Here's why that's way, way better than sleeping in your contacts (unless they're approved by the FDA for overnight use): Your cornea gets its oxygen from the from the air, and when you wear contacts there's an extra barrier, says Laura DiMeglio , OD, an instructor of ophthalmology at Johns Hopkins University. When you're going about your day it's usually no big deal, but when you're asleep, your eyelids are closed and it's even harder for your eyes to breathe. And if your eyes can't breathe, you can get small "breaks" on the surface of your cornea, which let bacteria get inside of your eye and potentially cause an infection, she says. "These infections can create ulcers that, if in the centre of your vision, can result in vision loss, including blindness," Dr. DiMeglio says.