Myopia is experiencing an epidemic rise across the world, most dramatically among younger people (college educated and high school graduates) in East and South Asia where the prevalence has reached almost 100 percent in some demographics.1-6
Myopia is now one of the leading causes of vision impairment and blindness in the world.7 The prevalence of myopia has increased steadily during the last half of the 20th century and into the 21st century in most parts of the world,1,8-10 and is estimated to affect 50 percent of the world’s population by 2050 (Figure 1).1,8-11
The increasing prevalence of myopia has emerged as a global health concern because of sight-threating pathologies like myopic macular degeneration, choroidal neovascularization, cataract, and glaucoma associated with high myopia.12Related: How to build a myopia control practice
Despite creating a major health burden, the exact mechanisms of myopic eye growth and its progression, particularly in the juvenile population, remain unknown.13
Hyperopic eyes of human infants and of infant monkeys made hyperopic with negative trial lenses experience coordinated growth, resulting in longer eyes and a refractive trend toward emmetropia (emmetropization).12,14 Juvenile myopia can be considered a failure of emmetropization or a possible reactivation of the emmetropization mechanisms in later childhood in response to chronic hyperopic defocus produced by habitual near viewing and accommodative lags.15
The second hypothesis could reflect eyes successfully adapting to the modern (near) environment. The high prevalence of myopia among populations that spend a lot of time doing near vision tasks (school children, high school and college students, and those in religious seminaries) further support the hypothesis that hyperopic defocus (central or peripheral) generated by accommodative lags during near work could stimulate eye growth (Figure 2).16-18Related: How to control myopia progression in your practice
Several important technological developments have occurred during the same general time period as the emergence of the myopia epidemic:
• The number of digital information sources (Internet host sites) climbed from about 100 in 1980 to 1 billion by 2012.19
• In the early 2000s, the number of worldwide smartphone users were reported to be 1.85 billion (190 million in U.S.) and are projected to rise to about 3 billion (272 million in U.S.) by 2020.20,21
• Total worldwide cellphone subscription rate has exceeded the 7.5 billion worldwide population, passing over 8 billion in 2018.22
• People are now engaged in viewing behaviors unavailable prior to the 21st century, such as entertainment videos, photos, Internet, social media, and work-related viewing on a display that may be only a few centimeters wide.23
The progressive improvement in spatial resolution of electronic displays from video home system (VHS) in the 1970s is astounding. This increased resolution has resulted in a corresponding reduction in display sizes, yielding high-quality handheld displays of only 14 x 7 cm that can be viewed at distances less than 25 cm without detection of individual pixels.23Related: How digital device usage is affecting youth
A 2017 report by the nonprofit Common Sense Media suggests that in the U.S., 98 percent of households with children under 8 years of age have a mobile device.24 Plus, 42 percent of children age 8 and younger and 66 percent of teens and tweens aged 8-18 years have their own mobile devices.25 The average usage time in this young and adolescent group is reported to exceed 4 hours and 6 hours per day, respectively.24,25
With advancement in technology over time, electronic display viewing is transitioning from traditional computers to handheld personal devices and thus, increased exposure time at short viewing distances.26
Could these changes be implicated in the worldwide myopia epidemic? Have we become victims of our own technological success?
Related: Know the legal aspects of myopia control
In a recent study, my colleagues and I examined the accommodative accuracy of emmetropic and myopic children as they viewed a range of targets displayed on electronic devices.
We used a sensitive autorefractometer (WAM-5550) to monitor refractive states of children (sampling frequency= 5Hz) as targets were moved from distance (4 m) to near (20 cm).
We found that, at near, small amounts of hyperopic defocus were present in all children. At viewing distances typically employed with handheld electronic devices (33-20 cm), emmetropic and myopic children experienced similar lags (mean 0.54 and 0.32 D, respectively) to those previously reported with printed materials.27,28
We found no evidence that electronic displays generated elevated accommodative lags and elevated magnitudes of hyperopic defocus. Therefore, if electronic displays are a causative factor in myopia development, it is likely due to increased duration of exposure to near targets, not the magnitude of the hyperopic defocus they produce.29
Moreover, the increased exposure to sunlight during time spent outdoors increases the release of retinal neurotransmitter dopamine which has been postulated as a preventive factor for myopia progression.30,34 With increased use of electronic devices, children may be less motivated to play or spend time outdoors and may prefer to remain indoors. 31-33
For example, estimates from 2012 indicate that in the U.S., juveniles spend 35 times more time on screens/electronic devices than in vigorous physical activity (7 hours 11 minutes per day on screens versus 12.6 minutes in physical activity).34,35Related: How to recognize and manage digital eye strain
Consistent with the “failure of homeostasis”15 (an emmetropic eye failing to remain so with time) or alternatively a reactivation of emmetropization mechanisms in response to hyperopic defocus, several strategies have been implemented worldwide in efforts to avoid myopia or to slow myopia progression by reducing chronic exposure to hyperopic defocus in juveniles.
Bifocal spectacles and progressive addition lenses (PALs) were the first line of treatment and reported to relieve optical blur as a result of prolonged accommodation.31
Another approach sought to remove hyperopic defocus from the peripheral retina by introducing myopic refractions in the peripheral cornea via orthokeratology or multifocal contact lenses designs.36
A pharmacological tactic with drugs inducing cycloplegic effects (atropine and pirenzepine) has also been used to slow myopia progression.37,38
Related: Treating and diagnosing myopia
Other methods to prevent children from using short viewing distances for prolonged duration include putting mechanical bars on school desks in China, software interventions in smartphones which flicker warnings if used too closely, and increasing outdoor play time.39-41
Earlier onset of myopia is associated with larger amounts of myopia later in life, increasing the loss of sight risks linked to high myopia.42,43 Similarly, having early emmetropia (absence of significant hyperopia-<+0.50 D) at school entry is reported to be a major risk factor for later myopia development.31
A study of school children in Taiwan reports that outdoor activity during school recess delayed the onset of myopia, supported by a 2017 meta-analysis.41,44 Increased time outdoors, however, failed to slow myopia progression in already myopic eyes.44
These reports converge to suggest that adopting preventive measures early in life is essential to delay the onset of myopia, which might then prevent higher amounts of myopia later in life.
Our study reveals that children using personal electronic devices will experience accommodative lags (hyperopic defocus)-but despite this, at this time no direct link has been established between the usage time for handheld electronic devices and myopia development. Further research is warranted to continue to explore the relationship of modern digital devices in myopia development-this is a question that needs an answer in the modern technological world we now live in.
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