Nearsightedness and the Indoor Life

Why did myopia increase by 66 percent between the early 1970s and the early 2000s?

Lauren Nelson/flickr

Not too long ago, kids with glasses were the odd ones out, favorite targets of school bullies. But glasses-wearing students are increasingly becoming the norm, with as many as one in four children needing corrective lenses, according to recent studies.

Over the past 15 years, the world has witnessed an explosion of cases of myopia, or nearsightedness. A quarter of the world's population, or 1.6 billion people, now suffer from some form of myopia, according to the Myopia Institute. If unchecked, those numbers are estimated to reach one-third of the world's population by 2020. While myopia has always affected a fraction of the population, at least in countries that have kept records, the condition has recently reached unprecented rates among children and young adults.

A National Institutes of Health study published in 2009 showed that myopia prevalence in the United States increased by 66 percent between the early 1970’s and the early 2000’s. Dr. Susan Vitale and her colleagues at the National Eye Institute compared data from 1971 to 1972 to surveys from 1999 to 2004. The surveys used the same examination methods for both periods of time to determine myopia in participants whose ages ranged from 12 to 54.

The researchers found that 41 percent of the sample had myopia, as compared to 25 percent three decades earlier. While myopia of all levels registered an increase, the data showed that severe myopia was twice as prevalent among younger adults (ages 20 to 39) as among the elderly.

All races included in the study showed a higher prevalence, but increase rates were greater for black participants than for white participants. "Black participants surveyed in 1971 to 1972 may have had less access to educational opportunities than white participants and consequently experienced less exposure to near work (a risk factor for myopia)," the authors wrote. "As racial inequities in educational opportunities decreased, near-work exposure may have increased relatively more in black participants than in white participants."

The 2009 study is hardly the first to suggest that an increase in years of formal education and access to technology across society may account for higher myopia rates in recent years. Ophthalmologists and optometrists have cautioned that close-up activities like reading and using computers, tablets, and smartphones interfere with normal blinking and put a strain on the eyes. When abused, they can lead to double vision, myopia, and serious conditions such as retinal detachment and vision loss. The overuse of handheld electronics such as iPads and tablets by young children is especially worrisome, since their eyes are still developing and are more likely to be affected, according to researchers at the University of California, Berkeley.

Kathryn Rose, a researcher of visual disorders at the University of Sydney's college of health sciences, recently concluded  that spending too much time indoors also has a huge impact on eyesight deterioration. Rose said in a CNN interview that she was not sure how time spent using digital media relates to myopia progress, but that outdoor light has been shown to have a positive effect on vision. Studies from the U.S., Singapore, and China confirm a link between the time spent outdoors and the prevention of myopia, Rose said. However, both the level of light and the duration of exposure to outdoor light must reach a certain threshold to have a preventive effect, according to one of her studies. Spending at least 10 to 14 hours outside per week may prevent the early onset of myopia, she concluded.

The sudden surge in myopia cases in the past few decades, as documented by Vitale's 2009 study, prompted researchers and policymakers to look for answers to what may become a costly public health issue. If 25 percent of those aged 12 to 54 years in the U.S. had myopia, direct medical costs and associated productivity losses  would amount to  more than $2 billion per year; an increase in prevalence to 37 percent would increase the cost to more than $3 billion, according to the National Institutes of Health study.

The Japanese city of Kariya went as far as banning smartphone use for elementary and junior high school students after 9 p.m. starting last month, partly to reduce the strain on their eyes, according to The Japan Times.

In the U.S., eye doctors at the University of California, Berkeley, founded a specialized clinic to combat the rise in myopia among children. Dr. Maria Liu, head of the Myopia Control Clinic that opened last year, explained that prevention and treatment success depend on early detection. Nearsighted children under 10 could benefit the most from intervention. This age group is also the most susceptible to eye damage from prolonged use of visual media, according to the myopia specialist.

"The eyeballs are very adaptive while they are developing," Liu told me. "If we impose a lot of near work on the eyes as they are developing, the eyes will interpret nearsightedness as being the normal state."

Computers, tablets, and video games require specialized motor skills that young eyes have yet to develop. Mature, completely formed eyes have a better ability to cope with the visual stress from such devices.

"The earlier the onset of myopia, the later it tends to stabilize (once the growth process is complete), and the faster the progression," Liu said. Some children with myopia advance as fast as one or two diopters (the unit used to measure a lens’s optical power) per year, according to the specialist.

She explained the rise in myopia prevalence is likely caused by a shift in lifestyle from spending time outdoors to an indoor-oriented existence. Electronic devices play a major role in this shift, especially with young children being introduced to technology at an earlier stage in their life, and using handheld devices that require a smaller working distance than that for a physical book or television.

Although myopia rates are relatively low in agricultural regions and nations, the difference is most likely associated with academic work and near work demands, and has less to do with outdoor light intensity. "The higher the academic stress, the higher the prevalence and the earlier the onset of myopia," Liu said, noting there are differences even between school districts in the same city. If spending a certain amount of time outdoors had a significant effect on myopia, we should see prevalence rates vary geographically based on light intensity, she said.

Both genetic and environmental influences determine the early onset and the progression of myopia, but genetic studies have a hard time showing which inherited factors play a greater role: the parents' genes, their lifestyle, or both, according to Liu, who performs animal studies related to myopia.

When myopia debuts early, it has time to develop into something more severe, Liu explained. In pathological myopia, which is still relatively rare, the excessive elongation of the eyeball significantly increases the risk for retinal detachment, abnormal blood vessel growth, and other complications, which can lead to irreversible vision loss.

The Myopia Control Clinic specialists use corrective lenses (novel contact lenses) to slow down myopia in children. If applied early enough, corrective lenses have proven effective in treating the disorder. In cases with very high myopia progression, however, scleral reinforcement surgery is used to reduce or stop further damage caused by high myopia, which often can be degenerative.

Atropine is the only drug that so far has proven effective in slowing myopia progression. The drug is used as a second line of treatment after all optical treatments fail.

Although modern lifestyle makes it harder to fight the disorder, there is something parents can do to prevent its early onset. "Increasing outdoor activities is a very strong protective factor for myopia," Liu said. "Whether it is because hormonal levels are different outdoors, or because the light intensity is stronger, or because we do less close-up work, it has been shown consistently that outdoor activity is very protective and tends to slow the rate of progression."

Taking frequent 10-minute breaks from near-work and looking in the distance is also recommended, including for young adults who spend a lot of time working on computers or laptops and may suffer from accommodating spasms that cause blurry distance vision and dry eyes. The frequency of breaks depends on the working distance for each device. However, switching from reading a book to playing computer games is not a good break for the eyes, even though it may provide a break for the brain, Liu said.

Some specialists recommend limiting time in front of computers, TVs, and handheld devices to 1.5 hours a day, especially for young children.

"We don't have clear clinical evidence showing what is the cutoff for close-up activity that can help prevent myopia," Liu added. "I think it's more about taking frequent breaks."

Liquid crystal display monitors and protection glasses designed for monitors may minimize the strain visual media place on children's eyes. Parents are also advised to take children in for annual ophthalmological exams, and watch for any vision problems, especially in young children who might have a hard time communicating them.