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These women experienced so-called "transient smartphone blindness." Each of them occurred while the women were laying down, wrote a team of London-based doctors.
One woman was 22 years old and experienced several months of vision impairment in her right eye at night, but exams came back with normal results. The other woman, a 40-year-old, would go blind in one eye for 15 minutes when she woke up. Her tests also came back normal.
The doctors concluded that the symptoms only occurred after the women spent several minutes looking at their smartphones in the dark while lying in bed. The 22-year-old woman would look at her phone at night, while the 40-year-old looked at hers in the morning.
The symptoms always occurred in the eye that was contralateral to the side they were lying on - so if they were on their left side, it happened in the right eye, and vice versa.
"Although most people view screens binocularly, people frequently use smartphones while lying down, when one eye can be inadvertently covered," the doctors wrote.
The symptoms popped up because the viewing eye would become light-adapted, while the eye that was blocked by the pillow would become dark-adapted. So, when both eyes were uncovered in the dark, the one that had adapted to light would seemingly go "blind" for a few minutes.
"Smartphones are now used nearly around the clock, and manufacturers are producing screens with increased brightness to offset background ambient luminance and thereby allow easy reading. Hence, presentations such as we describe are likely to become more frequent," the case report said.