People who lie with one eye closed on the pillow suffer temporary vision loss mistaken for a stroke

Staring at a smartphone in bed can trigger a temporary loss of vision which doctors mistake for a stroke, experts have warned.

Increasing numbers of patients are visiting hospitals complaining of sporadic sight problems in one eye, lasting up to 15 minutes at a time, according to a report by British neurologists.

A&E doctors often mistake these symptoms for a transient ischaemic attack – known as a TIA or mini-stroke - a warning sign that a major stroke is on the way.

But experts from Moorfields Eye Hospital in London have warned the symptoms are usually nothing more than a result of looking at a smartphone in bed.

Many people lie on their side at night, with one eye against the pillow and the other staring at the screen.

While one eye adjusts to the dark, the other eye gets used to the bright light of the high-resolution screen.

But when they roll over and open both their eyes, the eye which has been staring at the screen cannot cope with the darkness of the room.

‘Subsequently, with both eyes uncovered in the dark, the light-adapted eye is perceived to be “blind”,’ said the neurologists, writing in the New England Journal of Medicine.

It usually takes several moments for the eyes to adjust, leading people to believe they are suffering from a severe problem.

The medical team, which also included experts from the National Hospital for Neurology and Neurosurgery and City University London, warned this fleeting loss of vision is too often mistaken for a TIA, leading to ‘unnecessary anxiety and costly investigations’.

 ‘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,’ they said.

‘Hence, presentations such as we describe are likely to become more frequent.’

The experts’ report details two cases in which patients were eventually sent to Moorfields Eye Hospital after brain scans, heart screens and blood tests could find nothing was wrong.

The first, a 22-year-old woman, had suffered dimmed vision nearly every night for a year before she went to the doctor.

‘The ophthalmologist took the history as a bizarre cluster of symptoms of dimmed vision when laying down at night and loss of definition,’ the experts wrote.

‘Her right eye was only able to see the outlines of objects.

‘The entire visual field was affected - she could see no more than vague outlines of objects which were more clearly visible with the contralateral eye.’

Eventually, the doctors realised she looked at her smartphone every night while lying on her side before going to sleep.

And when she tried looking at her phone with both eyes open, the problem disappeared.

The second patient, a 40-year-old woman, would read her phone in bed when she woke up in the morning.

‘She would lie on her left before sunrise, read the news headlines on her smartphone for several minutes and on rising she noted her right eye could not see as well as the left,’ they wrote.

‘She had to wait “many minutes” for it to resolve. Further enquiry revealed the onset of her symptoms coincided with her acquisition of the Apple iPhone 5 smartphone.’

Study author Dr Gordon Plant, a neurologist at Moorfields, said the problem was on the rise.

‘I see patients every two or three months with similar stories,’ he said.

‘In the past we would see this come up if patients lay in bed watching TV, but smartphones are making it much more common because more people are looking at their gadgets last thing at night.’

He stressed that the impact on sight is only temporary - leaving no lasting problems.

But investigating strokes is costing the NHS a fortune in wasted time, and causing severe anxiety to patients.

The problem has been exacerbated by the creation of emergency stroke units, where patients are fast-tracked from A&E straight to a doctor at the merest hint that a stroke has occurred. 

In the past, Dr Plant said, patients would probably see an eye doctor first.

‘It is absolutely critical that when doctors take a history they work out what someone was doing at the time the symptoms occurred,’ he said.

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