Using your smartphone in the dark could cause temporary blindness, doctors warn

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.

According to a report published in the New England Journal of Medicine, two women in the UK experienced recurring instances of "transient smartphone blindness" – a condition where they went temporarily blind in one eye for up to 15 minutes after looking at their smartphones in the dark.

The first patient, aged 22, complained that she experienced these episodes of temporary blindness in her right eye over several months while using her phone in bed. The second patient, aged 40, said she faced a similar issue intermittently over the past six months while checking the news on her smartphone before sunrise.

A series of MRI scans, heart tests and medical examinations, however, could not explain the mysterious phenomenon in either of the patients.

After visiting a neuro-ophthalmic clinic, both women revealed that the symptoms occurred after several minutes of viewing their smartphone screens while lying in bed in the dark. The doctors soon found that the symptoms occurred because the women usually stared at their smartphones with one eye while the other was covered by a pillow.

While the eye blocked by the pillow becomes adapted to the dark room, the other eye used to view the smartphone becomes adapted to the light. When they stop gazing at their smartphone, the light-adapted eye becomes temporarily "blind" for several minutes until it recovers and adjusts to the dark as well.

"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," the report says. "Subsequently, with both eyes uncovered in the dark, the light-adapted eye was perceived to be 'blind.'"

When the doctors conducted their own experiment with the patients, they found the women did not experience these symptoms when looking at their phones with both eyes. However, if one eye was covered while the other was staring at the smartphone, the symptoms returned.

"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," the doctors wrote. "Our cases show that detailed history taking and an understanding of retinal physiology can reassure both patient and doctor and can avoid unnecessary anxiety and costly investigations."

The temporary blindness, however, is harmless and avoidable if smartphone users continue to use both eyes while gazing at their smartphones, Dr Gordon Plant of Moorfield's Eye Hospital in London and one of the report's authors told AP.

According to Dr Rahul Khurana, a spokesman for the American Academy of Ophthalmology, the hypothesis, while interesting, could not definitively prove that one-eyed smartphone usage did in fact cause the temporary blindness based on two cases alone. He was also doubtful whether a lot of other smartphone users would experience the same symptoms.

Previous studies have also highlighted the negative effects of staring at your smartphone, tablet, computer or TV screen before bed.

According to a study published in the Proceedings of the National Academy of Sciences, the blue glow of gadget screens can reduce the production of melatonin, a hormone that helps induce sleepiness, disrupt circadian rhythms as well as delay and reduce the amount of REM sleep, thus preventing you from getting a restful sleep.