Table 3.
Studies excluded from meta‐analysis and dose–response analysis
| Study (first author, year) | Participants [region] | Outcomes | Reasons for exclusion | Total score (percentage) | Quality |
|---|---|---|---|---|---|
| Myopia Incidence – Cohort Study | |||||
| Zadnik et al. (2015) | 4512 schoolchildren enrolled in CLEERE study; age: 6 through 13 years. [USA] | Time outdoors was not associated with risk of myopia onset in multivariate models (data not shown). | Data from multivariate model were not available | 9 (60%) | Medium |
| Jones‐Jordan et al. (2011) | 731 incident myopes and 587 emmetropes in the CLEERE study. [USA] | Hours per week spent in outdoor/sports activities were significantly less for children who became myopic 3 years before onset through 4 years after onset by 1.1–1.8 hr/week. | No multivariate OR or RR was presented. | 9 (60%) | Medium |
| Onal et al. (2007) | 207 Turkish medical students; mean age: 21.11 ± 1.58 years (range: 18 to 26 years); follow‐up for 1 year. [Turkey] | Nonmyopes reported a significantly higher prevalence of outdoor activity before and at age seven (68.4%) than did myopes (48.6%; p < 0.009). Outdoor activity during early childhood was found to be protective for myopia on multivariate analysis (OR = 0.44, 95% CI = 0.23 to 0.82). | Activity was measured as mostly indoor activities or mostly outdoor activities, but not a continuous variable. | 11 (73.3%) | High |
| Peckham et al. (1977) | 383 children aged 7–11 years from a birth cohort. [UK] | Children with myopia participated in outdoor sports as often as those without. | No multivariable OR was available. | 4 (26.7%) | Low |
| Myopia Prevalence – Cross‐sectional Study | |||||
| Saxena et al. (2015) | 9884 schoolchildren; mean age: 11.6 years. [Delhi, India] | An inverse association with outdoor activities/playing was observed with children playing >14 hr in a week (OR = 0.2, 95% CI = 0.14 to 0.26). | Exposure (outdoor activity) was measured as a categorical variable. | 10 (83.3%) | High |
| Ramessur et al. (2015) | 64 monozygotic (MZ) twin pairs discordant for refractive error; mean age: 56 (range 30 to 79 years)14 | The twins who spent more time outdoors (mean score for children aged <16 years, 0.09; 95% CI = 0.03 to 0.15; mean score for children aged 16–25 years, 0.28; 95% CI = 0.15 to 0.41) or performed more outdoors sports (mean score for children aged <16 years, 0.13; 95% CI = 0.04 to 0.21; mean score for children aged 16 – 25 years, 0.23, 95% CI = 0.10 to 0.36) were less likely to be myopic than their twin. | Difference in time spent outdoors between twins was analysed in relation to spherical equivalent discordancy. | 8 (66.7%) | Medium |
| Wen et al. (2015) | 1218 schoolchildren; grade 1 through grade 6 [Sanya, China] | Nonmyopes spent more time outdoors than myopes (7.25 ± 5.35 versus 11.86 ± 6.65 hr/week), although the association was not statistically significant in multivariable regression analysis (<10 hr/week: β = 0.297, SE = 0.125, p = 0.035; >10.0 hr/week: β = 0.365, SE = 0.198, p = 0.073). | No multivariate OR or RR was presented. | 3 (25%) | Low |
| Han et al. (2014) | 2209 schoolchildren; age: 11–15 years. [Qinghai, China] | Outdoor activities per week were associated with myopia (<7 hr/week versus ≥7 hr/week: OR = 1.977, SE = 0.439). | Exposure (outdoor activity) was measured as a categorical variable. | 7 (58.3%) | Medium |
| Lin et al. (2014) | 370 children from primary (age: 6 to 12 years) and secondary (age: 13 to 17 years) [Beijing, China] | A significant association between outdoor activity time and the children's spherical equivalent was found in the primary school students (β = 0.27, p = 0.03) but not in the secondary school students (β = 0.04, p = 0.70). | The association between outdoor activity time and the spherical equivalent but not the prevalence of myopia was estimated. | 10 (83.3%) | High |
| Read et al. (2014) | 102 children (41 myopes and 61 emmetropes) age: 10 to 15 years. [Australia] | The amount of daily time spent in outdoor bright light conditions (>1000 lux) was significantly greater in emmetropes (127 ± 51 min) compared with myopes (91 ± 44 min, p < 0.001) | No multivariate OR or RR was presented. | 7 (58.3%) | Medium |
| Cheng et al. (2013) | 1894 children of grade 1 through grade 6. [Taiwan] | No difference in the time spent outdoors was noted between myopes and nonmyopes. Based on linear regression analysis, weekly daily outdoor activities with sunlight exposure can only predict 0.2% of its extent of association with the refractive error. | The association between outdoor activity time and the spherical equivalent but not the prevalence of myopia was estimated. | 9 (75%) | High |
| Xie et al. (2013) | 929 freshmen who have normal vision when they graduated from primary school. [China] | The prevalence of myopia among students engaging mostly in outdoor activities after class was significantly lower than those engaging mostly in homework (OR = 0.547, SE = −0.140). | The prevalence of myopia was compared between three different kinds of activities including doing homework, playing outdoors and watching TV after class. | 8 (66.7%) | Medium |
| Sherwin et al. (2012) | 636 permanent residents aged ≥15 years from Norfolk Island. [Australia] | UVAF was independently associated with myopia: OR for total UVAF (per 10 mm2) was 0.81, 95% CI = 0.69 to 0.94, p = 0.007. Time spent outdoors was not significantly associated with myopia in the same multivariable model. | The area of UVAF was measured to estimate time spent outdoors. And the amount of time spent outdoors was not measured as hours, but estimated as the proportion of the day. | 10 (83.3%) | High |
| Wu et al. (2010) | 145 schoolchildren; age: 6–12 years. [Taiwan] | Outdoor activity was significantly associated with decreased risk of myopia (adjusted OR = 0.3, 95% CI = 0.1 to 0.9). | Exposure (outdoor activity) was measured as a categorical variable. | 9 (75%) | High |
| Zhang et al. (2010) | 2480 participants with refractive and questionnaire data were included in the final analysis, with a mean age of 13.8 ± 1.1 years. [China] | In multivariable model, outdoor activities were not associated with SER (β = −0.004, 95% CI = −0.019 to 0.011, p = 0.61). | The association between outdoor activity time and the spherical equivalent but not the prevalence of myopia was estimated. | 10 (83.3%) | High |
| Ma et al. (2010)61 | 1363 students; age: 13–18 years. [Zhejiang, China] | Outdoor activity during weekdays was associated with an increased odd of emmetropia relative to myopia (OR 1.145; 95% CI 1.047 to 1.252, p = 0.003). | Data from multivariate model were not available | 8 (66.7%) | Medium |
| Rose et al. (2008a) | 1765 year 1 schoolchildren and 2367 year 7 schoolchildren participated in the Sydney Myopia Study; mean age: 6.7 years for year 1 participants and 12.7 years for year 7 participants. [Sydney, China] | After adjustment for gender, ethnicity, parental myopia, near work, maternal and parental education and maternal employment, a greater number of hours spent outdoors was associated with a more hyperopic mean SER in both year 1 (p < 0.009) and year 7 (p < 0.0003) students. | The association between outdoor activity time and the spherical equivalent but not the prevalence of myopia was estimated. | 10 (83.3%) | High |
| Rose et al. (2008b) | Two cross‐sectional samples 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. [Sydney and Singapore] | Children in Sydney spent more time on outdoor activities (13.75 versus 3.05 hr/week; p < 0.001), which was the most significant factor associated with the differences in the prevalence of myopia between the two sites. | No multivariate OR or RR was presented. | 10 (83.3%) | High |
| Saw et al. (2002) | 957 Chinese schoolchildren aged 7 to 9 years in Singapore and Xiamen, China. [Singapore and Xiamen, China] | Myopic children spent less time on outdoor activities (p = 0.03). No association between outdoor activity and myopia or high myopia, after adjustment (estimate of association not available) was seen. | No multivariate OR or RR estimating the association between outdoor activity and myopia was presented. | 7 (58.3%) | Medium |
| Saw et al. (2001) | Children aged 8–9 years attending second grade from one school in Xiamen city (n = 119) and one school in the Xiamen countryside (n = 91) were recruited. [Xiamen, China] | Myopes spent less time outdoors than nonmyopes (8.9 hr/week for myopia versus 9.8 hr/week for nonmyopia), although not statistically significant (p = 0.12). | Did not provide a measure of association for outdoor activity as a risk factor for myopia that adjusted for potential confounders. | 6 (50%) | Medium |
| Tan et al. (2000) | 414 kindergarten children aged 4 to 6 years. [Singapore] | Children with <7 hr of outdoor activity per week had a higher prevalence of myopia, although this was not statistically significant (RR = 0.81; 95% CI = 0.50 to 1.32). | Univariable analysis was available, but without multivariable analysis. | 7 (58.3%) | Medium |
| Myopia Shift – Cohort Study | |||||
| Wu et al. (2015) | 5052 schoolchildren; age: 6 through 12 years; follow‐up for one year. [Beijing, China] | Significant myopic shift (the change in SER ≤ −0.50D) was independently associated with longer time outdoors for leisure (OR = 0.87, 95% CI = 0.78 to 0.97, p < 0.013) | Myopic shift in refraction in the whole sample but not in the baseline myopes was analysed. | 13 (86.7%) | High |
| Scheiman et al. (2014) | 469 myopic children with SER between −1.25 and −4.50 D; age: 6–11 years; follow‐up for 6–11 years. [USA] | The Gompertz function was used to define the myopia stabilization of each individual. No association between baseline outdoor activities and stabilization by age 15 was observed whether outdoor activity was considered as a categorical or a continuous variable (as a categorical variable: OR = 0.93, 95% CI = 0.53 to 1.65; as a continuous variable: OR = 1.02, 95% CI = 0.99 to 1.06). | Myopia for each child was categorized as stable/not stable by the age of 15 years. Changes in refraction were not analysed in relation to time spent in outdoor activities. | 11 (73.3%) | High |
| Parssinen et al. (2014) | 240 myopic children; mean age at baseline was 10.9, ranging from 8.7 to 12.8 years; follow‐up for 23 years. [Finland] | Myopia increased faster among those who spent 0.5–3 hr on outdoor activities than those who spent >3 hr (p = 0.012). | Trend was demonstrated in a figure. No absolute value of mean differences was presented. | 11 (73.3%) | High |
| Guo et al. (2013) | 681 schoolchildren; the mean age of the children was 7.7 ± 1.6 (ranging 5–13) years; follow‐up for one year. [Beijing, China] | An increase in the SER was significantly associated with less time spent outdoors for leisure (p = 0.006; β = −0.10). | Myopic shift in refraction in the whole sample but not in the baseline myopes was analysed. | 10 (66.7%) | Medium |
| Parssinen & Lyyra (1993) | 240 myopic children; age: 10.9 years; follow‐up for three years. [Finland] | The amount of time spent outdoors was significantly connected with myopic progression in boys (β = 0.23; SE = 0.09; p < 0.01), but not in girls. | The correlation was analysed for boys and girls separately. | 8 (53.3%) | Medium |
CLEERE = Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study, UVAF = ultraviolet autofluorescence, SER = spherical equivalent refraction.