Late at night, you cradle your smartphone in your palm and use it before you go to sleep. Although the lights are out, the glaring screen is bright enough for your eyes to see whatever it is you're scrolling through or reading.

Unfortunately, research suggests that the habit of using your smartphone in the dark while lying in bed may induce a negative albeit relatively harmless effect. Doing so may cause a condition called "transient smartphone blindness" or temporary vision loss.

What You Need To Know About Transient Smartphone Blindness

As reported by Tech Times, a previous study described how two women suffered transient smartphone blindness for months after regularly using their smartphones in the dark.

The first woman, a 22-year-old from England, had thought that she was losing her vision in one eye. Although she could see fine out of her left eye, her right eye somehow did not work on some nights. This initially happened to her about twice or thrice every week, and then it occurred every night.

When she visited her doctor, her vision appeared normal. Her brain scans also did not show anything unusual, but the disturbing pattern continued.

Another woman, who was in her 40s, also complained about the same thing. On some days, the woman would lose her vision for about 20 minutes. It was so bothersome that she was rushed to the emergency room.

Loss of vision in one eye is known to be an indicator of small stroke, and may also be a sign of a compressed optic nerve. This is why the second patient was put on blood thinners, while the first patient received a brain scan.

But instead of being diagnosed with these two conditions, doctors say both women actually suffered transient smartphone blindness.

Ophthalmologist Omar Mahroo, the lead author of the paper describing the cases, says both of the patients often looked at their smartphones in the dark while lying in bed. They just happened to have one eye covered when doing so.

Fortunately, in both cases, nothing was going wrong, Mahroo says. The temporary vision loss happens because one retina was adapted to the light, while the other to dark.

The retina can adapt to various light levels and reduce its sensitivity better than any camera can. For instance, when you are at the beach in broad daylight, you can still see well. At nighttime on a clear sky, the retina can also adjust to the dim points of light.

Mahroo tested their hypothesis on the patients and themselves. Both patients viewed the smartphone with just the left eye, and then just the right eye on separate tests. The eye that went "temporarily blind" was always the one that looked at the bright screen.

Meanwhile, the researchers went in a dark room, covered one of their eyes, used the smartphone for 20 minutes and then turned off the screen.

"It did actually feel quite strange," Mahroo says of his self-experiment. "It would be very alarming if you didn't know what was going on."

How To Prevent Temporary Vision Loss Due To Smartphone Use

So how can you prevent transient smartphone blindness? Researchers say they have yet to understand the long-term ill effects of using your smartphone in a dark room with one eye closed, but using it with both eyes is a simple solution.

Furthermore, previous studies have shown that the blue light from screens may not be damaging to the eyes, although it may affect the body's circadian rhythm. To alleviate this problem, smartphone companies have released new features that could help users cut back on these harmful wavelengths. Perhaps, it's like hitting two birds with one stone — if you reduce the brightness of your screen, the effect may not be as severe. This, however, has yet to be proven.

Photo: Andy Rennie | Flickr

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