Jenny M. Ip

Outdoor Activity Reduces the Prevalence of Myopia in Children

OBJECTIVE To assess the relationship of near, midworking distance, and outdoor activities with prevalence of myopia in school-aged children. DESIGN Cross-sectional study of 2 age samples from 51 Sydney schools, selected using a random cluster design. PARTICIPANTS One thousand seven hundred sixty-five 6-year-olds (year 1) and 2367 12-year-olds (year 7) participated in the Sydney Myopia Study from 2003 to 2005. METHODS Children had a comprehensive eye examination, including cycloplegic refraction. Parents and children completed detailed questionnaires on activity. MAIN OUTCOME MEASURES Myopia prevalence and mean spherical equivalent (SE) in relation to patterns of near, midworking distance, and outdoor activities. Myopia was defined as SE refraction < or = -0.5 diopters (D). RESULTS Higher levels of outdoor activity (sport and leisure activities) were associated with more hyperopic refractions and lower myopia prevalence in the 12-year-old students. Students who combined high levels of near work with low levels of outdoor activity had the least hyperopic mean refraction (+0.27 D; 95% confidence interval [CI], 0.02-0.52), whereas students who combined low levels of near work with high levels of outdoor activity had the most hyperopic mean refraction (+0.56 D; 95% CI, 0.38-0.75). Significant protective associations with increased outdoor activity were seen for the lowest (P = 0.04) and middle (P = 0.02) tertiles of near-work activity. The lowest odds ratios for myopia, after adjusting for confounders, were found in groups reporting the highest levels of outdoor activity. There were no associations between indoor sport and myopia. No consistent associations between refraction and measures of activity were seen in the 6-year-old sample. CONCLUSIONS Higher levels of total time spent outdoors, rather than sport per se, were associated with less myopia and a more hyperopic mean refraction, after adjusting for near work, parental myopia, and ethnicity.

Role of near work in myopia: findings in a sample of Australian school children.

PURPOSE To examine the association of time spent in near work and reading with spherical equivalent refraction (SER) in a population-based sample of 12-year-old Australian schoolchildren. METHODS Data on the time spent in near-work or outdoor activities per week and estimates for the duration of continuous reading and reading distances, were collected in questionnaires (2353 participants, 75.3% response) in the Sydney Myopia Study between 2004 and 2005; 2339 children underwent a comprehensive eye examination, including cycloplegia. RESULTS Longer time spent on reading for pleasure and reports of close reading distance (< 30 cm) were associated with a more myopic refraction after adjustment for age, sex, ethnicity, and school type (P(trend) = 0.02 and P = 0.0003, respectively). Time spent in individual near-work activities, however, correlated poorly with SER (all r < or = 0.2) and was not significant in multivariate analyses for myopia (SER < or = -0.50 D), with adjustment for age, sex, ethnicity, parental myopia, school type, and outdoor activity. Children of European Caucasian ethnicity reported spending marginally less time in near work than children of East Asian ethnicity (26.0 h/wk vs. 32.5 h/wk, P < 0.0001). East Asian ethnicity, however, was associated with substantially greater odds of having myopia (odds ratio [OR], 11.0; 95% confidence interval [CI], 7.0-17.4). Near work such as close reading distance (< 30 cm) and continuous reading (> 30 minutes) independently increased the odds of having myopia in this sample of children. CONCLUSIONS Although myopia was not significantly associated with time spent in near work after adjustment for other factors, there were significant independent associations with close reading distance and continuous reading. These associations may indicate that the intensity rather than the total duration of near work is an important factor.

Ethnic differences in refraction and ocular biometry in a population-based sample of 11-15-year-old Australian children

PurposeTo examine the prevalence of refractive error and distribution of ocular biometric parameters among major ethnic groups in a population-based sample of 11–15-year-old Australian children.MethodsThe Sydney Myopia Study examined 2353 students (75.3% response) from a random cluster-sample of 21 secondary schools across Sydney. Examinations included cycloplegic autorefraction, and measures of corneal radius of curvature, anterior chamber depth, and axial length.ResultsParticipants mean age was 12.7 years (range 11.1–14.4); 49.4% were female. Overall, 60.0% of children had European Caucasian ethnicity, 15.0% East Asian, 7.1% Middle Eastern, and 5.5% South Asian. The most frequent refractive error was mild hyperopia (59.4%, 95% confidence interval (CI), 53.2–65.6), defined as spherical equivalent (SE) +0.50 to +1.99 D. Myopia (SE−0.50 D or less) was found in 11.9%, 95% (CI 6.6–17.2), and moderate hyperopia (SE⩾+2.00 D) in 3.5%, 95% (CI 2.8–4.1). Myopia prevalence was lower among European Caucasian children (4.6%, 95% CI 3.1–6.1) and Middle Eastern children (6.1%, 95% CI 1.3–11.0) than among East Asian (39.5%, 95%, CI 25.6–53.5) and South Asian (31.5%, 95%, CI 21.6–41.4) children. European Caucasian children had the most hyperopic mean SE (+0.82 D) and shortest mean axial length (23.23 mm). East Asian children had the most myopic mean SE (−0.69 D) and greatest mean axial length (23.86 mm).ConclusionThe overall myopia prevalence in this sample was lower than in recent similar-aged European Caucasian population samples. East Asian children in our sample had both a higher prevalence of myopia and longer mean axial length.

Myopia and the Urban Environment: Findings in a Sample of 12-Year-Old Australian School Children

PURPOSE To examine associations between myopia and measures of urbanization in a population-based sample of 12-year-old Australian children. METHODS Questionnaire data on sociodemographic and environmental factors including ethnicity, parental education, and time spent in near work and outdoor activities were collected from 2367 children (75.0% response) and their parents. Population density data for the Sydney area were used to construct five urban regions. Myopia was defined as spherical equivalent refraction </= -0.50 D. RESULTS Myopia prevalence was lowest in the outer suburban region (6.9%) and highest in the inner city region (17.8%), with mean refraction tending toward greater myopia by region (outer suburban to inner city), after adjustment for age, sex, ethnicity, near work, outdoor activity, and parental myopia. Multivariate-adjusted analyses confirmed greater odds for myopia in regions of higher population density (P(trend) = 0.0001). Myopia was significantly more prevalent among children living in apartment residences than other housing types (chi(2) < 0.0001), after adjustment for ethnicity, near work, and outdoor activity. Housing density (measured as the number of houses visible from a front door) was not significantly associated with myopia (chi(2) = 0.1). For both European Caucasian and East Asian children, myopia was most prevalent in the inner city region (8.1% and 55.1%, for European Caucasian and East Asian, respectively). CONCLUSIONS The higher myopia prevalence in inner city-urban areas compared with outer suburban areas for this large childhood sample suggest that even moderate environmental differences within a predominantly urban setting may be associated with increased odds of myopia. These findings are consistent with previous reports of rural-urban differences in childhood myopia.

Prevalence and associations of anisometropia and aniso-astigmatism in a population based sample of 6 year old children

Aim: To study the distribution of anisometropia and aniso-astigmatism in young Australian children, together with clinical and ocular biometry relations. Method: The Sydney Myopia Study examined 1765 predominantly 6 year old children from 34 randomly selected Sydney schools during 2003–4. Keratometry, cycloplegic autorefraction, and questionnaire data were collected. Results: Spherical equivalent (SE) anisometropia (⩾1 dioptre) prevalence was 1.6% (95% confidence interval (CI) 1.1% to 2.4%). Aniso-astigmatism (⩾1D) prevalence was 1.0% (CI: 0.6% to 1.6%). Both conditions were significantly more prevalent among moderately hyperopic (SE ⩾2.0D) than mildly hyperopic (SE 0.5–1.9D) children. Myopic children (SE ⩽−0.5D) had higher anisometropia prevalence. Neither condition varied by age, sex, or ethnicity. In multivariate analyses, anisometropia was significantly associated with amblyopia, odds ratio (OR) 29, (CI: 8.7 to 99), exotropia (OR 7.7, CI: 1.2 to 50), and neonatal intensive care unit (NICU) admission (OR 3.6, CI: 1.1 to 12.6). Aniso-astigmatism was significantly associated with amblyopia (OR 8.2, CI: 1.4 to 47), maternal age >35 years (OR 4.0, CI: 1.3 to 11.9), and NICU admission (OR 4.6, CI: 1.2 to 17.2). Anisometropia resulted from relatively large interocular differences in axial length (p<0.0001) and anterior chamber depth (p = 0.0009). Aniso-astigmatism resulted from differences in corneal astigmatism (p<0.0001). Conclusion: In this predominantly 6 year old population, anisometropia and aniso-astigmatism were uncommon, had important birth and biometry associations, and were strongly related to amblyopia and strabismus.

Can Information on the Purpose of Spectacle Use and Age at First Use Predict Refractive Error Type

Purpose: To assess the sensitivity and specificity of predicting refractive error type using information from a four-item questionnaire on the purpose of spectacle use and age at first use. Methods: The Sydney Myopia Study examined 1,740 year 1 (78.9% response) and 2,353 year 7 students (75.3% response) from a random cluster sample of 34 primary and 21 secondary schools across Sydney. Parents of participants completed a four-item questionnaire that sought data on parental spectacle use, age at first use, and purpose of use (for clear distant vision, close work, or both). Prescriptions were obtained for 720 of 3,209 (22%) parents (73% of those approached) for validation. A receiver operating characteristic (ROC) curve was used to determine the optimal cutoff age for spectacle use in myopia classification. Results: Using the ROC curve, a cutoff age of 30 years at first spectacle use produced the highest accuracy in determining myopia. We combined information on the purpose for using spectacles (for distant and near vision) and age of first use at 30 years or younger to determine myopia, otherwise hyperopia. Validated against prescriptions, the sensitivity and specificity of these predictions were 0.89 and 0.83, respectively, for myopia. The specificity was 0.92 for hyperopia and 0.80 for astigmatism, though corresponding sensitivities were lower at 0.23 and 0.46, respectively. Conclusions: In a sample of the parents of Sydney Myopia Study participants, information on the purpose of spectacle use with an age-at-first-use criterion can identify myopic refractive error with reasonable sensitivity and specificity. This four-item questionnaire may assist future epidemiological studies of screening for myopia.