A medical journal has reported that two women have experienced "transient smartphone blindness" after checking their phones in the dark.

For several months, the women reportedly experienced vision loss for up to 15 minutes at a time, and a group of London eye specalists have attributed it to their habit of checking their smartphones with only one eye open in the dark.

"I simply asked them, 'What exactly were you doing when this happened?'" Gordon Plant of Moorfield's Eye Hospital in London told Maria Cheng from the Associated Press.

The women, aged 22 and 40, had undergone a series of inconclusive medical tests, including MRI scans and cardiovascular examinations, before Plant determined that they'd both regularly checked their smartphones in the exact same way.

Before going to sleep and just after waking up, the women would lie on their side, and open the eye closest to the ceiling to check their smartphones. The eye closest to the mattress remained closed on the pillow.

Several minutes after they did this, they'd experience temporary vision loss in the eye they used to check their smartphones. At first, this would happen two or three times a week, but it soon progressed to being a daily occurrence.

Plant and his colleagues hypothesise that the temporary blindness in the 'phone eye' was being caused by the uneven adjustment to light between it and the pillow eye.

"The retina is pretty amazing because it can adapt to lots of different light levels, probably better than any camera," he told Rae Ellen Bichel at NPR. "It can reduce its sensitivity, so that when you're on the beach or in the bright snow you can still see relatively well."

When light hits the retina, it causes the rod-shaped photoreceptor cells inside to change shape. This allows the light signal to be converted into electrical impulses, and these are transmitted to the brain for processing via nerve fibres.

This whole process can take 40 minutes to reset after exposure to bright light, says Bichel, after which our eyes can let us see in the dark again.

So what happens when one eye has adapted to light - a lot of it - by looking at a smartphone screen, and the other is still adapted to darkness? A little thing called differential bleaching of photopigment, say the researchers, which basically tricks the phone eye into thinking it's actually gone blind.

"We hypothesised that the symptoms were due to differential bleaching of photopigment, with the viewing eye becoming light-adapted while the eye blocked by the pillow was becoming dark-adapted," Plant and colleagues report in the New England Journal of Medicine.

"Subsequently, with both eyes uncovered in the dark, the light-adapted eye was perceived to be 'blind'. The discrepancy lasted several minutes, reflecting the time course of scotopic recovery after a bleach."

The thinking is that when one eye is exposed to a crapload of smartphone brightness and another to darkness, it could mess with their ability to calibrate once they're both open at the same time.

This form of temporary blindness is harmless, and of course avoidable if you just use both eyes to check your smartphone in bed. 

And not everyone will experience it if they check their phone in the same way. The fact that it's only been reported in two people suggests that it's a pretty rare response to the behaviour - if the two are even linked at all. Right now, we're looking at an hypothesis based on just two cases, so we need more evidence to know for sure that this is what's really going on.

"Rahul Khurana, a spokesman for the American Academy of Ophthalmology, called it a fascinating hypothesis, but said two cases weren't enough to prove that one-eyed smartphone use in the dark caused the problem," the Associated Press reports. "He also doubted whether many smartphone users would experience the phenomenon."

So until scientists have this one figured out, give your eyes a break and use both to check your smartphone in the dark, and if you do experience temporary blindness in one eye, it could be a mini-stroke, so get to a doctor immediately.

Or, you know, just don't check your smartphone in bed at all, because while the jury's still out on smartphone blindness, it's becoming pretty clear that screens in bed = very bad results for your health: