
Either way, eye experts say it's not a good idea.
That's because when you sleep with your contact lenses in, you're depriving your corneas of oxygen.
"It's like having a plastic bag over your head when you sleep," says Dr Rebecca Taylor, MD, an ophthalmologist in private practice in Nashville, Tennessee and a spokesperson for the American Academy of Ophthalmology (AAO). "It's not ideal for oxygen exchange."
The cornea receives oxygen from the air when you are awake, but when you are asleep, it gets nourishment and lubrication from tears and a gelatinous fluid called the aqueous humor. If there's a contact lens in your eye when you're sleeping, then "the contact lens acts as a barrier between the closed eyelid and the cornea, and it's fairly tight over the surface of the cornea", Taylor tells HuffPost. When you're awake, the contact lens is actually supposed to move a bit - about a millimeter of movement with every blink - in order to allow the cornea to get oxygen. But when you're sleeping with your contacts in, the contact lens is unable to move because your eyes aren't blinking.
And then there's the issue of infection. Any microscopic abrasions to the cornea - which can be caused by contact with the back surface of the contact lenses - can become infected by bacteria or parasites. These microorganisms can get in our eyes from the contact lenses themselves ("a contact lens can have some bacteria on it because it's not clean or it's been resting on the eyes for so long," Taylor says), or from water, even when it's safe for drinking. A parasite found in water called acanthamoeba, for example, can cause serious eye infections. Corneal ulcers, which are open sores on the outer layer of the cornea, are also a potential risk, Taylor says. (And then of course there's the story of the girl who went blind after she left her contacts in for six months.)
In fact, a 2012 study in the journal Ophthalmology showed that the risk for keratitis - inflammation of the cornea - increased 6.5 times with just occasional overnight lens use among people who used contacts lenses that were meant to be removed at the end of the day.
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