Many smartphone users are guilty of using their smartphone in the dark to scroll through social media feeds, send a last-minute email or check that one last Instagram post before bed.

This seemingly harmless habit, however, could mess with your vision and cause temporary blindness, doctors warn.

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 problem 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 say, 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.