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Introduction
Myopia is a common ocular disorder worldwide. In Caucasians, myopia has a prevalence of approximately 30%-40% in adults. 1 2 It is even more frequent in the Asian populations with a prevalence of 80%-90%. 3 4 In Chinese, the prevalence of myopia has been increasing rapidly. In the generation born in the 1960s, the myopia prevalence was around 10%-20%. Today, it has increased to 80%-90% in teenagers and young adults. 5-7 Individuals with high and extreme myopia are prone to vision-threatening complications. Among high myopes, reportedly 23% had developed posterior staphyloma, 19.3% chorioretinal atrophy, 8 14.8% myopic foveoschisis, 10% choroidal neovascularisation 9 10 and 6.28% macular hole. 11 12 As for retinal detachment, the odds was 7.8 in subjects with myopia. 11 Apart from retinal complications, the risk of glaucoma is higher in high myopic adults. 13 14 Therefore, prevention and treatment of myopia is an important issue of public health.
Myopia is a complex disease resulting from the interaction of multiple environmental and genetic risk factors. Previous studies have identified many associated genetic loci. The paired box gene 6 (PAX6) gene is one of the genes that were associated with myopia. PAX6 is an oculogenesis gene playing an important role in the development of eyeball. 15 Mutations in PAX6 were related to ocular complications including aniridia, presenile cataract, foveal hypoplasia and microphthalmia. 16 PAX6 may also have a role in the change of refractive powers of the cornea and the lens, as well as the elongation of the globe, and thus in myopia development or progression. 15 17
The PAX6 gene was first revealed as a susceptibility gene for high myopia by Hammond et al in 2004. 18 However, subsequent studies in other study cohorts had inconsistent results. Our previous meta-analysis indicated that PAX6 was associated with high or extreme myopia. 19
Of note, previous studies mainly investigated the association of high or extreme myopia with PAX6. In the present study, we evaluated the association of PAX6 single-nucleotide polymorphisms (SNPs) with different severities of myopia, with a view to confirm whether the PAX6 gene is a genetic determinant only for higher grade myopia, or it also has impact on low-grade of myopia. If the former is true, PAX6 could be...