Staring at your smartphone--could mom be right about this?

At some point your mom probably told you, "If you keep staring at that screen, you'll go blind." Physicians in the United Kingdom agree. Don’t look at your smartphone with only one eye open before going to sleep—or you might go blind (temporarily, anyway). This transient loss of vision can be mistaken for a mini-stroke, warned neuro-ophthalmologists.

In a June 23, 2016 letter published in the New England Journal of Medicine, these doctors described two cases in which patients presented at Moorfields Eye Hospital, in London, UK, suffering from sudden monocular vision loss.

In one case, a 40-year-old woman reported a 6-month history of recurrent monocular visual impairment upon waking, with each episode lasting up to 15 minutes. Clinicians tested for a thromboembolic or vascular cause, but her results were normal.

A detailed history-taking in the neuro-ophthalmic clinic eventually revealed that her symptoms only occurred after several minutes of looking at her smartphone while lying in bed in the dark. When the investigators asked the two patients to record their symptoms, both reported that symptoms always occurred in the eye opposite to the side on which they were 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,” the authors wrote. “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.”

Two of the investigators decided to test the effect for themselves. With one eye covered, they each viewed a smartphone screen held at arm’s length. Then they quantified the time required to recover sensitivity in the dark using both psychophysical and electrophysiological methods.

“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,” the investigators reported.

Because people now use smartphones at all hours in all places, and because manufacturers are developing screens with increased brightness, cases like these will become more frequent, the authors warned. However, “detailed history taking and an understanding of retinal physiology can reassure both patient and doctor, and can avoid unnecessary anxiety and costly investigations,” they added.