Myopization factors affecting urban elementary school students in Taiwan

To investigate factors that may contribute to the myopization of urban elementary school students in Taiwan.

Grades 1 to 6 students of the same racial background (n = 1894; mean age, 6.3-11.3 years) in three schools, located in Tamsui, Taichung, and Tainan, were refracted to obtain the best corrected visual acuity. The refractive power needed for best corrected visual acuity was used for subsequent statistical analysis. On behalf of their children, parents also completed a questionnaire on six categories of potential myopization variables. Correlation between these variables and the increase or decrease in the refractive error was assessed. The predictive value of each variable was also calculated based on linear regression analysis.

The overall mean refractive error in grades 1 to 6 was -0.37, -0.68, -1.33, -1.60, -1.90, and -2.51 D, respectively. The prevalence of myopia (-1.00 D or more minus) showed a significant difference between grades 2 and 3 and, again, between grades 5 and 6. In addition, 20 potential modulating factors were evaluated; 65.9% of the change in the refractive error could be explained by four: (1) lag in optimal correction, defined as a -1.00-D deficit between new refractive error and current optical correction; (2) outdoor spectacle wear; (3) spectacles for different working distances; and (4) hours spent on reading and writing on weekdays. In contrast, outdoor time and the intake frequency of 36 food items both held very low predictive values of 0.2% and 2.5%, respectively.

Each variable associated with the refractive error has a different predictive value, either positive or negative. Ultimately, the interplay of these variables decides the outcome of the pattern and the degree of school myopia.