Just when you thought checking your smartphone while lying in bed at night was perfectly harmless, doctors have issued a warning regarding their use: constantly checking social media, sending emails or texts using your smartphone in the dark may cause you to go temporarily blind.

Doctors recently wrote a letter published in the New England Journal of Medicine detailing the history of two women, ages 22 and 40, in which transient monocular vision loss occurred also known as “transient smartphone blindness.”

Both women had complained of having this phenomenon ongoing for months.  The 22-year-old woman experienced recurrent impaired vision in the right eye occurring at night while the 40-year-old woman had a 6-month history of temporary blindness upon waking lasting up to 15 minutes.

Both women underwent extensive testing, including checking vitamin A status, MRI scans, and cardiovascular exams, searching for clues causing this strange occurrence.  All results came back normal.

After exhausting possible explanations for the unusual eye issue, it wasn’t until taking a detailed history of both women where the source of the bizarre symptoms were finally revealed – both women stated the symptoms occurred within minutes after looking at their smartphone screen while lying in bed at night in the dark. 

Each woman was asked to do an experiment recreating the symptoms and recording their findings.  It was discovered that both women reported the symptoms happened when viewing their smartphone with one eye open only while lying on their side in bed while the other eye was covered by a pillow.

Once they stopped looking at their smartphone is when they would notice the inability to see with the eye that had been reading the screen.  The doctors attributed this to the viewing eye becoming light-adapted while the eye blocked by the pillow was becoming dark-adapted.    When both eyes were uncovered in the dark, the viewing eye was perceived to be “blind” which would last for several minutes. 

There has been some doubt voiced by doctors on this odd happening on whether smartphone use at night in the dark is actually experienced that frequently by the vast majority of users.  Also the two cases are not enough to prove that viewing a smartphone with only one eye in the dark caused the problem.

Although unnerving to have happen to a person, this temporary blindness is considered to be harmless.  There’s a very easy solution preventing such an occurrence from happening – when viewing your smartphone screen in the dark at night, turn down the brightness on the smartphone and have both eyes open.