Dr Emily Woodman-Pieterse
PhD BAppSc(Optom) BAppSc(MedSc) GradCertOcTher
School of Optometry and Vision Science, QUT
Associate Professor Scott Read
School of Optometry and Vision Science, QUT
Myopia is widely considered to result from a combination of genetic and environmental influences.1,2 While little can currently be done in regard to one’s genetic susceptibility to myopia, it is possible that modification of environmental contributors may help to control the development and progression of myopia before it advances to pathological levels.
Two of the major environmental factors considered to play a role in myopia include time outdoors and near-work activities. Recent developments in technology to quantify the visual environment and measure ocular parameters have provided novel insights regarding these factors and provide an evidence base for lifestyle modifications to potentially reduce myopia risk.
In recent years, an important role for outdoor activity in myopia has emerged, and while the majority of studies indicate that spending more time outdoors protects against the development of myopia, the exact mechanism underlying these effects is not as clear.3,4
ROAM study results
In the role of outdoor activity in myopia (ROAM) study, our research team utilised wearable sensor technology to examine for the first time the relationship between myopia (and axial eye growth) in childhood and objective measures of ambient light exposure and physical activity, providing new insights into the mechanisms underlying the protective effects of spending more time outdoors.5,6
This study of myopic and emmetropic Brisbane school children revealed no significant differences in the daily physical activity of myopes and emmetropes but did find that myopic children spent significantly less time each day exposed to bright outdoor light levels (Figure 1). This suggests that it is the effect of bright light itself, rather than being active outdoors per se, that appears to impart the protective effect against myopia. Analysis of axial eye growth in this population revealed that irrespective of refractive group, those children who experienced the lowest average daily light exposure had the fastest rate of eye growth (Figure 2).6 Children who spent less than 60 minutes per day exposed to bright light (> 1000 lux) were found to exhibit significantly faster axial eye growth, and therefore were at greater at risk of myopia development and progression. In contrast, children spending on average 120 minutes per day in bright outdoor light levels were found to show slower axial eye growth.
Figure 1. The average daily light exposure of myopic and emmetropic children in the ROAM study, measured with wrist-watch light sensors worn by each child in the study for two 14-day periods. Note the significantly greater light exposure for emmetropic children during the day.5
Figure 2. The average axial eye growth over 18 months for the children in the ROAM study stratified according to their average daily light exposure, irrespective of refractive group. Children habitually exposed to low daily light exposure exhibited significantly faster axial eye growth.6
Near work and myopia
The duration and intensity of near work activities have also often been linked to myopia, with a number of studies finding myopia development associated with greater amounts of near work.7-10 These findings have prompted numerous investigations into the influence of accommodation on ocular parameters. Recent studies from the QUT Contact Lens and Visual Optics Laboratory, utilising highly precise measures of eye length and ocular parameters such as choroidal thickness, have revealed that accommodation results in a small, transient increase in eye length and a thinning of the choroid (Figure 3).11,12
Figure 3. The average change in choroidal thickness (derived from OCT imaging) associated with a 10-minute period of near work (6D accommodation). On average a thinning of the choroid up to ~10 microns was observed.14
Interestingly, in emmetropic eyes, these changes are found to return to normal immediately after the near task is ceased, but in myopes this increased axial length appears to linger following task cessation, taking up to 10 minutes after accommodation is relaxed to return to baseline.12,13 Higher accommodative demands (6D) are accompanied by larger magnitudes of axial elongation,11,14 choroidal thinning14 and anterior scleral thinning15 in the eyes of young adults. This may indicate that in individuals who perform large amounts of intensive near work, particularly those who don’t take sufficient visual breaks, these temporary structural changes will occur more frequently and for longer periods, which may predispose the eye to longer-term structural changes, such as choroidal thinning which is known to be associated with myopia (Figure 4).16
Figure 4. Example of the longer-term changes in choroidal thickness (denoted by red line in OCT scans) associated with myopia. Note the significant thinning of the choroid evident in the 11-year-old myopic child.
These studies provide some theory for evidence-based guidelines to provide to myopic children and their parents regarding lifestyle interventions for myopia control. Children should be encouraged to increase outdoor light exposure to 120 minutes or more per day, regardless of whether this is associated with being physically active. The continued use of sun protection in the form of hats and sunglasses is recommended. In terms of near-work behaviours, because myopic eyes appear to have prolonged recovery times from the ocular effects of intensive near work, frequent visual breaks (a 10-minute break after every 30 minutes of near work) are recommended when performing prolonged near-work tasks.
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14. Woodman-Pieterse EC, Read SA, Collins MJ, Alonso-Caneiro D. Regional changes in choroidal thickness associated with accommodation. Invest Ophthalmol Vis Sci 2015; 56: 6414-6422.
15. Woodman-Pieterse EC, Read SA, Collins MJ, Alonso-Caneiro D. Response of the anterior sclera to accommodation in myopes and emmetropes. Presented at the 15th International Myopia Conference, Wenzhou, China, 2015.
16. Read SA, Collins MJ, Vincent SJ, Alonso-Caneiro D. Choroidal thickness in myopic and nonmyopic children assessed with enhanced depth imaging optical coherence tomography. Invest Ophthalmol Vis Sci 2013; 54: 7578-7586.