Conventional wisdom is that holding a smartphone too close to your face can cause myopia, or nearsightedness. It’s something you may have heard your parents or grandparents warn you about. Now you’ll get a warning from a very different source: Tencent’s video app.

The app will now blur images when kids get their face within 16 inches of the screen, and warns them to move away. For now it’s only available on the iPhone X and newer models, which are equipped with Apple’s TrueDepth cameras -- the same technology that allows Face ID to work.

Why is Tencent doing it now? Last month its shares dived after President Xi Jinping complained about the eye health of Chinese youth.

When a kid leans too close, the screen blurs and a message pops up, saying “Please watch farther away.” (Picture: Tencent via WeChat)

Tencent’s new protective feature might seem like an easy way to appease authorities and parents. But whether it actually helps kids is questionable.

While it’s true that more children in China are wearing glasses these days, the problem might in fact have little to do with how long they spend watching Peppa Pig -- or how closely they stick to the screen.

Studies have shown that a large proportion of people who stare at computers or read books a lot don’t develop myopia. Instead, the key factor might be how much we expose ourselves to sunlight, i.e. hanging outdoors.

Researchers found that young people who get more UVB light are less prone to myopia. Scientists still aren’t sure why, but it seems like getting your kids to walk the dog outside or ride a bike around the block is a good way to protect their eyes. Separately, eating leafy vegetables also helps.

But even if you spend a good amount of time outdoors, it still doesn’t mean you can then play with your smartphone for hours on end. While screen time may not cause permanent eye damage, they do make your eyes temporarily dry and blurry.

To prevent that, the American Academy of Ophthalmology recommends that you sit about an arm’s length from the screen, and take 20-second breaks every 20 minutes.