Waking up and squinting at your phone in the dark with just one eye can cause temporary blindness, doctors warn.

The New England Journal of Medicine has published a report citing two cases where women suffered ‘transient smartphone blindness’ lasting several months.

The two women, one aged 22 and the other 40, had complained of recurring bouts of temporary blindness lasting up to 15 minutes. The affliction lasted for months.

Both women were given a variety of tests as well as Magnetic Resonance Imaging scans of their brain for doctors to determine what was happening.

Was it an impending stroke? Was it nerve damage?

They found nothing.

So, they asked.

“I simply asked them, ‘What exactly were you doing when this happened?’,” Dr Gordon Plant of Moorfield’s Eye Hospital in London, wrote.

He says both women told him they regularly looked at their smartphones with only one eye — and held a pillow over the other.

“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.

After putting the phone down, they could not see with the eye that had been looking at the phone.

Why?

“It’s taking many minutes to catch up to the other eye that’s adapted to the dark,” Dr Plant said.

Such temporary blindness is harmless, he said.

And there is an easy way to avoid the affliction: Open both your eyes.