How much difference can sleep make to myopia risk?

Paper title: Sleeping late is a risk factor for myopia development amongst school-aged children in China.

Authors: Xiao Nicole Liu (1)(2), Thomas John Naduvilath (1)(2), Jingjing Wang (3), Shuyu Xiong (4), Xiangui He (3)(4), Xun Xu (3)(4), Padmaja R. Sankaridurg (1)(2)

1. Brien Holden Vision Institute Limited, Sydney, Australia.
2. School of Optometry and Vision Science, University of New South Wales, Sydney, Australia.
3. Department of Preventative Ophthalmology, Shanghai Eye Disease Prevention and Treatment Centre, Shanghai Eye Hospital, Shanghai, China.
4. Department of Ophthalmology, Shanghai General Hospital, Shanghai Jiao Tong University, Shanghai Key Laboratory of Ocular Fundus Diseases, National Clinical Research Centre for Eye Diseases, Shanghai, China

Date: Oct 2020

Reference:  Liu XN, Naduvilath TJ, Wang J, Xiong S, He X, Xu X, Sankaridurg PR. Sleeping late is a risk factor for myopia development amongst school-aged children in China. Sci Rep. 2020 Oct 14;10(1):17194.

[Link to open access paper]

Sleep quality and shorter sleep duration have been identified as risk factors for increased myopic refractive error in children^1,2 and altered light/dark conditions and wake/sleep cycles have been found to influence eye growth patterns in animal studies.^3,4

This 2-year long prospective school-based trial investigated the relationship between environmental and behavioural factors and myopia, particularly relating to sleeping patterns, for schoolchildren in Shanghai, China.

The ‘Shanghai Time Outside to Reduce Myopia trial’ gathered data on typical bedtimes and waking times from 6,295 children aged between 6-9yrs old from 24 Shanghai primary schools.

The schools were randomly assigned at baseline to either the control group or one of two test groups that spent either 40min or 80mins outdoors daily.⁵

Refractive error was confirmed by cycloplegic refraction at baseline and repeated annually. Parents provided information via a questionnaire on family history of myopia, the type of area they lived in (urban/suburban), their children’s specific bedtimes and waking times and the time they spent on various activities such as reading or being outdoors on a normal school day and on specific bedtimes and waking times.

The mean age of 6042 children at baseline was 7yrs, with 6.77% myopic. After 24mths, 27.64% of 5355 children were myopic. There were 4982 children not myopic at baseline but 1094 of these had become myopic by the 24mth visit, giving a 2-yr myopic incidence of 21.92%.

Baseline myopia and myopia incidence

Along with other known myopia risk factors such as age, living in an urban area, family of history and spending less time outdoors, late bedtimes and late waking were found to be associated with baseline myopia and myopia onset within the 2yr study period. Children who had a bedtime later than 9.30pm had 1.55-fold higher odds of being myopic at baseline, compared those whose bedtime was before 9pm.

Myopia progression

The mean average myopic progression for 5,305 children over the 2-year period was -0.92D +/- 0.77D. Over the 2yrs, 4% progressed by 1D, 2.61% progressed by 1.5D and 1.50% progressed by 2D. Progression was associated with late bedtime where children who had bedtimes later than 9.30pm had an average progression of 0.16D, increasing with later bedtime.

Sleep variables

Over 2yrs, bedtimes got later (average of 21:04 to 21:17) and waking times got earlier (6:34 to 6:27). Twice as many children went to bed at 10pm or later at the 2yr visit than at the start of the study. Overall, the children lost approx. half hour sleep per night by sleeping later and waking earlier. However, sleep duration was not found to be significant for myopia onset.

Children with later bedtimes were more likely to live urban areas, were older, had myopic parents, woke up later and spent more time reading or on screens than they did outside in a week.

Many parents will already be aware of the importance of sleep for their child’s overall health, well-being, and school performance. Children between the ages of 6-12yrs old are advised to consistently get 9-12hrs sleep every night.⁶

• The children in this study were between 6 and 9yrs old and at a development stage which is deemed prone to the onset of myopia or progression of existing myopia.
• Although parental myopia plays a genetic part which we can’t control, sleeping patterns are a behavioural risk factor which we can control and advise on.

This study found that the children who were more likely to have later bedtimes were also more likely to wake up later, spend more time reading or using screens and spend less time outside.

• When we discuss a child’s vision with them and their parents, we can ask questions on their typical sleep/wake patterns and advise on the importance of sleep and that the use of mobile phones/tablets in bed under artificial lighting could be delaying or disrupting sleep.

This study suggests that children who have later bedtimes may be more susceptible to myopia and experience more progression of myopia than those who have an earlier bedtime.

They may also be participating in myopigenic activities before bedtime such as close work or using digital screens in artificial light during the evening.

• The extra ‘dioptre-hours’ of close concentration may be the push factor rather than the late bedtime and that could be compounded by less outdoor time on the typical school days they monitored
• Animal studies have found lighting conditions can impact normal ocular growth and the emmetropisation process.^3,4,7 Other studies have found that compared to non-myopes, myopes may have higher serum of melatonin in the morning, sleep less and have poorer quality of sleep.^1,2,8

More research is needed into establishing if artificial lighting is a risk for myopia and if sleeping late is making children more likely to read or use screens in poor light when they should be sleeping or if they are more susceptible to circadian rhythm disturbance

Although this study found no significant relationship between sleep duration and myopia, one study from Korea¹ found that after adjusting for other risk factors, students who slept more than 9hrs were 41% less likely to have myopia compared to those who slept less than 5hrs. Another study from China found a higher myopia risk if children slept longer every night.⁹

• Further research could explore a link between sleep duration and myopia

There were some limitations to this study:

• The questionnaires gathered data on bedtimes and waking times as recorded by parents.
  • The information provided by parents may be subject to recall bias
  • Although the children had wearable devices, they were removed early evening.
  • Using wearable devices to monitor objectively monitor sleep patterns in further studies will help collaborate questionnaire responses.
• The study was carried out in Shanghai where the children shared ethnicity and culture. The study population study was also young (aged 6 to 9yrs at baseline).
  • Expanding the research to other countries and age ranges will discover if the findings apply for a wider population.

Title: Sleeping late is a risk factor for myopia development amongst school‑aged children in China

Authors: Xiao Nicole Liu, Thomas John Naduvilath, Jingjing Wang, Shuyu Xiong, Xiangui He, Xun Xu, Padmaja R. Sankaridurg

Purpose: Myopia, a leading cause of distance vision impairment, is projected to affect half of the world’s population in 30 years. We analysed the relationship between certain demographic, environmental, and behavioural factors and myopia from a 2-year school-based, prospective trial conducted in Shanghai, China.

[Link to open access paper]