... study. In summary, our results indicate that an increase in studying intensities could lead to increases in myopia and astigmatism occurrences, but it is not clear whether the occurrence increases ... kilometers, accounting for 71% of the area in main-land China), and includes eleven provinces and one municipality, but the population is relatively sparse (360 million, accounting for only 28% ... being ranked middle in Western China and most residents in this district being Han Chinese. In this study, clusters were defined by geo-graphical residential areas, called residence adminis-trative...