Analysis: the main challenges to children's visual systems are how close children hold screens and how long they use screens

In recent years, there has been an alarming increase in people with myopia (shortsightedness). Over two generations, myopia rates increased fourfold in Asia and doubled in the UK, with children becoming myopic at younger ages. By 2030, 2.5 billion people may be affected, so finding ways to stop this growing issue is crucial.

Myopia, caused by the eye growing too long, results in light entering the eye, focusing in front of instead of on the retina (the eye's light-sensitive layer) and resulting in blurred distant vision. As the eyeball elongates, the retina stretches and thins and is prone to tearing, resulting in visual impairment in mid to later life. Myopia is progressive; the earlier a child develops myopia, the more likely they will have severe myopia in adulthood.

Parental history raises a child's risk of developing myopia. However, rising myopia rates are happening too fast to be solely genetic and are mirroring lifestyle shifts, including congested living conditions, reduced outdoor time and daylight exposure, and more screen time.

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From RTÉ Radio 1's News At One, Dr Síofra Harrington on why children are more likely to be shortsighted if they are heavy screen users

Our research at TU Dublin focused on children's vision and engagement in near activities (screens and reading) and daylight exposure. The Ireland Eye study sampled 1,626 schoolchildren from 37 urban/rural randomly selected schools in Ireland. One in three participants, and well over half of the children with myopia, exceeded the WHO maximum two hours a day screentime recommendations. Increased screentime was associated with longer eyes, higher myopia, and higher BMI. Children outdoors for two or more hours a day had better vision, were less likely to need glasses, and had a healthy BMI. Children outdoors less than one hour a day were five times more likely to be myopic than children that who were outdoors over two hours a day. Our research found screentime has eclipsed reading in 'digitods' (those born after the launch of smartphones in 2008).

Near-work and increased education levels are long associated with myopia. For example, Singapore introduced significant educational reforms in 1978, which resulted in intensive schooling and academic pressure; myopia rates increased dramatically from 40% to over 90% by 2000. However, pandemic control measures demonstrated school is not the problem; school-lockdowns led to rapidly increased and accelerated myopia levels, particularly amongst six to seven-year-olds. During lockdown, children stayed indoors on screens when school and other activities disappeared, resulting in 'Quarantine myopia'.

The main challenges to children's visual systems are how close children hold screens and how long they use screens. Children hold screens close to their faces, increasing demand on the eye's focusing system. Our central vision is clear when we focus on a nearby object, like a smartphone. Yet, things further away in our peripheral vision remain blurred as light rays entering the eye fall behind instead of on the retina in the periphery area (peripheral defocus).

Figure showing the difference between a normal eye and a myopic eye Photo: Síofra Harrington

Peripheral defocus leads to biochemical signals telling our eye to correct the issue by elongating so light rays fall on the retina. The more the eye tries to fix the peripheral defocus by growing longer, the worse myopia becomes. Extended periods on screens compound exposure to this defocus. Eventually, the back of the eye can become prolate-shaped (egg-shaped), with the posterior pole protruding (figure above).

With 87% of three to four-year-olds online, one in five three-year-olds, and almost 90% of 11-year-olds owning a phone, the potential acceleration of myopia progression in young children is concerning.

What are the benefits of sunshine?

Light is necessary for vision and daylight is a natural source. Typical indoor light-levels, even in rooms with windows (100-150 units of illuminance (lux)), are lower than outdoors, ranging from 11,000 to 18,000 lux. Even in the shade wearing sunglasses, outdoor light levels are 11 to 43 times higher than indoors. Bright light stimulates the retinal neurotransmitter dopamine release, stabilising eye-growth and inhibiting myopia. Interestingly, as daylight hours lengthen, eye elongation and myopia progression decrease.

Reduced time indoors and on screens may be as crucial as being outdoors. Spending time outdoors encourages children to focus on distant objects like trees, birds flying, and teammates playing games — anything more than arm's length away reduces focusing demand. Also, daylight/bright sunlight constricts the eye's pupil decreasing peripheral defocus. Daylight is a natural 'zeitgeber' or time-cue for synchronising our internal circadian rhythm due to fluctuations in daylight intensity and spectral distribution throughout the day. Artificial lighting disrupts circadian rhythms, destabilising eye-growth— notably, children with high myopia report later bedtimes and poorer sleep quality.

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From Vox, why so many people need glasses now

With increased numbers of children living in overcrowded settings, the relationship between myopia and built environment (building density, living space, and green environment), are critical concerns. There is a minimum level of illumination appropriate for classrooms -- above 300 lux on desks and above 500 lux on school white/blackboards to slow eye growth.

The 30/30 rule

Children's visual environment influences their vision, eye health and general health – positively and negatively -- depending on how much time they spend outdoors and what activities they undertake indoors.

Children holding screens close to their faces for extended periods indoors and getting less daylight exposure are at increased risk of myopia and faster-progressing myopia. Screentime has replaced reading, TV and outdoor time. Children should spend breaks outdoors during preschool and primary school, as their visual system is particularly vulnerable to indoor visual environments. The recommended daily outdoor time is two hours, which could be 15 minutes walk to school, 30 minutes outside at lunch break and 15 minutes walking home with an hour outdoors before homework. When children want screentime, remember the 30 – 30 rule; hold screens no closer than 30cm for 30 minutes, then take a break, preferably outside.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ