Med thumb contact lens

If you’re among the more than 30 million American adults who wear contact lenses, there’s a good chance you’ve fallen asleep with those little plastic cylinders still suctioned to your corneas. Maybe you passed out during a Netflix binge, or maybe you ran out of saline. Maybe you just got drunk and forgot. Usually, it’s a harmless mistake.

Except when it’s not.

Sleeping with your contacts is playing eye-care roulette, explains Dr. Mark Eltis, an Ontario-based optometrist and clinical professor who focuses on eye disease. Though most people who don’t remove their lenses before bed will wake up without pain or pus, a small percentage will develop microbial keratitis, an unsavory and potentially blinding bacterial infection that can ransack eyes in just one night. Each year, microbial keratitis affects at least 30,000 people in the U.S.

Why is sleeping in contacts so bad?

Eye-care experts aren’t quite sure. For years, doctors believed that keratitis developed because closed (sleeping) eyes blocked oxygen from reaching the corneas. Though the original contact lenses were hard, soft lenses hit the market in the 1970s and quickly took over. Somewhat counterintuitively, soft lenses let less oxygen pass through. Without oxygen, eyes become dry and infection-prone.

Or that was the thought. The oxygen theory started to fall apart about 15 years ago, when continuous-wear lenses became all the rage and, shortly thereafter, caused all the infections.

But doesn’t “continuous wear” mean wearing continuously?

Continuous-wear lenses are soft, silicone-based lenses with a tremendously high oxygen content. In the late 90s, manufacturers touted continuous-wear as a 24/7 lens, and doctors prescribed them in droves.

Unfortunately, these patients suffered just as much keratitis from sleeping with their continuous-wear lenses. Though the FDA never pulled continuous-wear from the shelves, cautious doctors stopped prescribing them for overnight use.

As for figuring out the root cause of keratitis, it was back to the drawing board.

Experts came up with a few new theories, but Dr. Eltis says there’s no consensus yet. Some research suggests that our immune systems take a break when we’re sleeping, thus increasing susceptibility to infection.

Sometimes I run out of contact lens solution. What then?

Don’t run out. Or, carry a spare pair of lenses in your purse or messenger bag.

If that’s not an option, Dr. Eltis recommends daily disposable lenses for people — particularly young adults — who make game-time decisions to sleep away from home. It’s better to throw out your lenses than to sleep in them.

The obvious alternative, and one we’ve all improvised at one time, is using plain water for storage. This is no better than sleeping in them, says Dr. Eltis. (He declined to say which terrible idea is less terrible.) Storing your contacts in water can actually cause a different, non-bacterial type of keratitis that tends to do less immediate damage, but is also harder to diagnose and treat.

Keratitis can develop in a single night, and may result in vision loss.

What’s the deal with “nighttime-only lenses”?

They’re in a different ball park. Nighttime lenses perform an entirely distinct function. People with mild prescriptions can wear them at night, and only at night, to reshape their corneas and temporarily improve their vision. Then, during the day, they can see without glasses or contacts.

Nighttime lenses, are more of a compelling idea than a useful product, says Dr. Eltis. While they’re designed to admit more oxygen, nighttime lenses still can and do lead to occasional cases of keratitis.

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Why you should never, ever sleep in contacts  

Thirty million Americans pop contact lenses in and out of their eyes every day. Improved sight, however, comes with risks, including heightened susceptibility to infection. Lens wearers are considerably more likely to develop such savory conditions as conjuctivitis (pink eye) and bacterial keratitis, a potentially blinding infection that sends thousands to the eye doctor every year. The precise role that contacts play in breeding infection isn't well-understood. A new study from NYU's Langone Medical Center, however, explores the ways in which lenses alter the eye microbiome, the community of microorganisms that live in and around your peepers. As it turns out, there are some potentially meaningful differences between the bacteria lurking behind the eyelids of lens -and-non-lens-wearers. (Yum) 

With contact lenses comes great eye-care responsibility, and passing out without removing contacts tops the list of mortal lens-wearing sins. Why? In addition to increasing one's chance of waking up to goo-sealed lids, overnight use puts people at risk of getting the above-mentioned condition, keratitis. The bacterial infection is difficult to treat because it causes searing pain (and residual ocular scarring) without visible symptoms. 

Given that contact lens use is among the highest risk factors for keratitis, researchers believe that lenses may invite infection by giving pathogens something to grip onto.

In general, lens wearers are far more likely to get keratitis, among other corneal infections, than members of the lens-less population. And overnight use exponentially raises that risk, but the keratitis-contact link has long thrown eye-health experts for a loop. For a long time, oxygen deprivation was the lead culprit, but the rise of continous-wear contacts in the late '90s largely put the theory to bed, as the popularity of breathable lenses (which let more air pass through) did not coincide with less keratitis. In fact, infection rates climbed. Another, less-outdated belief implicates immune-system function, positing that the dozing, contact-encased eyeball is such fertile infection territory because immunicological defenses power down at night. These days, ophthalmologists and microbiologists are zeroing in on the eye microbiome.

In recent years, scientists have invested more time and money into exploring the the human microbiome. Efforts to map and make sense of the microbiota populating our bodies, however, have primarily focused on five sites: the gut, mouth, nose, skin and urinary tract, as The Scientist reported in 2014. By contrast, the bacteria that cling to the conjuctiva, the mucous membrane on the surface of the eye, have been largely neglected. The oversight may be a function of practicality, as many known eye bacteria are barely visible and thus tricky to culture.

But, the limited body of existing research also highlights the importance of excavating eye bacteria more thoroughly. Keratitis-infected eyes harbor fewer types of pathogen-fighting bacteria than healthy eyes, researchers have found. Given that contact lens use is among the highest risk factors for keratitis, researchers believe that lenses may invite infection by giving pathogens something to old onto. The underlying theory here is called "colonization resistence," which says that microbiota protect the body against foreign bacteria, and that wearing contacts could throw the eye ecosystem out of whack.

The underlying theory here is called "colonization resistence," which says that microbiota protect the body against foreign bacteria, and that wearing contacts could throw the eye ecosystem out of whack.

The recent NYU study reinforces the notion that contacts alter the eye microbiome. "The results indicate that wearing contact lenses alters the microbial structure of the ocular conjunctiva," wrote study authors, "making it more similar to that of the skin microbiota. Further research is needed to determine whether the microbiome structure provides less protection from ocular infections."

The study, published in the March issue of mBio, involved a female-heavy group of 58 volunteers who submitted samples of bacteria from their contact lenses, undereye skin and conjunctivas. Researchers additionally collected bi-weekly samples from 20 of the participants over a six-week period. Here's what they found:

  • Across both groups, eye bacteria "had a higher proportion of hand-like bacteria than of face-like bacteria." But, overall, eye bacteria was more diverse than skin bacteria. Eyes rivaled the mouth in diversity, which study authors deemed "remarkable" given the antimicrobial impact of tears.
  • The eye microbiome of lens wearers was more "skin-like" in composition than that of non-lens wearers (based on comparisons between conjuctiva and undereye samples).
  • In non-lens wearers, gender had some influence on composition of microbiota, but not in lens-wearers.
  • The type and amount of various bacterial strains and families differed considerably between lens-wearers and non-leans wearers. More research, study authors wrote, is needed to determine which bacteria invite infection in lens-and-non-lens wearers. But, the the surface of lens-wearers' eyes harbored an abundance of bacteria that "are considered to be opportunistic pathogens" in common eye infections including keratitis, conjuctivitis and endophthalmitis.

The results reinforce the role of lenses in shaping the eye microbiome, but it remains unclear whether contacts primarily change the eye-environment through finger-on-cornea contamination or "if contact lenses exert selective pressures on the eye bacterial community in favor of skin bacteria." 

Whatever the answer, one thing is certain: nothing good comes from running out of contact solution.