Beware of browsing your phone in bed in the dark

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Several scientific studies have confirmed that using bright devices before sleep, especially while lying in bed in a dark room, delays sleep, confuses the biological clock, and impairs alertness the next morning. It may cause some people to have a temporary loss of vision in one eye without this reflecting an organic disease.

This conclusion was based on a clinical trial conducted at the American Brigham and Women's Hospital, and on a scientific thesis that described two cases of two women who visited a clinic specializing in neuro-ophthalmology.

Note that the experiment was not limited to phones, as participants used a light-up tablet, but the researchers pointed out that light-emitting devices include smartphones, computers, and televisions, and that their use extends to the hours before sleep for millions of people.

The experiment included 12 healthy young adults who stayed in a physiological monitoring unit for fourteen days, and read about 4 hours before bed for five consecutive nights from a tablet illuminated at the highest brightness, and then for another five nights from a printed book in dim lighting.

It turned out that reading from the device reduced evening levels of melatonin, the sleep-inducing hormone, by about 55%, while no decrease was recorded with a printed book, and the start of its secretion in the circadian rhythm was delayed by more than an hour and a half, according to what was published in the journal Proceedings of the National Academy of Sciences of the United States.

It took the participants about an additional 10 minutes to fall asleep after reading from the device, as the average was about 26 minutes compared to about 16 minutes with the printed book, and the duration of rapid eye movement sleep decreased from about 121 minutes to about 109 minutes.

Participants reported less sleepiness in the evening, while the next morning they felt more sleepy and took longer to reach the same level of alertness, even though the morning lighting was identical in both cases. There were no differences in total sleep time or sleep efficiency.

The researchers suggested that the short-wave blue light emitted by these devices was one of the factors, as the peak of the light emitted by the device was about 452 nanometers, but they acknowledge that the experiment did not include a device emitting longer wavelength light for comparison, which means that the differences may be due to the intensity of the radiation and not to its spectral composition.

In a different context, the scientific thesis described two cases of two women, aged 22 and 40, who suffered from recurring double vision in one eye, at night in the first case and upon waking up in the second, and the symptom lasted for up to 15 minutes in the second case. The medical tests were normal, and treatment with aspirin began for the second woman, before a detailed medical history revealed that the symptoms did not appear until minutes after looking at the phone screen in the dark while lying down.

The two patients reported that the symptoms always appeared in the eye opposite the side on which they were lying. Doctors explained this by what they called differential bleaching of the photopigment. The eye that looks at the screen adapts to the light, while the eye covered by the pillow remains adapted to the darkness. When the two eyes look together at the darkness, the eye that has adapted to the light appears as if it is blind for minutes, which reflects the course of recovery of night vision.

Two researchers from the team also tested the hypothesis on themselves. Each of them viewed a phone screen with one eye from an arm's length away, and measured the time for recovery of visual sensitivity in the dark, both psychologically and electrically. It turned out that sensitivity decreased significantly and it took minutes to recover, and that the decrease could be measured at the retinal level. The team believed that understanding this mechanism reassures the patient and the doctor and spares them unnecessary anxiety and costly examinations, and expects that these cases will become more common with the almost continuous use of phones and the increase in screen brightness.