Transient smartphone-induced blindness may become more frequent due to user behaviour, experts say – and understanding the issue can help avoid unnecessary anxiety and investigation.
A group of London eye doctors write in the New England Journal of Medicine that transient monocular vision loss is a common clinical presentation which isn’t always thromboembolic.
They cite two cases: a 22-year-old woman who presented with several months’ history of recurrent impaired vision in her right eye at night; and a 40-year-old woman who presented with a six-month history of recurrent monocular vision impairment on waking. This could last up to 15 minutes.
Both had been investigated for vascular causes, but their results were normal.
“When the patients were seen in our neuro-ophthalmic clinic, detailed history taking revealed that symptoms occurred only after several minutes of viewing a smartphone screen, in the dark, while lying in bed (before going to sleep in the first case and after waking in the second),” the authors write.
“Both patients were asked to experiment and record their symptoms. They reported that the symptoms were always in the eye contralateral to the side on which the patient was lying.
“We hypothesized 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.
“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 authors sought approval for a study from a research ethics committee, and upon approval, investigated by using smartphone screens.
Two of the authors monocularly viewed a smartphone screen at arm’s length, and quantified the time course of recovery of sensitivity in the dark.
“Visual sensitivity was appreciably reduced after smartphone viewing, taking several minutes to recover, and this reduction in sensitivity was measurable at the level of the retina.”
They argue that the way people view their smartphones may be causing the problem.
“Although most people view screens binocularly, people frequently use smartphones while lying down, when one eye can be inadvertently covered,” the authors write.
“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.
“Hence, presentations such as we describe are likely to become more frequent. 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.”