Myopia: Screens, Sunlight and the Rise of Nearsightedness

Image by ACSH using AI

What is Myopia 

Myopia, or nearsightedness, is a mismatch in which light rays focus in front of, rather than on, our retina. As a result, while close-up objects remain clear, distant objects appear blurry. August has been declared Myopia Month not to celebrate it, but to highlight the rising rates of myopia among the young. In a more agrarian time, 150 years ago, the incidence of myopia was roughly 20%; today in parts of the world the incidence is upwards of 90%. If we want to understand how humans have changed their environment and been changed in response, no case is better than myopia. 

Near Work: How the Eye Adapts

The eye compensates primarily by changing the shape of our lens, a process called accommodation. Through the parasympathetic fibers of our autonomic, unconscious nervous system, the muscles controlling the lens, the ciliary ring, cause the lens to steepen in curvature. This conformational change increases the eye’s refractive power to compensate for divergent wavefronts. To prevent double vision, the eyes turn inward slightly to maintain both eye visual axes on target, and the pupils constrict, increasing the eye’s depth of focus so small variations in accommodation do not create noticeable blur. As we age, we lose the lens's resilience, so we often need correction, most often through over-the-counter reading glasses. 

With near work, despite the in-the-moment accommodation, some light rays fall behind the peripheral retina – we focus primarily using the center of the retina or fovea. Those errant rays hitting the periphery set off a cascade of events that enlarges the distance between the retina and lens; our eye grows longer from front to back. 

Sunlight, Dopamine and the Developing Eye

While genetics influence our susceptibility to myopia, the “myopic boom” is predominantly an environmental response. In addition to near work, like reading and screen time, the developing eye, which we experience from age 5 to 15, has a critical deficit in natural daylight as we spend less and less time outdoors. Dopamine, released in the retina, is the biochemical messenger telling the eye to stop elongating. Near work depresses dopamine levels; daylight increases them. Without outdoor time, the dopamine brake on elongation turns off, and the eye continues to lengthen unchecked. 

High-intensity, full-spectrum daylight stimulates retinal photoreceptors, ultimately increasing dopamine levels, which, in turn, preserves the structural stiffness of the outer eye wall and slows elongation. Additionally, dopamine helps synchronize the eye’s circadian rhythm. Yes, as with all organs, the eyes change from day to night, enhancing high-acuity vision during the day and low-level vision at night through their differing effects on retinal cones and rods. 

Typically, the sun delivers 10,000 to 100,000 lux, a measure of visual light intensity; indoor lighting delivers far less, 300 to 500 lux. Chronic indoor light blunts the daytime dopamine peak, disrupting the eye’s circadian rhythm and permitting unchecked elongation.

The Global Myopia Epidemic

In 2000, roughly a quarter of the world population had some degree of myopia. That same meta-analysis predicted the percentage to rise to 50% by 2050. Two related factors appear to be causal: the time spent outdoors and that spent indoors doing near work

A meta-analysis found “Increased time outdoors is effective in preventing the onset of myopia as well as in slowing the myopic shift in refractive error. But paradoxically, outdoor time was not effective in slowing progression in eyes that were already myopic.”

A study from our old friend the UK Biobank noted: “strong evidence that more time spent in education is a causal risk factor for myopia.”

China’s Natural Experiment with Modern Childhood

In China, the poster-boy for the “myopia epidemic,” several factors highlight the risks of our modern-day environment.

• While Western urbanization occurred over periods of 100 or more years, China compressed that transition into roughly 40 years, moving hundreds of millions of families from open-sky agricultural landscapes directly into high-density, vertical concrete megacities. Children were moved to an environment without natural outdoor play, with effects on the eye’s circadian rhythms.
• China’s intellectual growth was powered by an educational meritocracy centered on competitive exams, which were the primary driver of socioeconomic mobility. During the years of critical ocular growth (ages 5-15), Chinese students typically have 8- to 10-hour school days, plus weekend academic supplements and tutoring. Their typical homework load is double the average for a country like the US.
• Downstream effects of maximizing instructional time include reduced outdoor recess and sports activities. While in 1960 a child might experience 3 or more hours of 50,000 lux daylight, urban Chinese students now typically experience roughly 30 minutes. 

China’s epidemiological data agree with these sociological transformations, and a meta-analysis predicts the incidence will double by 2050. An increase from the current incidence of 33% to 60% or more. 

What About Screens?

Print reading is not entirely benign, and low-light reading has driven myopia in the past. However, digital screens worsen the pathogenic variables by pulling the reading plane closer to the face, eliminating natural visual pauses, and displacing time spent outdoors in the sun.

A study in The Lancet found an increased risk of myopia with overall screen time, including phones and tablets, though it phrased the finding as “might.” As reported in JAMA Ophthalmology, using a rough measure of myopia designed for population health rather than definitive clinical diagnosis, there was a “substantial shift” toward greater myopia in school-aged children 6 to 8 years of age during the COVID lockdowns. It was not seen in older cohorts and suggested that early primary school was a pivotal developmental window. It was not seen as primarily an issue of near work, but rather a combination of near work and loss of outdoor time.

Can More Time Outdoors Protect Children’s Eyes?

Myopia is a striking example of how the modern environment reshapes our bodies. Genetics may determine susceptibility, but the rapid rise in nearsightedness points toward changes in childhood itself: more education and sustained near work, more time with screens, and far less time outdoors in bright natural light. The myopia epidemic is not a story about defective eyes but about normal eyes adapting to an environment very different from the one in which they evolved. While myopia was formerly simply a problem for high-income countries, the rest of the globe is catching up as they urbanize, increase educational opportunities, and stare into a variety of screens. 

August is Myopia Awareness Month, an apt time to recognize the rise in nearsightedness. It reminds us that protecting our children's sight may begin with something as remarkably simple as putting down the screen and going outside.