The double eyelids gene for autosomal dominant, only for the recessive. The single also double have parents genetically determined, the double-fold eyelid by dominant gene control, namely the genotype AA or Aa decided the double-fold eyelid; single eyelids by recessive gene control,namely the genotype AA decided single eyelids. Single eyelids, eyelid is produced with the upper eyelid levator muscle in a relationship. The double-fold eyelid formation as a result of the levator muscle fibers extending to the subcutaneous tissue, muscle contraction caused by attachment of skin retraction, constitute the skin folds, namely double blepharoplasty, commonly known as eyelid; single eyelids is this lack of attachment to the skin of the levator palpebrae superioris muscle fibers, so there is no plica. If an individual's genotype containing control double-fold of the dominant gene A, his characters in general should be a double-fold eyelid. But during ontogeny, due to other genetic modification or internal, external environment factors, may lead to the levator palpebrae superioris muscle fiber development is incomplete, it may lead to some eyes are a single fold, the other eye is double-fold eyelid; others exhibit a stage show the double-fold eyelid, a stage show and single eyelids.