Nearsightedness, also known as short-sightedness, has seen a staggering increase in the last few decades. There is mounting evidence that children are now spending most of their day in relatively dimly lit classrooms. The same applies to homeschooling facilities and distance learning during the pandemic lockdowns.
Indoor lighting of offices and schools only measures around 300 lux and the average home even less, while outdoor light intensity can measure 50,000 lux.
Just three generations ago, people were exposed to an average of 10 hours of daylight every day. Today’s children – and the rest of us – rely on relatively dim lights for most of our waking hours. This can have serious health consequences.
The reduction in daily light exposure over the years compared to previous generations coincides with the increasing prevalence of myopia. The COVID-19 pandemic has kept school-age children confined indoors and focused on screens, further accelerating the global trend of deteriorating eyesight. In contrast, increasing time spent outdoors decreases a child’s likelihood of becoming myopic.
Myopia typically begins during elementary school, an age when children first need glasses. In this vulnerable population, the growing eye overextends along its anterior-posterior axis. It is not possible to make the eye smaller, so corrective glasses or contact lenses are required. Laser surgery is sometimes possible.
An elongated myopic eye is so distorted that light is focused just in front of the retina. Fortunately, regular exposure to outdoor daylight in excess of 10,000 lux regulates the growth of children’s eyes. More time on the playground could also counter another problem in the rich world: childhood obesity.
Genetics play a role in who develops myopia. A child with two myopic parents has a 60% chance of also being myopic, while spending just two hours a day outdoors effectively neutralizes this genetic risk. How does this work? Bright sunlight stimulates the release of dopamine from a class of specialized retinal cells not involved in vision. These then trigger a cascade of chemical signals that delay the stretching of the eyeball.
In the 1960s, myopia was uncommon in East Asia. Now it’s ubiquitous. In Hong Kong, Singapore and Taipei, more than 80% of school children are now myopic. In the USA, a study from California put the rate at 59% for 17 to 19 year olds. Previous In the 1980’s, the Asian military recognized the major problem that more and more conscripts needed glasses to focus on distant targets.
A 1983 study confirmed that 70% of Taiwanese high school seniors needed glasses to aim properly. The latest rate in Seoul is 97%. Why such high rates in Asia? Its cultural emphasis on education results in long school days and little time for sunshine. After-school tutoring can last long after the sun goes down.
Human experiments support these observations. In a 2020 Taiwanese study, elementary school students participated in a program where they spent two hours a day outdoors. Evidence from Taiwan shows that giving elementary school children more time outdoors reduces the number of students who develop myopia.
Rates of myopia steadily declined between 2010 and 2015, reversing decades of rising rates. Outdoor exposure is around 10,000 lux, while indoor levels rarely exceed 1,000 lux. Sunlight in the tropics can exceed 100,000.
Myopia is hardly benign. Glasses and contact lenses are a lifelong and expensive inconvenience. In poor countries, parents simply cannot afford them. Laser corneal surgery, marketed as Lasik and other brands, is also expensive and doesn’t always correct vision properly. The main concern, however, is that severe myopia predisposes a myopic person to other eye diseases in middle age, some of which can result in untreatable vision loss, such as: B. Macular degeneration.
Myopia is typically viewed as the bane of the bookworm. The more you participate in after-class activities, the more likely you are to be myopic. Education is obviously a proxy for something else: daylight. Studies in California and Sydney, Australia found that spending time outdoors was strongly associated with a lower risk of myopia. The activity didn’t matter – hiking, exercising, picnicking – just being outdoors was the key.
The daylight hypothesis is confirmed by animal experiments in which the light conditions can be carefully controlled: darkness reliably produces short-sighted animals. And how can bright/adequate light unfold its magic or effect? Via dopamine, which is found in the retina and helps regulate the growth rate of the eyeball. Too little and it gets too long to focus properly.