The visual environment in myopia

Understanding the risk factors in the development and progression of myopia has become more and more important in the wake of the rapid rise in myopia prevalence worldwide in recent decades. Genetic and personal risk factors for myopia include parental history of myopia, refractive error, age, and binocular vision status.¹ Many of these are not modifiable. Identifying these factors in your patients can provide an indication of their risk profile for myopia development. 

Being able to implement proactive measures to reduce the risk of myopia onset on the other hand, requires the presence of modifiable risk factors. The impact of the visual environment upon eye growth suggests the involvement of a number of different environmental factors, particularly for school-aged myopia. Because myopia tends to onset and progress during the schooling years, a lifestyle skewed towards intensive near work and less outdoor time has been thought to lead to myopia. Since these factors are modifiable, identifying opportunities to optimise the childhood visual environment should form part of a comprehensive myopia management plan.

Spending more time outside is the simplest lifestyle intervention we can advise for both at-risk pre-myopes and progressing myopes. It is well established now that increasing a child’s time outdoors helps to prevent or delay the onset of myopia.^2-4

Many cross-sectional studies on children from a range of countries have reported a significant association between greater outdoor activity and a lower prevalence of myopia. This rose to early prominence in the Sydney Myopia Study, some 15 years ago.⁵ Rose et al. found that 12-year-old students who combined low levels of near work with high levels of outdoor activity had the most hyperopic refractions. The students who combined high levels of near work with low levels of outdoor activity had the least hyperopic refractions.

Several longitudinal studies indicate a lower incidence of myopia in children who spend more time outdoors.^6-8

• Jones et al. found that children with incident myopia spent on average, 3-4 hours less per week on sports and outdoor activities compared to children who remained non-myopes.⁶ 
• To define the beneficial effect of outdoor time, Guggenheim et al. investigated the association of myopia with time outdoors and physical activity separately, and found a greater association for time outdoors than physical activity for incident myopia.⁸ Children aged 8-9 years who spent a “low” amount of time outdoors were about 40% more likely to have myopia by age 11-15, compared to those spending a “high” amount of time outdoors. Time engaged in physical activity was also associated with incident myopia but to a lesser extent, with about 10% more risk for children who were more sedentary.

We know that spending time outdoors is more important than engaging in any specific activity while outdoors. The mechanism is not fully understood, but there are several plausible theories. Increased light exposure while outdoors leads to pupil constriction (and an increase in depth of field), a decrease in blur, or increase in retinal dopamine which may inhibit axial elongation.⁹ Another viewpoint aligns with the peripheral retinal defocus theory of myopia that we see implemented in myopia control spectacle and contact lens designs today. Flitcroft et al. suggested that the dioptric environment outdoors contains a small amount of uniformly distributed myopic defocus, while the indoor dioptric environment contains a great deal of hyperopic defocus. Given the strong understanding of how the peripheral retina drives eye growth in both animal and human models, the benefit of outdoor time is likely to be a combination of the dioptric environment as well as light exposure.

The brightness of outdoor light may also be a factor, given the link between illumination and retinal dopamine activity.¹⁰ Research has shown that the brightness of outdoor light is much higher (11,080-18,176 lux) than indoors (112-156 lux), and even with sun protection including wearing a hat, sunglasses and seeking the shade, outdoor light is 11-43 times higher than indoors.¹⁰

Increasing outdoor time also appears to have a modest benefit in slowing down myopia progression.³ 

Furthermore, spending time outdoors benefits patients in non-ocular ways. Increased outdoor time in combination with physical activity will promote a healthier lifestyle in young patients, improving fitness and social and emotional wellbeing.^11,12 For delaying myopia onset, engaging in outdoor activities could replace sedentary (sitting) time and periods of inactivity.

There are three simple rules to prescribe for the outdoor visual environment – helpful for both reducing the risk of a child developing myopia as well as reducing the risk of fast progression.

1. Children and adolescents should aim to spend two hours per day outdoors. While this can seem hard to achieve in our busy lives, it may be mostly achieved at school for primary-school aged children, when this intervention is most crucial to prevent or delay myopia. On the weekend, a family outing – even a walk to the local park and a short play will help the minutes tick away.
2. Kids should be physically active for least 60 minutes a day. This should be moderate-to-vigorous level activity. If this is spent outdoors, all the better for their visual development. Again, for primary school aged children, this may be mostly achieved in break times.
3. Don’t forget sun protection – hats, sunglasses and shade. Children and adolescents will still get the vision, eye health and physical health benefits of time outdoors without excessive risk of sun exposure.

Children are heavily exposed to near work during the schooling years, as reading, writing, and screen-based work are integral parts of education. Due to the high visual demands of near work, and the tendency for myopia to develop during school years, excessive near work has long been implicated in myopia development. It has been proposed that accommodative lag during near work induces hyperopic defocus – a powerful stimulus for eye growth. The evidence to support an accommodative mechanism for myopia development remains controversial.¹³

Among young adults aged 18-25 years, myopia onset and progression are also fairly common. Certain population demographics require greater exposure to near work, such as university students in intensive study programs such as medicine and law, and occupations such as clinical microscopy.^14-17 Considering the duration of near work and the accommodative demands that may be involved, these could also be considered myopigenic in nature. One meta-analysis identified that the odds of myopia increased by 2% or every one diopter-hour more of near work per week.¹⁸ Nonetheless, understanding your patient’s near work behaviours should be of interest to eye care practitioners as a potential modifiable risk factor.

Screen-based devices

In more developed societies, the ubiquitous adoption of digital smart devices constitutes just as much near work as reading and writing. Handheld smartphones, for example, are used for longer durations and at closer distances than other forms of near work such as conventional books or computer screens.¹⁹ Approximately 68% of children before age 3 use screen-based devices on a daily basis, and those children who do are more likely to have developed myopia by pre-school age.²⁰ An increasing volume of research has linked screen time and myopia prevalence,²¹ myopic refraction,²² and longer axial length,²³ with the evidence most abundant for children under 16 within this crucial stage of visual development. At this stage, the literature suggests smart devices could be exacerbating the myopia epidemic, although there is limited data given their relatively recent introduction to the world.²⁴

Education

Level of education may act as a surrogate for increased involvement in near work. There is consistent epidemiological evidence suggesting that education has a causal role in relation to myopia, through various measures such as duration of education, educational achievement, and educational pressure. For example, the prevalence of myopia in Europe is higher in individuals who have completed higher education (37%) compared to primary (25%) or secondary education (29%).²⁵ The recent Global Myopia Prevalence and International Levels of Education study observed a significant positive association between national educational performance and myopia prevalence.²⁶ Some countries within the study exhibited a combination of high educational outcomes with low myopia prevalence. Such countries may serve as good models of educational policies to combat the growing myopia issue. 

There are three simple rules to prescribe for the indoor visual environment – helpful for both reducing the risk of a child developing myopia as well as reducing the risk of fast progression.

1. The elbow rule: keep an elbow-to-hand distance away from books and screens to avoid them being too close to the eyes.

2. The two-hour rule: try to limit leisure screen time (outside of schoolwork) to two hours per day in school-aged children, as per World Health Organization guidelines.²⁶

3. The 20/20 rule: take regular breaks from near work to reduce visual fatigue, eyestrain, and dry eye symptoms. As an easy guideline, suggest every 20 minutes, take a break for 20 seconds and look across the room. 

These rules are designed to protect against very close viewing distances and long durations of reading or screen time which are linked to myopia in children and teens.²⁷ Longer, sustained breaks of 5 minutes or more every hour may be even more effective to negate myopigenic effects.²⁸

The Myopia Profile Managing Myopia Guidelines Infographic is designed to support your clinical communication and decision making in myopia management. These engaging infographics summarize the evidence base for each step of the myopia management journey, and aids the decision-making process when making personalized recommendations for your young patients with myopia. It is comprised of two four-panel components or sides: one being the practitioner chairside reference, and the other being the patient-facing infographic to guide you through the clinical communication process. 

We developed the Infographics because using visual aids in health communications has been shown to improve learning and application of advice between health professionals, patients and their parents or carers. They are available to download and print in several formats and numerous language translations. Learn about Using the Managing Myopia Guidelines Infographics.

The very first panel of the patient-facing (multi-coloured) side explores recommendations for the childhood visual environment to support optimal childhood visual development and eye health, as a summary of the factors described in detail above. This theme is matched with an article on MyKidsVision.org, to which you can direct parents for further learning, entitled The childhood visual environment. 

The panel below is part of a set of four infographic panels to support clinical communication which describe visual environment advice, treatment options, contact lens wear in kids, and why myopia management is essential.

• Time spent outdoors is beneficial for physical and mental health in children and teenagers and has also been shown to reduce the risk of myopia. It may also play a small role in slowing myopia progression.
• Excessive, continuous near work and close working distances are linked to myopia development and progression in children and teenagers. Prolonged digital screen use is also associated with dry eye syndrome, digital eyestrain, and poor posture.
• Four simple recommendations are provided in the Myopia Profile Managing Myopia Guidelines Infographic, to promote a healthy childhood visual environment.