There is no denying that there has been a significant onslaught in the use of technology by our children and teenagers, as the world around us becomes more reliant on screens, all of the time. Children are accessing screens at school, around the home and for personal entertainment at younger and younger ages. At the same time, there has been an unprecedented increase in myopia in children, with higher numbers and earlier age of onset. So is this correlation or causation? It’s a tidy idea to blame the screens, but nothing is ever that simple. Increased screen time can be associated with more near work, more indoor time and less outdoor exposure. So how much are the screens themselves to blame for the myopia epidemic?
Screen time and myopia - causation or correlation?
Is myopia caused by screen time, or are they co-existing features of the modern visual environment? The increase in myopia rates occurred before the saturation of screens in society, with rates of short sightedness in East Asia increasing before the technology took hold.1 A 2020 meta analysis by Lanca et al. showed no significant association between screen time and myopia, but they do admit that even when no statistical association was found, children who were myopic spent more time using screens. A literature review by Recko et al. also suggested a weak correlation between electronic devices and myopia rates - they instead focused on parental myopia.2
We do know there is an association that children whom spend limited time outdoors, and more time at near have increased rates of myopia, and it may simply be that the screens have replaced other near work modes.1 This could be supported by the fact that whilst screen time has dramatically escalated in children, the myopia rates, whilst increasing, have not exponentially exploded.
How do we find a link between screen time and myopia?
Part of the challenge is that in order to ascertain device usage, most studies use surveys and questionnaires immediately compromising the data, which are likely not as reliable as objective measures. I know I would certainly play down the amount of time I spend on social media! A novel survey by McCrann et al used data usage as an objective measure of time spent on the device, and correlated that to frequency of myopia.3 They found a significant relationship between increased data usage and myopia - the myopes used almost twice as much data per day as non-myopes. As a cross-sectional study, the authors were unable to measure the impact of screen time on myopia progression, but they did find that more data usage co-existed with higher myopic refractive error.
How much are children actually looking at screens?
A study conducted in Philadelphia suggested that at age four, half of children had their own television and three-quarters had their own mobile devices.4 The McCrann et al data usage study suggested that teenagers dedicate double the time to smartphone use than they do to all other near work, and each younger age group spends more time in bed on the devices than the one before them.3 A 2011 study published in the Journal of Paediatrics suggested 47% of children were spending more than two hours a day on screen time for entertainment,5 and by 2019 that number had skyrocketed to 98% in the US.6
What else could it be?
Tang et al released a 2020 population based, cross-sectional surgery looking at the risk factors behind myopia development. They used the Hong Kong Children Eye Study, and found that after statistical adjustment, the strongest relationship is to parental myopia, and the higher the myopia the clearer the association. Parental myopia won out against device time and any other factors.7
How else can screen time affect eye health?
Here's two things found in the scientific literature on how smartphones can influence visual function and eye health in children.
Smartphone use can cause acquired esotropia in adolescents. A retrospective case series of 12 children aged 7-16 years with acute acquired comitant esotropia (AACE) and no other mechanical or neurological cause found their average duration of smartphone usage was 6 hours a day, for a mean 10 months prior to the eye examination. Onset of the esotropia was almost 6 months prior to clinical presentation (evidenced in prior photos) and all used their smartphones at <30cm viewing distance. Eight were myopes (average -3.8D) and four were mild hyperopes (average +0.8D) and all had unsuppressed esotropia with similar distance and near deviations in the range of 15 to 45 prism dioptres (PD). All were firstly asked to refrain from smartphone use for a month - the mean esodeviation reduced from 28 to 18 PD. Three with esodeviations greater than 30 PD proceeded to surgery, with ortho results. The other nine showed no change from their post-1 month smartphone break appointment to final follow up, 3-11 months later.
Smartphone use is a risk factor for paediatric dry eye disease (DED). In a study of 630 children in South Korea aged 6-13 years, 9% of older children (Grades 4 to 6) and 4% of younger children (Grades 1 to 3) had DED, and spent an average of 3.2 hours a day on smartphones compared to 0.6 hours / day in normals. Normals spent 2.3 hours a day while children with DED spent 1.5 hours a day outdoors. After a month of smartphone cessation, all children with DED showed improvment in their subjective and objective signs.
What advice should we be giving our patients and their parents?
When families pay attention to their media consumption and parents monitor their children’s digital access, the amount of screen time reduces along with positive improvements in sleep and school performance.8 We know there is a protective effect of outdoor time on the onset of myopia, so it is sensible to recommend outdoor time away from any near activities. The World Health Organization recommends at least 60 minutes of moderate to vigorous physical activity for school aged children per day, yet a UK survey found that three-quarters of UK children aged 5-12 years spend less time than this outside - which is less time spent outside than prison inmates! Shockingly, 20% of the children surveyed never play outside regularly. When it comes to myopia prevention, though, it’s not the physical activity that is the crucial element, it is likely the light exposure9 - so to combine both benefits, this physical activity time can be undertaken outdoors.
Advise your patients and their parents to:
- Reduce screen time: the Australian Department of Health and the American Academy of Paediatrics recommend less than two hours per day of leisure screen time for school-aged children
- Get at least 60 minutes of moderate to vigorous intensity physical activity: recommended by the World Health Organization for children aged 5-17 years
- Be sun safe and protect from UV when outdoors: especially for those of us in Australia!
These measures are beneficial for a child’s physical and social development, and their myopia risk too. Resources to help parents learn about screen time can be found at My Kids Vision:
- Close Work and Screen Time in Kids
- How Much Time Should My Child Spend Outdoors
- How-To Video Guides - these are freely able to be shared on your practice websites, via email and on social media. Two videos cover close work and outdoor time habits for children; and maintaining a healthy visual environment for children during pandemic restrictions and schooling from home.
- Lanca, C. & Saw, S. M. The association between digital screen time and myopia: A systematic review. Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians 40, 216-229, doi:10.1111/opo.12657 (2020). https://onlinelibrary.wiley.com/doi/full/10.1111/opo.12657
- Recko, M. & Stahl, E. D. Childhood myopia: epidemiology, risk factors, and prevention. Mo Med 112, 116-121 (2015). https://pubmed.ncbi.nlm.nih.gov/25958656/
- McCrann, S., Loughman, J., Butler, J. S., Paudel, N. & Flitcroft, D. I. Smartphone use as a possible risk factor for myopia. Clinical and Experimental Optometry n/a, doi:10.1111/cxo.13092. https://onlinelibrary.wiley.com/doi/10.1111/cxo.13092
- Kabali, H. K. et al. Exposure and Use of Mobile Media Devices by Young Children. Pediatrics 136, 1044-1050, doi:10.1542/peds.2015-2151 (2015). https://pediatrics.aappublications.org/content/136/6/1044
- Maniccia, D. M., Davison, K. K., Marshall, S. J., Manganello, J. A. & Dennison, B. A. A Meta-analysis of Interventions That Target Children's Screen Time for Reduction. Pediatrics 128, e193-e210, doi:10.1542/peds.2010-2353 (2011). https://pediatrics.aappublications.org/content/128/1/e193
- Madigan, S., Browne, D., Racine, N., Mori, C. & Tough, S. Association Between Screen Time and Children’s Performance on a Developmental Screening Test. JAMA Pediatrics 173, 244-250, doi:10.1001/jamapediatrics.2018.5056 (2019). https://jamanetwork.com/journals/jamapediatrics/fullarticle/2722666
- Tang, S. M. et al. Independent Influence of Parental Myopia on Childhood Myopia in a Dose-related Manner in 2055 Trios: The Hong Kong Children Eye Study. American journal of ophthalmology, doi:10.1016/j.ajo.2020.05.026. https://www.ajo.com/article/S0002-9394(20)30265-8/abstract
- Gentile, D. A., Reimer, R. A., Nathanson, A. I., Walsh, D. A. & Eisenmann, J. C. Protective effects of parental monitoring of children's media use: a prospective study. JAMA Pediatr 168, 479-484, doi:10.1001/jamapediatrics.2014.146 (2014). https://www.academia.edu/13206526/Protective_Effects_of_Parental_Monitoring_of_Children_s_Media_Use
- Read, S. A., Collins, M. J. & Vincent, S. J. Light Exposure and Eye Growth in Childhood. Investigative ophthalmology & visual science 56, 6779-6787, doi:10.1167/iovs.14-15978 (2015). https://iovs.arvojournals.org/article.aspx?articleid=2466239