For a double eyelid, a single eyelid this situation, there may be two reasons: 1, genetic decision, this is due to the development of one side of the double eyelid development, the other side may be due to some reason, genetic decision, not fully developed, so at birth is a double and a single. In this case, you can perform plastic surgery on the single eyelid after adulthood according to the side of the double eyelid, so that you can do both sides of the double eyelid. 2, it is possible that both sides of the double eyelid at the beginning, but due to one side of the lesion, muscle or skin laxity leads to skin sagging, double eyelid cover, can also result in the situation of a single eyelid and a double eyelid. For this reason, we should go to ophthalmology or plastic surgery department as soon as possible to find out the reason, according to the cause of the situation of the single eyelid side of the rectification surgery, rectification surgery is also against the double eyelid side, to achieve symmetry of the two sides, beautiful, you can make both sides become double eyelids.