We already know dirty contacts cause almost 1 million cases of keratitis, or corneal infections, every year in the United States. Now, a new study published in the journal mBio offers some insights into why. A team of scientists the New York University School of Medicine compared the eye bacteria of folks who do and do not wear contact lenses. They discovered contact lenses recalibrate our ocular conjunctiva (the film that lines the surface of our eyeballs and eyelids) to be more like the bacterial cocktail that sticks on our skin. As a result, the eyes of contact lens wearers contain more strains of bacteria, such as Pseudomonas, Acinetobacter, Methylobacterium and Lactobacillus, that normally reside on our flesh and don't make their way behind our glasses. The study's authors think that might explain the contact lens-keratitis connection, but also say that more research is needed to conclusively prove it. The presence of new bacterial strains isn't necessarily bad news, however. Our skin, guts, and mouths host hordes of healthy bacteria that ward off disease and infections. The same goes for our eyes, according to this study. Scientists have only recently started to investigate the composition and function of the bacteria coating our ocular conjunctiva. For now, your contacts lenses can stay put, since this study didn't determine the long-term health effects of contact lenses on your eye bacteria. “Future studies are needed to determine the role of the microbiome in the increased risk for eye infections in contact lens wearers,” senior study author Maria Dominguez-Bello told Time. For optimal ocular health, the American Academy of Ophthalmology (AAO) stresses "safe handling, storage, and cleaning of your lenses are key steps to reduce your risk of a keratitis infection." Also, watch out if contacts begin causing redness, blurred vision, or discharge, the AAO warns. Those are all signs of infections that could lead to vision loss if left untreated.