Staring at your mobile phone or laptop could speed up blindness, according to scientists.
A new study by Toledo University in Ohio found that blue light from digital devices triggers the production of a toxic chemical that kills light-sensitive cells in our eyes, according to the Daily Telegraph.
The resulting damage can speed up macular degeneration – a condition that affects the middle part of vision. Around one in seven people over 50 have some signs of the disease and there is no known cure.
Dr Ajith Karunarathne from the University of Toledo said: "We are being exposed to blue light continuously, and the eye's cornea and lens cannot block or reflect it."
Blue light has more energy and a shorter wavelength than other colours which is why it can cause more damage.
The research team said people should avoid using digital devices in the dark because this can dilate pupils and cause more blue light to enter the eyes.
"It's no secret that blue light harms our vision by damaging the eye's retina. Our experiments explain how this happens, and we hope this leads to therapies that slow macular degeneration, such as a new kind of eye drop," he added.
Macular degeneration begins with the death of photoreceptor cells - or light sensitive cells - in the retina. These cells need molecules called retinal to sense light and trigger a cascade of signaling to the brain. Shine blue light on retinal causes them to kill photoreceptor cells.
"You need a continuous supply of retinal molecules if you want to see," Karunarathne said. "Photoreceptors are useless without retinal, which is produced in the eye."
Dr Karunarathne's team is currently measuring light coming from television, mobile phone and tablet screens in the hope of better understanding how eyes respond to everyday blue light exposure.
"If you look at the amount of light coming out of your cell phone, it's not great but it seems tolerable," Dr John Payton, visiting assistant professor in the UT Department of Chemistry and Biochemistry, said.
"Some cell phone companies are adding blue-light filters to the screens, and I think that is a good idea."
To protect your eyes from blue light, Karunarathne advises wearing sunglasses that can filter both UV and blue light outside and avoid looking at smartphones or tablets in the dark.
"By learning more about the mechanisms of blindness in search of a method to intercept toxic reactions caused by the combination of retinal and blue light, we hope to find a way to protect the vision of children growing up in a high-tech world,' Dr Karunarathne said.
The research, published in the journal Scientific Reports, follows recent figures that revealed the average person in the UK spends more than a day a week online using digital devices.
People are on average online for 24 hours a week, twice as long as 10 years ago, with one in five of all adults spending as much as 40 hours a week on the web.
This is partly due to the rise in use by those aged 16 to 24, who average 34.3 hours a week on the internet.
Ofcom, which compiled the report, attributes a large part of the surge in time online to the rise of smartphones, which are now used by 78 per cent of the population compared with just 17 per cent in 2008, the year after the first iPhone was launched.
Britons are now so addicted to them that they check them every 12 minutes.