The large difference in refractive error before and after dilation occurs mainly in children with high accommodation ability, after dilation paralyzes the ciliary muscle and relaxes the eye’s adjustment function, resulting in the difference. Because of the strong adjustment of the lens in children, the judgment of true and false myopia will be affected, therefore, children’s vision measurement generally need to be dilated optometry, to exclude the interference of the adjustment ability of the vision test, the refractive error measured is accurate, and this myopia state is called true myopia. The refractive error may be higher in children without dilated pupils, but some of the refractive error may disappear after dilation, which is called pseudomyopia. Pseudomyopia can be restored by adjusting eye habits and proper visual training, while true myopia cannot be restored.