Myopia: The Evidence for Environmental Factors

Centuries ago, dedicated monastic scribes or cloistered seamstresses might have blamed failing eyesight on their particular type of near-focus “close work.” By the late twentieth century, such blame was expanded to include “close leisure,” such as countless hours spent sitting in front of the television, and most recently squinting at high-resolution monitors on everything from gaming consoles to cell phones. However, despite ongoing attempts to tie these close behaviors to the onset of nearsightedness, or myopia, researchers have not come up with convincing results. On the other hand, a rapidly growing body of research on populations in Asia is yielding strong evidence linking diminishing levels of exposure to outdoor light with a prevalence of myopia that is approaching epidemic proportions.1,2,3 “Keep myopia at bay,” chirp colorful screensavers and wallpapers offered by Singapore’s Health Promotion Board. “Go outdoors and play.” The irony of flashing messages on a computer monitor to get children away from that same monitor is not lost on the researchers who have been charting the rise of chronic nearsightedness in the region’s populations. Singapore’s health authorities launched the public awareness campaign in response to a sharp spike in myopia rates among children and young people that was flagged by the country’s military. Military service is compulsory in Singapore, and the eye examinations conducted on incoming conscripts effectively provide a population-wide survey. By the late 1990s, these examinations pointed to a prevalence approaching 80%.4 Comparable findings have been reported in other Asian countries such as Taiwan5 and South Korea.6 Meanwhile, many parts of Asia have undergone rapid economic development, and demanding educational regimes have been implemented over the past two decades to create a highly skilled, dedicated workforce to keep building the momentum of this economic drive.7,8 Not only do children spend most daylight hours in classrooms, they remain equally sequestered at home, either finishing up schoolwork or engaged in leisure activities that keep them glued to one screen or another.7,8,9 “It took me a while to realize how distorted a child’s experience of the world is in China,” says Ian Morgan, an Australian ophthalmology researcher who spends about five months of each year in Guangzhou studying myopia. “In Guangzhou, the climate is hot and sticky for most of the year, and people get outdoors in the evening. But you do not see children of school age, because they are at home doing their homework,” he says. This lifestyle appears to exact a toll on young eyes. Population surveys in Guangzhou, Singapore, and Taiwan point to these areas as hot spots for children becoming myopic earlier, with more of them being more severely myopic.4,5,10,11 But even as the precise factors responsible for the increase are still being debated and explored, a mounting body of evidence cites time spent outdoors as crucial to the healthy development of the eye. Although myopia is becoming more prevalent worldwide, some areas are more affected than others. Surveys in the United States and most especially in Australia, for example, yield prevalence figures for the general population that are consistently much lower than comparable figures in Southeast Asia.12,13 The sharp region-specific disparity also appears to affect primarily the younger generation. Among adult populations around the world, prevalence rates show less variation across countries (although future surveys are expected to show similar disparities in adult rates as today’s youth age). Research drawing on data from the 1999–2004 iterations of the National Health and Nutrition Examination Survey (NHANES) estimates that U.S. myopia prevalence can range from 33.1% across the entire adult population to as little as 25.1% for Mexican Americans.13 By comparison, one study of myopia in Singaporean Chinese, Malay, and Indian adults reported rates of 38.7%, 26.2%, and 28.0%, respectively.12 Myopia may not be as grave a health problem as cancer or heart disease, but there is more at stake than a population saddled with the expense and inconvenience of coping with glasses or contact lenses. Studies suggest the condition may be a risk factor for more serious eye problems including cataract14 and glaucoma,15 although myopia’s relationship to these other problems is still unclear. (On the other hand, myopia is negatively associated with age-related macular degeneration.16) Young people afflicted with the most serious degree of myopia display few other symptoms, but middle-aged individuals with “high” (severe) myopia exhibit many pathologies of the eye.8