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To bacteria, the surface of your eye is a hostile place. Every few seconds, the eyelid comes down with tsunami-like force, sweeping most particles and foreign cells away. As if that weren’t enough, microorganisms have to contend with an army of bacteria-killing proteins.

Some bacteria survive in this inhospitable environment — perhaps helping to protect the eye from other invaders. But it turns out that the additional stress of a contact lens on the eyeball might be too much for them.

On Tuesday, researchers at New York University reported in the journal mBio that the bacterial diversity in the eyes of contact-lens wearers looked more like the microbiome of skin than that of the undisturbed eye.


Eye doctors already knew that contact-lens use can cause tiny scratches in the corneal surface, elevating the risk of certain diseases like conjunctivitis and keratitis. Dr. Lisa Park, an ophthalmologist at the NYU School of Medicine, wanted to figure out if the lenses also caused a change in the eye’s bacterial flora.

So she and her colleagues swabbed the eyes of 20 volunteers — nine who wore contact lenses and 11 who didn’t — and then sequenced the genetic material that stuck to the cotton. They found that the mix of bacteria was different in the two groups: species that are often abundant on the skin were more common in the eyes of lens wearers than they were in the eyes of non-lens wearers.


“By putting a foreign body on the surface of the eye, we may be introducing foreign pathogens,” Park said — although it’s unclear, she noted, if this change in bacterial diversity is involved in the eye conditions more common among lens wearers.

Valery Shestopalov, who studies the eye microbiome at the University of Miami, was excited by these results, which provide preliminary evidence that wearing contact lenses alters the unique mix of bacteria on the surface of our eyes.

But he was critical of the way in which the team analyzed their data, saying they found more bacterial diversity than is plausible. To him, this suggested that they didn’t properly take into account the mistakes inherent in the sequencing technology they were using.

Other experts also took issue with the claims that the microbes detected were resident on the eye.

“If you find DNA in an eye, it doesn’t necessarily tell you that there’s a live microbe there. It doesn’t necessarily tell you there was ever live DNA there,” said Suzanne Fleiszig, an optometrist and microbiologist at the University of California, Berkeley.

Because this sequencing technique doesn’t distinguish between living and dead genetic material, she explained, it might simply be picking up on contamination from the finger without showing that these foreign bacteria form stable communities living on the eye.

But all the experts agree about at least one thing: Whether they cause a revolution in your ocular microbiome or not, contact lenses make infections more likely.

As Shestopalov put it, even if you wash your hands very well, the lens is “still very, very, very much contaminated with your skin bacteria.”