Shanghai Child and Adolescent Large-scale Eye Study -High Myopia Registration

1. introduction 1.1 Overview of myopia and high myopia Myopia is the most common eye disease in the world . Among them, the incidence and prevalence of myopia are highest in developed countries and regions in East and Southeast Asia. It is predicted that by 2050, global myopia patients would reach 5 billion, 1 billion of which were high myopia. In developed countries and regions in East and Southeast Asia, the prevalence of myopia in high school graduates is as high as 80% to 90%. A study in Taiwan showed that more than 80% of adolescents suffered from myopia when they graduated from high school, 10% of whom were high myopia. Another study which focused on university students in Shanghai showed that 95.5% of college students suffered from myopia, and 19.5% of them were high myopia. In stark contrast, the prevalence of myopia in the same age in western developed countries is between 20% and 40%. In less developed countries and regions of the world, the incidence of myopia in young people is about 5% to 10% due to the low level of education.

At present, the etiology and pathogenesis of myopia and high myopia are still unclear. Environmental and genetic factors are involved in the development of myopia and high myopia. Among them, the level of education and outdoor activity time are closely related to the development of myopia and high myopia. At present, most studies believe that the higher the education level, the higher the incidence of myopia and the deeper the degree of myopia. In addition, most studies suggest that outdoor activities was a protective factor for myopia, and increasing outdoor activity time could reduce the incidence of myopia. Also, some studies have shown that the age of onset of myopia was closely related to high myopia. Furthermore, genes may also be closely related to the occurrence of myopia and high myopia. At least 19 myopic loci have been identified through family studies and twin studies till now. With the completion of the Human Genome Project, genome-wide association analysis technology is becoming more and more mature, and more and more related genes and mutation sites have been elucidated, but the pathogenic genes of myopia are still not completely clear. In addition, the genes related to pathological myopia and fundus lesions are currently unclear. In recent studies, high myopia and pathological myopia are not strictly differentiated (pathological myopia is defined by diopter or axial length alone). Therefore, genes related to pathological myopia need further research, in order to judge whether high myopia and pathological myopia are two different diseases at genetic level or different states controlled by the same genes.

1.2 Relationship between high myopia and pathological myopia The fundus of patients with high myopia is often accompanied by a series of pathological changes, such as posterior scleral staphyloma, retinal choroidal atrophy, lacquer crack, choroidal neovascularization（CNV）, macular hemorrhage, Fuchs plaque, retinal palpebral fissure, retinal tear, retinal detachment. These pathological changes are important causes of decreased vision and even blindness. Some studies have shown that macular degeneration caused by myopia has become a major cause of blindness and low vision. In Jing'an District of Shanghai, high myopia with macular degeneration has leapt to the first place in adult blindness. A study in Beijing showed that pathological myopia has become the leading cause of blindness and visual impairment in the 40-49 age group.

Although high myopia is closely related to pathological myopia, and most patients with pathological myopia are highly myopic, high myopia is not equivalent to pathological myopia. The change of diopter and axial length do not fully reflect the characteristics of pathological myopia. Some patients with high myopia have no definite fundus lesions, and some non-high myopia patients may also have posterior scleral staphyloma, retinochoroid atrophy and other complications. At present, Ohno-Matsui K et al define pathological myopia as: myopic macular degeneration ≥ 2 (diffuse retinochoroid atrophy), or additional lesions (lacquer cracks, choroidal neovascularization, Fuchs plaque), or posterior scleral staphyloma. In this definition of pathological myopia, we focus on fundus lesions caused by myopia, and do not emphasize diopter and axial length.

At present, there are still many unknowns about the relationship between high myopia and pathological myopia. The process of developing simple high myopia in children and adolescents as pathological myopia is still unclear. Does high myopia eventually evolve into pathological myopia? Are pathological myopia and high myopia different stages of the same disease or two different diseases? Which fundus changes can predict the occurrence of pathological myopia? These problems need further exploration.