For two women in the United Kingdom, mysterious vision problems that happened only at night or early in the morning turned out to have a rather innocuous cause: looking at a smartphone in the dark. 
 
 The cases, which are detailed in a new report, show the short-term vision problems that can occur when people look at a bright smartphone screen in a dark room. 
 
 In the first case, a 22-year-old woman told her eye doctor that she had trouble seeing out of her right eye at night while she was in bed. These episodes happened multiple times a week for a year. Each time, she said she could only see the outlines of objects with her right eye, although her vision was fine in her left eye, and in both eyes the following day. An eye exam showed her vision was normal, and she had no signs of a blood clot or other conditions that could cause short-term vision loss, the doctors said. 
 
 In the second case, a 40-year-old woman told doctors that she couldn't see out of one eye when she woke up in the early morning, before sunrise. This vision problem lasted about 15 minutes, and happened on and off for six months, the report said. 
 
 In both cases, doctors later discovered that these vision problems happened only after the women had viewed their smartphone for several minutes, while lying on their side in bed. [5 Odd Ways Your Tech Devices May Injure You] 
 
 The doctors hypothesized that these problems happened because the patients, without realizing it, were looking at their phone with just one eye, with the other eye blocked by a pillow when they were lying down. In this situation, one eye (blocked by the pillow) becomes adapted to the dark, while the other eye (looking at the smartphone) is adapted to the light, the doctors said. When the smartphone is turned off, the light-adapted eye is perceived to be "blind," until it also adjusts to the dark, the doctors said. 
 
 "What the patients are aware of is the differing visual experience between a light-adapted eye … and a dark-adapted eye … at low ambient light levels," the doctors wrote in the report, published today (June 22) in the New England Journal of Medicine. "As they can see well with the dark-adapted eye, it seems to them that they have lost vision in the eye which — a moment ago — was viewing the smartphone normally." 
 
 The patients were asked to experiment looking at their phone with both eyes, and also with each eye individually. The patients said they did not experience symptoms when looking at their phone with both eyes, and if they looked at their phone with one eye, the symptoms were always in the eye that had been viewing the smartphone, the report said. 
 
 The doctors also tried their own experiment, looking at their smartphones with one eye in the dark, and found that their vision was considerably reduced in one eye, and took several minutes to recover. 
 
 With smartphones now used around the clock, and screens increasing in brightness, according to the researchers, doctors will likely see more cases like these in the future, the report said. But by asking patients detailed questions, doctors should now be able to figure out if a smartphone is involved in vision problems. 
 
 "Our cases show that detailed history-taking and an understanding of retinal physiology can reassure both patient and doctor [in these cases], and can avoid unnecessary anxiety and costly investigations," the doctors wrote. 
 
 Original article on Live Science. ||||| CORRECTS MONTH TO JUNE, NOT JULY - This June 21, 2016 photo shows a smartphone held for a photograph in New York. In a letter published Wednesday, June 22, 2016 in the New England Journal of Medicine,... (Associated Press) 
 
 LONDON (AP) — Warning: Looking at your smartphone while lying in bed at night could wreak havoc on your vision. 
 
 Two women went temporarily blind from constantly checking their phones in the dark, say doctors who are now alerting others to the unusual phenomenon. 
 
 The solution: Make sure to use both eyes when looking at your smartphone screen in the dark. 
 
 In Thursday's New England Journal of Medicine, doctors detailed the cases of the two women, ages 22 and 40, who experienced "transient smartphone blindness" for months. 
 
 The women complained of recurring episodes of temporary vision loss for up to 15 minutes. They were subjected to variety of medical exams, MRI scans and heart tests. Yet doctors couldn't find anything wrong with them to explain the problem. 
 
 But minutes after walking into an eye specialist's office, the mystery was solved. 
 
 "I simply asked them, 'What exactly were you doing when this happened?'" recalled Dr. Gordon Plant of Moorfield's Eye Hospital in London. 
 
 He explained that both women typically looked at their smartphones with only one eye while resting on their side in bed in the dark — their other eye was covered by the pillow. 
 
 "So you have one eye adapted to the light because it's looking at the phone and the other eye is adapted to the dark," he said. 
 
 When they put their phone down, they couldn't see with the phone eye. That's because "it's taking many minutes to catch up to the other eye that's adapted to the dark," Plant said. 
 
 He said the temporary blindness was ultimately harmless, and easily avoidable, if people stuck to looking at their smartphones with both eyes. 
 
 One of the women was relieved the short-term blindness didn't signal a more serious problem like an imminent stroke. He said the second woman was more skeptical and kept a rigorous monthslong diary tracking her fleeting vision loss before she finally believed him. But she couldn't stop checking her phone for messages from bed, he said. 
 
 Dr. Rahul Khurana, a spokesman for the American Academy of Ophthalmology, called it a fascinating hypothesis but said two cases weren't enough to prove that one-eyed smartphone use in the dark caused the problem. He also doubted whether many smartphone users would experience the phenomenon. 
 
 Khurana, who acknowledged that he's an avid cellphone user, said that he and his wife tried to recreate the scenario on a recent evening, but had difficulty checking their phones with only one eye. "It was very odd," he said. 
 
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 Online: 
 
 Journal: http://www.nejm.org
– Doctors have identified a new smartphone hazard, albeit an ultimately benign one. They report in the New England Journal of Medicine on the first known cases of "transient smartphone blindness," temporary vision loss that appears to be harmless. For the two UK women identified as suffering from it, the blindness was brought on by using their smartphones while lying on their sides in the dark in such a way that only one eye was viewing the bright screen while the other was blocked by a pillow. This caused one eye to adjust to the darkness while the other was adapted to the brightness. When the smartphone was turned off, "the symptoms were always in the eye contralateral to the side on which the patient was lying"—that is, the dark-adjusted eye responds fine to the now-dark room, but the light-adjusted eye seemed to suffer blindness for a short period. For both women, who were 22 and 40 at the time, the vision loss lasted up to 15 minutes at a time, with occurrences persisting for months, reports Live Science. The AP reports they were subjected to MRIs and other tests before seeing an eye specialist who was able to diagnose them in minutes. "I simply asked them, 'What exactly were you doing when this happened?'" says Dr. Gordon Plant. One of the women, doubtful of the prognosis, started keeping a record of her blindness incidents, which confirmed the link. A rep for the American Academy of Ophthalmology says the sample size is too small to prove Plant's theory, but the AP comes to a simple conclusion: Always look at your phone with both eyes in the dark. (Regular smartphone use is tied to ADHD-like symptoms.)