Welcome to the world of children's vision!

Introduction

An early study in Australia reported that playing outdoors more could have a link with a lower prevalence of myopia in children was published in 2008 by Kathlyn Rose and colleagues (1) ; this study was impressive with the number of children involved: over 4000 children were included in the “Sydney Myopia study”, which took place between 2003 and 2005.

The authors showed that higher levels of outdoor activity (sports and leisure) were associated with more hyperopic refractions and lower myopia prevalence among students 12 years of age. Students who performed a lot of near work indoor and spent the least time playing outside showed less hyperopia and more myopia. The opposite is also true.

The same research team (2) measured the presence of myopia in two of age- and ethnicity-matched primary school children participated: 124 from the Sydney Myopia Study and 628 from the Singapore Cohort Study on the Risk Factors for Myopia.

The prevalence of myopia in 6- and 7-year-old children of Chinese ethnicity was significantly lower in Sydney (3.3%) than in Singapore (29.1%) (P< .001). The prevalence of myopia in 1 or more parents was 68% in Sydney and 71% in Singapore. Children in Sydney read more books per week (P < .001) and did more total near-work activity (P = .002). Children in Sydney spent more time.

On outdoor activities (13.75 vs 3.05 hours per week; P < .001), which was the most significant factor associated with the differences in the prevalence of myopia between the 2 sites.

They then examined teenage children (3) (1249 participants) in the Singapore Cohort study Of Risk factors for Myopia (SCORM), during 2006.

The mean total time spent on outdoor activity was 3.24 h/day. The total outdoor activity (h/day) was significantly associated with less myopia. In addition, the total time spent outdoors was associated with significantly less myopia. Total sports time was also significantly associated with less myopia, but not indoor sports.

Participants who spent more time outdoors were less likely to be myopic. Thus, outdoor activity may protect against development of myopia in children, supporting recent Australian data (see above).

Other studies have followed thereafter and future research will surely come.

Other studies

In 2010, Deng (4) investigated the association of children’s refractive errors with their visual activities assessed by questionnaire in the school year and summer break (June, July, and August).

During the school year, myopes spent significantly fewer hours (8.25 ± 6.24 h/week) than non-myopes (10.95 ± 5.95 h/week) in sports/outdoor activity (p < 0.05). In addition, myopes (12.78 ± 9.28 h/week) watched more television than non-myopes (8.91 ± 5.95 h/week) (p = 0.02). No significant refractive group differences were found for other activities.

A new finding is the high number of sports/outdoor activity hours for both myopes and non-myopes during the summer break, which may contribute to slowed eye growth in all children during these 3 months.

Guggenheim (5)  followed participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) who were assessed at ages 7, 10, 11, 12, and 15 years, and classified as myopic (≤-1 diopters) or non myopic.  Physical activity at age 11 years was measured objectively using an accelerometer, worn for 1 week. Time spent outdoors was assessed via a parental questionnaire administered when children were aged 8-9 years.

Time spent outdoors was predictive of incident myopia independently of physical activity level. The greater association observed for time outdoors suggests that the previously reported link between “sports/outdoor activity” and incident myopia is due mainly to time outdoors rather than physical activity.

Dharani et al. (6) analyzed the time spent outside in, using a log notes and a light meter over a period of 1 week in Singapore for 117 children aged 6-12 with and without myopia. All children wore the light meter for 1 week and parents completed the log outdoor activities for children for 7 days.

The agreement between the light meter measures and the activity logbook was poor to fair. Both instruments measure different parameters, without doubt, time spent outside and the light intensity that results, and it does not seem a useful approach to understand the different aspects of risk in future studies for myopia.

Donovan (7) has analysed seasonal variations in the myopic progression of Chinese children.

They examined a total of 85 Chinese children with myopia between -0.75 D and -3.50 D and astigmatism ≤ -1.50 D, who wore glasses to see far away. They measured refraction and the axial length of the eye at 6 month intervals. The growth rate of the right eye was defined for the first and second 6 months of the study and classified according to “summer”, “autumn”, “winter” or “spring.”

The average increase of 6 months was -0.31 ± 0.25 D for the summer, -0.40 ± 0.27 D for the fall, -0.53 ± 0.29 D for the winter, and -0.42 ± 0.20 D in the spring (p <0.001). The increase in axial length was 0.17 ± 0.10 mm for the summer, 0.24 ± 0.09 mm for autumn, 0.24 ± 0.09 mm for the winter, and 0.15 ± 0.08 mm for the spring (p <0.001). In addition, data for summer and winter were different from each other for the progression of myopia and axial elongation.

Myopia progression in summer months was approximately 60% of that seen in winter, and axial elongation was likewise significantly less in summer. It is unclear whether more time spent outdoors in summer vs. winter is a contributing factor, or the difference in progression rates is a result of “seasonal” variations in the intensity or amount of close work performed.

Jones-Jordan (8) has also investigated the association between myopia progression and time spent outdoors and in various visual activities.

Their results indicate that the number of hours of reading for pleasure per week was not significantly associated with annual myopia progression, nor were the other near activities. The magnitude of effects was clinically small.

Despite previous associations between time spent outdoors and the risk of developing myopia, these authors were unable to obtain the same results …

Conclusion:

One of the surprises of recent research is the importance of how the increased time spent outdoors helps prevent myopia. At present, it seems that 14 hours per week or more outside are significantly effective in reducing the progression of myopia.

Why this surprising relationship? Here are some suggestions:

• Exposure to sunlight increases the production of vitamin D (vitamin D is produced by the skin, using sunlight)? But a study showed that blood concentrations of this vitamin is not significantly different in children who spend more time outdoors than others…

• Exposure to sunlight increases the production of chemicals in the retina such as dopamine which controls the growth of the eye?

• Children often look away when they play outside?

• Exposure to beneficial microorganisms (production of serotonin, which is part of the signaling system in the retina of the eye to counter the growth of the eye)?

We know it is not sports and physical activities are involved. The benefits are possible for the children to play outside without organized sport activity.

References:

(1) Rose KA, Morgan IG, Ip J, Kifley A, Huynh S, Smith W, Mitchell P.Outdoor activity reduces the prevalence of myopia in children. Ophthalmology. 2008 Aug;115(8):1279-85.

(2) Rose KA, Morgan IG, Smith W, Burlutsky G, Mitchell P, Saw SM. Myopia, lifestyle, and schooling in students of Chinese ethnicity in Singapore and Sydney. Arch Ophthalmol. 2008 Apr;126(4):527-30.

(3) Br J Ophthalmol. 2009 Aug;93(8):997-1000. Epub 2009 Feb 11. Outdoor activity and myopia in Singapore teenage children. Dirani M, Tong L, Gazzard G, Zhang X, Chia A, Young TL, Rose KA, Mitchell P, Saw SM.

(4) Deng L, Gwiazda J, Thorn F. Children’s refractions and visual activities in the school year and summer. Optom Vis Sci. 2010 Jun;87(6):406-13.

(5) Mutti DO, Marks AR. Blood levels of vitamin D in teens and young adults with myopia. Optom Vis Sci. 2011 Mar;88(3):377-82.

(6) Dharani R, Lee CF, Theng ZX, Drury VB, Ngo C, Sandar M, Wong TY, Finkelstein EA, Saw SM. Comparison of measurements of time outdoors and light levels as risk factors for myopia in young Singapore children. Eye (Lond). 2012 Jul;26(7):911-8. doi

(7) Donovan, L, Sankaridurg, P, Ho, A. Chen, X. Lin, Z. Thomas, V. Smith, E L. III, Ge, J. Holden, B. Myopia Progression in Chinese Children is Slower in Summer Than in Winter.  Optometry & Vision Science. 89(8):1196-1202, August 2012.

(8) Jones-Jordan LA, Sinnott LT, Cotter SA, Kleinstein RN, Manny RE, Mutti DO, Twelker JD, Zadnik K; for the CLEERE Study Group.Time Outdoors, Visual Activity, and Myopia Progression in Juvenile-Onset Myopes. Invest Ophthalmol Vis Sci. 2012 Oct 15;53(11):7169-7175.

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