This might cause you to think twice before checking your email from bed.
A team of London-based researchers has come across two separate cases where women reported temporary blindness — both times in their right eye — on many occasions over the course of several months.
The condition, called "transient monocular visual loss," appears to have been caused by the women using their smartphones in the dark, according to a study published Thursday in The New England Journal of Medicine. And it could be happening to more people.
In both cases studied by the researchers, the patients reported the same behavior before the blindness occurred: They were staring at their phones while lying on their left side in bed.
The longest the blindness lasted was about 15 minutes.
Both women were right handed, and were therefore using that hand to hold their device. In each case, the right eye was adapting to the bright light from the screen, while the left eye was often covered by the pillow. Once the women put their phones down, their right eye, after it had adapted to the screen, was temporarily blinded until it had time to adjust and match the other.
Once doctors told the women to look at their phones with both eyes while in the dark, their temporary blindness disappeared. To substantiate the theory that the problem could be solved by using both eyes, the research team ran a small experiment where they sent subjects into a dark room and recreated the conditions. They achieved the same effect.
"People frequently use smartphones while lying down, when one eye can be inadvertently covered. Smartphones are now used nearly around the clock, and manufacturers are producing screens with increased brightness," the study said.
"Hence, presentations such as we describe are likely to become more frequent. Our cases show that detailed history taking and an understanding of retinal physiology can reassure both patient and doctor and can avoid unnecessary anxiety and costly investigations."
The researchers were from City University, King's College, the National Hospital for Neurology and Neurosurgery and Moorfields Eye Hospital, all in London.