<b>By Mark S. Siegel</b>

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, it’s not a good idea.

When you sleep with your contact lenses in, you’re depriving your corneas of oxygen. This is analogous to wearing a plastic bag over your head when you sleep which is 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 inside the eye 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. 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. The end result is an oxygen-starved cornea, which becomes more susceptible to infection.

Bacteria or parasites can infect any microscopic abrasions of the cornea, which can be caused by contact with the back surface of the contact lenses. These bacterial microorganisms are part of our normal eyelid flora or can be introduced 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), 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 localized infections of the cornea, may cause permanent scarring resulting in loss of vision or even blindness.

In fact, a 2012 study in the journal <i>Ophthalmology</i> showed that the risk for keratitis — inflammation of the cornea — increased 6.5 times with just occasional overnight lens use among people who used contact lenses intended for removal at the end of the day.

While there are some contact lenses that have been FDA-approved for “extended wear,” meaning you can wear them for multiple days at a time, the FDA still recommends people using these lenses remove them and not wear them overnight at least one time a week. However, it’s simply not a good idea to wear these lenses overnight, if you can help it, because there is still an increased risk for infection.

Moreover, multiple studies have shown that people who wear extended-wear lenses (soft hydrogel lenses) have a 10 to 15 times higher risk of developing ulcerative keratitis, compared with daily-wear contact lens users. Overnight wear, regardless of contact lens type, increases the likelihood of corneal infection, which may result in permanent vision loss or even blindness and should be avoided.
<div></div>