In developed countries, macular degeneration, diabetic retinopathy and glaucoma are the main causes of low vision, while in developing countries, cataract and refractive error are the main causes. The causes of low vision also vary greatly among different age groups. In the age group of 0~29 years, congenital eye diseases are the main causes, including congenital ocular structural defects and nystagmus, congenital cataract, macular dystrophy, congenital optic nerve atrophy, albinism, primary retinitis pigmentosa, posterior fibrous hyperplasia, etc. In the age group of 30~59 years, the causes are optic nerve atrophy, primary retinitis pigmentosa, diabetic retinopathy, macular dystrophy, myopia, etc. In people aged 60 years or older, age-related macular degeneration accounted for the majority of cases, reaching more than 50%, followed by glaucoma, senile cataract, diabetic retinopathy, optic nerve atrophy, myopic retinal chorioretinopathy and so on. In terms of the traditional definition of low vision, the primary cause worldwide is cataract, while the main cause of low vision in daily life is refractive error. Our country is a developing country, due to the economic and cultural underdevelopment, as well as the unpopularity of optometric knowledge and the incorrect traditional concept of eyeglasses, a considerable proportion of people of all ages live in a state of low vision due to refractive error or the inability or unwillingness to make refractive correction.