Outdoor play helps kids see the point
Twelve-year-old Megan Lim does not have much time to play outdoors. The bespectacled girl used to go cycling or rollerblading at least once a week when she was eight, but she stopped after her homework increased dramatically.
With the reduction in outdoor playtime came a corresponding increase in her myopia from 150 degrees to 400 degrees in both eyes today. 'It's too late to do anything about it now, because she's reached puberty and her vision has stabilised,' says her mother, Tang Meng Choo.
It's been known for some time that outdoor play can keep myopia at bay. A Cambridge University study has found that for every hour children spend outdoors each week beyond the norm, their risk of developing myopia falls by 2 per cent. The study, involving 10,000 children and adolescents, found those with myopia spend 3.7 fewer hours outdoors a week on average than children with normal vision.
In an earlier study announced in June, researchers at the University of Sydney hypothesised that lack of exposure to sunlight may be the main factor in myopia. Exposure to sunlight releases retinal dopamine, which inhibits eye growth. This prevents myopia, which develops when the eyeball is too long so that light entering the eye falls in front of the retina instead of directly on it. When this happens, close objects are seen clearly, and objects farther away appear blurred. The study suggested that children should spend two to three hours a day outdoors, as there is 10 times more light outdoors than indoors.
These studies may explain why so many young people in Hong Kong are myopic. The city has one of the highest rates of myopia in the world - three times that of the United States and more than 10 times that of the Middle East. Five per cent of kindergarten-age children and 36 per cent of primary school students need glasses. Sixty per cent of secondary school students have myopia. Among university-age students, the figure rises to 90 per cent.
Although myopic parents are likelier to have myopic children, environmental factors play a bigger role. Hong Kong's dense population, poor air quality, relative lack of play areas and stressful education system combine to keep children indoors for extended periods. As a result, many of them engage in activities such as reading, doing homework, watching television or playing computer games.
'Children tend to hold books too close to their eyes when they read. They also write with their heads too close to the desk. In addition, many spend a lot of time playing video games and tend to hold the consoles too close to their eyes,' says Dr Chng Nai-wee, consultant ophthalmologist with Eagle Eye Centre in Singapore. Such habits - called 'near work' - cause myopia because they force the eye to focus on close objects within half a metre for extended periods. This causes the eye to lengthen gradually, affecting distance vision.
'Although the majority of children in Hong Kong have low to moderate myopia of between -3 to -6 diopters, some have severe myopia of greater than -6 diopters. I have seen patients with more than -20 diopters,' says Dr Dorothy Fan Shu-ping, consultant ophthalmologist at Hong Kong Sanatorium & Hospital. A diopter, expressed in negative numbers for myopia, is the power of the lens needed to correct vision. The higher the number, the stronger the lens. One diopter corresponds to 100 degrees.
Several therapies have been developed to try to correct myopia. These include eye exercise programmes, as well as products such as pinhole glasses, which purport to cure myopia by exercising the eye's muscles. The latter claim has been decried as a myth by the American Optometric Association.
'So far, only the use of atropine eye drops is clinically proven to control or slow myopia progression,' Chng says. Atropine, a naturally occurring substance found in certain plants, relaxes the eye's focal muscles when the person works. A study by the Singapore Eye Research Institute published in 2006 found that a nightly dose of 1 per cent atropine eye drops slowed the progression of low and moderate childhood myopia compared with a placebo treatment.
Ultimately, the best way to keep myopia at bay seems to be simply sending children outdoors to play more often.
'Parents should encourage more outdoor activities for all preschool children at the age of three to four years, especially if they themselves have myopia,' Chng advises. This has the added benefit of encouraging physical fitness, which children in highly urbanised environments such as Hong Kong typically lack.
If going outdoors is not possible, good posture while engaging in near work will also help. 'As we know that near work makes myopia worse, we should encourage children to read and write at a proper distance,' Fan says. The ideal focal distance for reading and writing is 38 to 63cm, and at arm's length for computer viewing.