We've all woken up groggy in the morning and looked at our smartphone to check updates from our friends, family and loved ones on social media – and to try and wake ourselves up first thing.
However, this act could carry a greater risk than might be expected, as two doctors have found two women went temporarily blind after doing just this.
They are alerting others to the phenomenon in an effort to raise awareness of the potential dangers involved with smartphones having a mitigating effect on a person's vision.
The two women – aged 22 and 40 – constantly checked their smartphones in the dark and went on to experience a condition described by the doctors as 'transient smartphone blindness' for months afterwards.
Writing their findings in the New England Journal of Medicine, the doctors explained that the women complained of repeated episodes of temporary vision loss for up to 15 minutes. After subjecting the patients to a series of medical exams, as well as heart tests and MRI scans, the doctors could not find anything wrong that would explain the issue.
Dr Gordon Plant of Moorfield's Eye Hospital in London said the mystery was solved minutes after they walked into his specialist office, when he asked what they were doing when the problem happened.
It was revealed that both women usually look at their smartphones with one eye open while resting on their side in bed when it's dark. The other eye is typically covered by the pillow.
“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 remarked.
Because of this, they could not see with the eye that was looking at the phone after they put it down. That's because it was struggling to adjust to the dark and sync up with the other eye, or “taking many minutes to catch up to the other eye that's adapted to the dark”, according to Dr Plant.
This form of temporary blindness was described as ultimately harmless – and therefore not a major health concern. However, it is also easily avoidable if a smartphone is only looked at with both eyes – particularly in low lighting conditions.
One of the patients expressed relief that the symptoms were not an indication of a more severe issue such as an imminent stroke. However, the other patient was more sceptical of the diagnosis and kept a month-long diary tracking her vision until she finally accepted the prognosis. Despite this, she did not stop checking her smartphone for messages while in bed.
Dr Rahul Khurana, a spokesman for the American Academy of Ophthalmology, said the matter is a fascinating one, but that he does not believe the two cases are enough to prove that smartphone use was behind the issue. Doubts were also expressed that many other smartphone users might experience the phenomenon.