The causes of myopia are complex, and have many affecting factors, the main factors could be broadly divided into the genetic factor, the environmental factor and the nutrition physical factor.
The genetic factor
　　Based on a large number of survey data, the unanimously conclusion is that high myopia is related with the genetic, but moderate myopia has great differences. The 高度近视的遗传类型，多数调查资料的结论是常染色体隐性遗传，因此父代与子代可以不同时出现近视。genetic types of high myopia, as that of the majority of survey data conclusion is the autosomal recessive genetic, and therefore the father and his offspring can have myopia not at the same time. 遗传又往往受客观环境，即生活条件的影响使之变异，增加了遗传的复杂性。Genetic often subject to objective circumstances, that is to variance with the change of the living conditions, and increases the genetic complexity.
The environmental factor
　　Environmental factors are primarily close operations and the adverse operating environment, this is the most ancient theory, although there are still some controversy so far, the investigation from the large number of domestic and foreign studies, it has been recognized that the genetic and environmental are the main causes of the myopia, and the environmental conditions is determined as the objective factor of the formation of myopia. 但是，在近距离阅读或近距离工作的影响下，为什么能产生近视？However, under the influence of close proximity to read or work, why it causes short-sighted? 对此还没有一致认识，主要有以下几种理论：The awareness has not yet agreed, mainly are the following theories:
　　a. Conditioning theory
　　The vast majority of myopia emerged in the era of youth, because the ability of adjusting eyes of the adolescents is particularly strong, and has a high degree of adapt closeup work and study; it is not so easy to feel fatigue. H但是睫状肌长时间过度紧张，睫状肌会发生疲劳甚至痉挛而出现调节性近视，不及时消除持续发展则可成为不可逆转的真性近视,或通过其他途径影响到眼球轴的延长。HHowever, if the ciliary muscle in the condition of high tension over time, the ciliary muscle would be fatigued and even spasm and cause regulatory myopia, if does not eliminate promptly, let it continue developing would become an irreversible true myopia, or through other means affect the extension of the eyeball axis.
　　b. Convergence theory
　　When we use regulation in closeup work, we need to strengthen the ability of eyes convergence at the same time which can lead to ocular pressure on the eyeball and caused the eyeball axis extended.
　　c. Environment adapting theory
　　The eyeball is small for children, and the majority showed hyperopia, the eyeball could increases to the face up state as the increase of age. 在这一发育过程中近距离阅读过多，眼球为适应这种调节需要而成为近视。In the development process, if close reading too much, the eyeballs needs to become myopic in order to adapt to this regulation.这一学说受到许多反对，但是在发育期可塑性很强，对近视发展具有重要影响已是共 Such a theory has much opposition, but it is in developable, and is consensus and has an important impact on the development of myopia.
No other theory need to be mentioned, only mention again that external factors such as the light, reading posture, contrast, small fuzzy characters, a short distance and reading for a long time can affect the above factors.
Nutrition physical factors
　　Some of the information from the analysis that the lack of trace element chromium, zinc and strontium, and weak constitution may also affect the incidence of myopia, but how could these factors impact the myopia has many arguments.
　　In short, from the above we can see that there are many factors can cause myopia, both external factors and internal physical factors could affected each other, rather than from a single factor.