Science & technology March 2020 | Youth Hong Kong
Short horizons
eyesight: a cause for concern
N
ot long ago, Shanghai’s city government made 80 minutes of outdoor exercise for school children mandatory. Why? A conviction that it will reduce the speed at which they become progressively more short-sighted. The measure is not popular with parents because it reduces studying time, but for the sake of their eyesight, is it enough?
Myopia, also called nearsightedness or short-sightedness, is the most common cause of impaired vision in people under 40. In recent years, its prevalence has been growing at an alarming rate. In 2000, roughly 25% of the world's population was nearsighted. By 2050, roughly half of the people on the planet will be myopic, according to recent research.
What is myopia? Myopia – or short-sightedness – occurs when the eyeball is too long in its axis relative to the focusing power of the cornea and lens of the eye. Light does not focus on the retina as it should, making distant objects appear blurry. Nearsightedness can also be caused by the cornea and/or lens being too curved for the length of the eyeball. In some cases, myopia occurs due to a combination of these factors.
How bad is it? Myopia’s severity is measured in dioptres, the same unit that is used to measure the optical power of glasses and contact lenses. Kindergarten children are defined as myopic when their prescription is -0.6D. Adults officially become myopic at -1D. Specialists in Shanghai say that 20% of the 20-30-year-olds they have studied develop severe myopia at over -8D. This is five times the global average. 40
What’s to blame? l Gene involvement This is controversial since the phenomenon is recent. In the 1960s, only 20% of China’s population was myopic according to clinicians in Shanghai. What else? l Lack of sunlight and outdoor activity Bright sunlight stimulates the release of a retinal transmitter dopamine which blocks axial growth of the eye and inhibits the development of myopia. l Extreme academic pressure Myopic progression slows down in summer when children spend more time out of doors. Australian researchers also found that 29% of the Singapore-based Chinese children became myopic compared to 3% in Sydney. l Too much screen time Staring at a screen for too long when you are young is not good for your eyes. The message is clear. If you have a genetic disposition for myopia, whether you come from this part of the world or whether it runs in your family, get outdoors in the sun more often and leave your books and phone at home.
