Eyesight is a gift that cannot be taken for granted. Losing some or all means a decline in quality of life and a struggle to adapt. It is a mystery, then, why so many parents allow and even encourage their children to abuse what is perhaps their most important sense by letting them sit for hours in front of computer and television screens.

They should, instead, be advocating a balance, ensuring that some time is spent on outdoor activities.

Medical research unequivocally points to increased use of screen-based devices as being behind a global increase in visual problems. Many people who spend prolonged time using computers or playing video games develop myopia, a permanent condition in which distance sight is blurred and near vision clear. It is especially prevalent in Hong Kong, where children are pressured to do extra school work to get higher marks. That was borne out by an online study by Chinese University and the Project Vision Charitable Foundation, which found 43.1 per cent of 1,965 primary students had the affliction, a 7 per cent increase from a decade ago. There was a rise in the percentage with high myopia, from 1.3 to 2.1.