Most Asian groups (and some African) have what is called an “epicanthic fold”.  This is commonly called a “single eye lid” (or derogatory “slanted eyes”), but should be thought of a lack of crease in the eyelid (as in both cases there is only 1 eyelid).  This is usually caused in a lower rooted nasal bridge.  The lack of a crease will lead to a smaller opening for an eye, and eye lashes will generally not curl up or down.  Since larger eyes and curled eyelashes are generally seen as a sign of beauty, many Asians opt to have a crease placed in the middle of the eyelid to truly open up the eyes.