Myopia can be caused by a variety of factors. Two of the most commonly accepted views are that certain factors lead to a lengthening of the eye axis or an increase in the refractive index of the refractive medium, resulting in myopia. In general, the lengthening of the eye axis is associated with an increase in close work, a decrease in outdoor sports, and ageing. The lengthening of the eye axis causes the focal point of the eye to look at distant objects to gradually move forward, and if it falls in front of the retina, it reaches a certain level of myopia, that is, the focal point of distant objects does not fall on the retina but in front of the retina, so that the eye does not see distant objects clearly, resulting in myopic blurring. The same is true for the increase in refractive index, which strengthens the convergence of light and shifts the focus forward, resulting in refractive myopia.