Two poor souls suffered through MRIs, heart scans, and other medical tests to figure out what was causing them to go blind for up to 15 minutes at a time. After discovering that checking their phone in bed was to blame, one woman still couldn’t stop. Such is the power of technology. The women (ages 22 and 40) were understandably very concerned about what seemed like recurring vision loss, according to an article in the New England Journal of Medicine. After the medical tests were inconclusive, they went to an eye doctor who simply asked them where they were when the blindness started. Turns out they were in bed, which doctors determined was the root of the ailment. The problem isn’t caused by being in bed. The issue is that both women checked their phone with one eye on the screen and the other covered by a pillow. Where the phone eye adapts to the light by being less dilated, the pillow eye is more dilated and adapts to the dark. After the phone is switched off, the phone eye takes a while to adjust to the dark and catch up to the pillow eye, causing the feeling of temporary blindness. There wasn’t any true vision loss, but it was an effect similar to how we feel “blind” right when we go into a dark room after being outside. The (obvious) bad news here is that not being able to see is scary, and nearly all of us check our phones in bed. The good news is that “transient smartphone blindness” is avoidable and we can technically continue checking tweets in bed as long as we use both eyes. These two case studies aren’t definitive, and experts tell The Guardian that temporary smartphone blindness is a rare phenomenon. But now we know of at least one more thing that can go wrong with our eyes . And really, even if you don’t go blind, it’s probably best not to check your phone in bed. Nightmode exists for a reason: We really do need to sleep in total darkness . Your texts can wait until morning.