I share your concern about the way your granddaughter was using the phone to watch video. I have seen this also, children using smartphones for lengthy periods, scrolling social media or watching videos. There is no question that this will strain their eyes. They keep going because they are interested in the content, or bored with things around them.

These screens started with computers several decades ago. The black monitor screen with green letters and cursor was replaced with white screen and multicolour pages. When we spend hours with the eyes focused on the monitor, problem is inevitable. People have complained of blurred vision, pain in the eyes, dry eyes, and headaches. This digital eye strain has also been called Computer Vision Syndrome.

It has been shown that when we work with screens, our eyes are not blinking as frequently as they should. Blinking puts a layer of tear on the conjunctiva, the outermost layer of cells that protects the front part of our eyes. This thin layer of tear provides moisture to the conjunctiva and keeps it healthy. When it dries, our eyes get irritated.

Our eyes can focus on things both close and far. This is done by a group of small muscles inside the eye that changes the thickness of our lens; there is one lens inside each eye. When we keep focusing on any screen, these muscles have to keep adjusting to focus on words and other items on the screen. Over time, these muscles get tired; this is the cause of eye strain many experience after using screen for a while.

There is a 20-20-20 rule: stop focus on screen every 20 minutes, look at something at least 20 feet away for 20 seconds, and blink twenty times. Another suggestion is to take a ten-minute break after every hour of screen use, either for work or for entertainment. This allows the eye muscles to relax and reduce eye strain, as well as keeping the conjunctiva moist.

Other strategies include keeping the screen at least an arm’s length from the eyes, and keep the surrounding dim. If the surrounding is bright, the screen naturally gets brighter; this will strain the eyes more. Move the screen so that light doesn’t shine directly on the screen.

The pandemic has forced children to attend classes online, staring at screens even more. Research has also shown that children have more screen time for entertainment during the pandemic because of isolation. It is even more important for parents to find other activities that their children enjoy, so that they are not using screens all the time.

Smartphones have smaller screens than computer monitors and tablets. It is natural for them to hold these closer, leading to more eye strain than larger screens. In the last few decades, the number of North American children with near-sightedness (myopia) have doubled. In many parts of Asia, the vast majority of young people have myopia. This is partly due to genetics, and partly due to increased indoor activities for education as well as entertainment. Outdoor activities are important for children’s normal eye development.

Children should have vision test once a year. They cannot tell when things are blurry; they assume it is normal. Vision test can detect myopia and other issues early, and prevent deterioration.

Finally, it is important to stop all screens an hour before bedtime, they can affect sleep. It is better for children to read a book in bed instead of using screens. I also recommend parents remove all electronics, including TV, videogame, tablet, and phone, from children’s bedroom at night. It is better to get an alarm clock instead of using the alarm function of the phone.