06/23/2016 03:51 EDT | Updated 06/23/2016 03:59 EDT

Smartphone Use In Bed At Night Blamed For Temporary Blindness

We’re all guilty of it — you’re lying in bed, scrolling through Twitter when you drop your phone on your face. It’s painful and embarrassing, but there’s now another reason to rethink your late-night phone habits.

Two women in the U.K. reported temporary blindness in one eye after staring at their smartphones in bed. According to a study published in The New England Journal of Medicine on Thursday, both women had been experiencing the phenomenon for several months.

After various tests, doctors couldn’t find anything to explain the vision loss, but a specialist from Moorfield’s Eye Hospital in London figured it out by asking one question.

“I simply asked them, ‘What exactly were you doing when this happened?’” Dr. Gordon Plant told The Associated Press.

The women, aged 22 and 40, said they had been looking at their phones with one eye while lying on their sides — and the other eye was shielded by a pillow.

Blindess lasted up to 15 minutes

The 22-year-old said she would lose her vision at night after several minutes of smartphone activity, while the 40-year-old would experience it when she woke up in the morning. The blindness would last for up to 15 minutes.

The study explained that the symptoms were caused by each eye trying to adjust to different lighting. The covered eye adapted to darkness, while the eye looking at the phone adjusted to the bright screen.

When they uncovered both eyes, the light-adapted eye went blind because it couldn’t catch up to the other eye fast enough.

Plant said that the phenomenon, which the researchers are calling “transient smartphone ‘blindness,’” is harmless, which was a relief to one of the women who feared it was signalling something more serious like a stroke.

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