Sir,

We thank Zayats et al for their comments and interests in our recently published article.1 They were concerned with the different effect of PAX6 polymorphism in myopia between Taiwan and Europe, the reason of lack of association with high myopia, and the risk of a Type I error in our study. We would like to reply their comments as follows.

More and more evidences support that myopia is caused by both genetic and environmental factors and possibly their interactions.2 Besides the interactions with environment, owing to multiple genes with small effects, genetic heterogeneity and phenotypic complexity, the study of the genetics of myopia poses a complex challenge and may obtain different results in different countries. Hence, the effects of PAX6 polymorphisms in myopia are likely to be different between Taiwan and Europe because of different environment and race.

Prolonged near visual tasks is an important environmental influence in myopia in Taiwan: individuals with higher education have a higher prevalence of myopia than people in the general population.3, 4 However, among the students in the same class of the same university, who were previously performing similar near visual tasks, their severity of myopia varied widely. For example, the first-year medical students in our China Medical University, although most of them are among mild-to-high myopia, there are extreme myopia. Because they did similar near visual tasks, we assume that their near works resulted in mild-to-high myopia, and there were genes predisposing some students to develop high-to-extreme myopia. Hence, the lack association of PAX6 with high myopia in our study may be due to the distinction in genetic risk factors for high and extreme myopia, or part of high myopia students are caused by their near works only, which is not related to PAX6 polymorphism, suggesting that high myopia can be caused by genetic or environmental factors separately or through their interactions.

The maximum chance of making a Type I error is denoted by alpha. Because our P-values are either 0.002 or less than 0.001, the probability of making a Type I error is low.