Screentime and Near Work Differential Effects in Young People

In younger adults, however, the reason for changes in refractive error is unclear. Height growth is thought to have ceased by late adolescence and senescence cataracts are rare during young adulthood. Yet, the Raine Study in Western Australia reported that myopia continues to progress in one in three people during their 20s. Out of every seven people who were not myopic at age 20, one would develop myopia within the next decade of life.¹

YOUNG ADULTS AND THE ‘MILLENNIAL’ GENERATION

The current generation of young adults is part of the ‘Millennial’ generation and is a particularly interesting group to study. Millennials are the first generation to grow up with the internet; handheld mobile phones became ubiquitous in their teenage years; and smart phones became the dominant type of mobile phones early in their adult life.

Given that personal digital devices became common only in the past 10–20 years, the longterm effects of digital screens on the eyes and refraction are as yet unclear. But if we are to first notice it in someone, it would be a Millennial.

MYOPIA AND ENVIRONMENTAL RISK FACTORS

Findings on myopia associations with screen time or near work have been weak and inconsistent,² in contrast to less time spent outdoors, which has been proven by randomised controlled trials to be causally linked to myopia.

Limitations of most studies that have explored screen time or near work have included the inability to account for time spent outdoors and the separate evaluation of different types of screen time. Viewing distance and screen size vary widely between devices and thus are likely to have varying effects on myopigenesis. In the Raine Study, we investigated associations between three different types of screen time – television, computer, and mobile devices – and myopia, accounting for outdoor sun exposure.³

TELEVISION

Typically viewed at a distance of 1.5–4 m, television watching is not generally considered a near activity. Nonetheless, it is arguably the first common type of digital screen. Despite misconceptions that television is bad for the eyes, studies have consistently found no association between television watching and myopia.³ Furthermore, in developed countries, televisions became common in households in the 1970s – when the ‘Baby Boomer’ generation was in childhood – and we have yet to notice any ill-effects of television watching in this cohort.

COMPUTERS AND LAPTOPS

Desktop computers became common in schools in the late 1990s, with widespread use of household computers and the internet by the late 1990s to early 2000s. The increasing use of computers has led to concerns of digital eye strain, which has been hypothesised to be due to short-wavelength visible light, or blue light, emitted by the computer. However, there is no evidence that blue-blocking lenses are effective in relieving digital eye strain.⁴

Nonetheless, associations between increased computer time and myopia have been found, even after accounting for time outdoors.^3,5 In the Raine Study cohort, we found that those who reported having computer screen time of consistently more than eight hours per day between the age of 20 and 28 years had faster myopia progression and axial elongation by up to 139% compared to those who used the computer for less than six hours per day over the eight years.³

Importantly, this effect of computer screen time was not affected by the amount of ocular sun exposure, suggesting that increasing outdoor time is unlikely to offset the myopigenic effect of computer screen time.

MOBILE DEVICES

The screens on mobile devices are typically small – only about 7.5 cm wide for the larger smart phones – and correspondingly display smaller texts and are viewed at a shorter distance. Upon initial consideration, this should mean that mobile device screen time is more myopigenic than computer screens and traditional pen-and-paper near work. Yet in the Raine Study, we failed to find any associations between mobile device screen time and myopia progression between 20 and 28 years old.

This is quite counterintuitive. After all, a prolonged shorter viewing distance with near work has been linked to myopia progression in several studies.^6,7 However, these studies were based on traditional pen-and-paper near work.

PERIPHERAL DEFOCUS

The reason for these surprising findings may come down to peripheral defocus, which is an underlying mechanism for myopia development and progression. That is, during near work, even though the central image is focussed on the retina, peripheral rays entering the eye still form the image behind the retina (hyperopic peripheral defocus) due to the curvature of the globe, triggering the eye to elongate. This is the theory behind which many modern myopia control spectacles and contact lenses, including orthokeratology, were based. The proven effectiveness of such optical methods, such as Stellest (HALT – highly-aspheric lenslet target technology) by Essilor, is evidence that reducing peripheral hyperopic defocus during near work could be protective against myopia.

In traditional pen-and-paper near work, the paper or book is usually relatively bigger in size and placed on a flat table-top surface. The closer the working distance, the greater the hyperopic defocus. Mobile phones, on the other hand, are often handheld (Figure 1). Thus, despite the greater focussing demand of smart mobile devices, the small size of the devices means that objects behind the mobile phone are further away, leading to a relative myopic defocus. A study in Queensland⁸ confirmed this phenomenon when comparing peripheral defocus between pen-and-paper and smartphone use. A 2019 study in Singapore⁹ even found a mild protective effect of mobile phone use against myopia in adolescence.

Figure 1. Traditional pen-and-paper near work (left) tends to be done on a flat surface such as a table, is larger in size, and projects a larger degree of arc compared to using a mobile phone, which is often handheld (right). This may explain why closer working distance for traditional near work is linked to worse myopia outcomes, but not mobile phone screen time.

Computers have larger screens and, even if viewed at a further distance, span a larger angular size on the retina compared to mobile devices. In theory, this would lead to greater peripheral hyperopic defocus. While this effect has not been tested experimentally, it is a likely explanation for the myopigenic effect of long hours of computer use in the young adults of the Raine Study. The different screen sizes, viewing distance, and resultant retinal image sizes are shown in Table 1.

Table 1. Typical or average screen size, viewing distance, and resultant retinal image size of common digital screens.

INTERVENTION

In this day and age, it is difficult or even impossible to avoid computer use. Changing our habits to increase working distance and decrease time spent on digital devices may not be practical. Moreover, it is not uncommon for office workers to have a second monitor or for gamers to have a curved monitor, which increases relative peripheral hyperopic defocus. I, for example, have a computer-heavy occupation and will not be willing to trade the convenience of a second monitor for a lower risk of myopia progression.

Instead of limiting screen time in young adults, and even older children who may need a computer for schoolwork, we could implement other myopia control methods. In theory, orthokeratology and other optical interventions that leverage peripheral defocus, including highly aspheric peripheral rings, would be very effective in directly countering the peripheral hyperopic defocus induced by large screens (although these have yet to be empirically studied). For example, spectacle lenses that use highly aspheric lenslet technology have a centre spherical component of 9 mm in diameter surrounded by concentric rings of aspheric lenslets to reduce hyperopic defocus in the peripheral retina, while following its shape, regardless of the direction of gaze. At a vertex distance of 12 mm, the centre ring would only span ~40°, which is smaller than that spanned by desktop monitors, and therefore could counter the effects of peripheral focus induced by these large digital screens. Low-concentration atropine is also likely to be effective, albeit in a more indirect way by possibly exerting its effects via the choroid.¹⁰

MOVING FORWARD

At the time of writing there were several published statements providing variable guidance on myopia control including:

• IMI Clinical Management Guidelines paper published in 2019, with two updates in 2021 and 2023: iovs.arvojournals.org/article. aspx?doi=10.1167/iovs.18-25977
• WCO Resolution on The Standard of Care for Myopia Management (Optometry), 2021: worldcouncilofoptometry.info/resolution-thestandard- of-care-for-myopia-managementby- optometrists.
• New World Council of Paediatric Ophthalmology and Strabismus Myopia Consensus Statement, 2023: wspos.org/ swdcore/uploads/WSPOS-Myopia- Consensus-Statement-2023-1.pdf.
• Newer European Society of Ophthalmology in cooperation with International Myopia Institute ‘Myopia management algorithm’, Dec 2023: pubmed.ncbi.nlm.nih.gov/38087768.

Newer European Society of Ophthalmology in cooperation with International Myopia Institute ‘Myopia management algorithm’, Dec 2023: pubmed.ncbi.nlm.nih.gov/38087768. It is thus up to clinicians to personalise myopia control treatment for each patient. For example, it may not be prudent to recommend myopia control to all young people in their 20s as myopia progression will naturally stabilise for the majority. On the other hand, a 20-yearold with a computer-heavy profession and myopia progression of -0.50D in a year might benefit from treatment. Such interventions are especially important if myopia onsets during late adolescence or early adulthood. As we have previously described,¹¹ there was a case where low myopia (-0.50D) onset during a patient’s early 20s progressed to -11.00D in their 30s, leading to pathological myopia about a decade later. Such late onset of myopia may suggest that myopia progression has only just began.

Dr Samantha Lee completed her PhD in 2017 at the Queensland University of Technology. She is now a Senior Research Fellow at the Lions Eye Institute and the University of Western Australia. She has published over 50 peer-reviewed articles, with her current research focussing on the genetics and epidemiology of glaucoma and myopia.

References

1. Lee, S.S., Lingham, G., Sanfilippo, P.G., et al., Incidence and progression of myopia in early adulthood. JAMA Ophthalmol. 2022;140(2):162169. DOI: 10.1001/ jamaophthalmol.2021.5067.
2. Morgan, I.G., Wu, P.C., Ostrin, L.A., et al., IMI risk factors for myopia. Invest Ophthalmol Vis Sci. 2021;62(5):3. DOI: 10.1167/iovs.62.5.3.
3. Lee, S.S., Lingham, G., Wang, C.A., et al., Changes in refractive error during young adulthood: The effects of longitudinal screen time, ocular sun exposure, and genetic predisposition. Invest Ophthalmol Vis Sci. 2023;64(14):28. DOI: 10.1167/iovs.64.14.28.
4. Singh, S., Downie, L.E., Anderson, A.J., Do blueblocking lenses reduce eye strain from extended screen time? A double-masked randomized controlled trial. 2021;226:243251. DOI: 10.1016/j.ajo.2021.02.010.
5. Enthoven, C.A., Tideman, J.W.L., Klaver, C.C.W., et al., The impact of computer use on myopia development in childhood: The Generation R study. Prev Med. 2020;132:105988. DOI: 10.1016/j.ypmed.2020.105988.
6. Huang, P.C., Hsiao, Y.C., Tsai, C.Y., et al., Protective behaviours of near work and time outdoors in myopia prevalence and progression in myopic children: a 2-year prospective population study. 2020;104(7):956–961. DOI: 10.1136/bjophthalmol-2019-314101.
7. Wen, L., Cao, Y., Cheng, Q., et al., Objectively measured near work, outdoor exposure and myopia in children. 2020;104(11):1542–1547. DOI: 10.1136/ bjophthalmol-2019-315258.
8. Read, S.A., Alonso-Caneiro, D., Hoseini-Yazdi, H., et al., Objective measures of gaze behaviors and the visual environment during near-work tasks in young adult myopes and emmetropes. Transl Vis Sci Technol. 2023;12(11):18. DOI: 10.1167/tvst.12.11.18.
9. Toh, S.H., Coenen, P., Straker, L.M., et al., Mobile touch screen device use and associations with musculoskeletal symptoms and visual health in a nationally representative sample of Singaporean adolescents. Ergonomics. 2019;62(6):778793. DOI: 10.1080/00140139.2018.1562107.
10. Sander, B.P., Collins, M.J., Read, S.A., Short-term effect of low-dose atropine and hyperopic defocus on choroidal thickness and axial length in young myopic adults. J Ophthalmol. 2019;2019:4782536. DOI: 10.1155/2019/4782536.
11. Lee, S.S.Y., Myopia in young adults: Is onset and progression important? mivision, 2023 Jun (190);76.