Double eyelids refer to a specific eyelid structure where a visible crease forms in the upper eyelid. This crease creates a distinct separation between the eyelid and the brow, giving the eyes a more open and defined appearance. Double eyelids are common in many populations, particularly among individuals of European descent. In contrast, single eyelids lack this crease, resulting in a smoother eyelid surface. The presence or absence of double eyelids can influence beauty standards in various cultures, leading some individuals to seek cosmetic procedures, such as blepharoplasty, to create or enhance the eyelid crease.