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.
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.
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.
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.
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.