well it kinda' like a fold in the lower part of your eyes, which if you don't have eyebags will look like a line. most of the koreans or even some japanese don't have this kind of fold or line under them. so what they do is augment the lower part of their eyes by surgery so that they will have this line. hope im clear with this. its alot easier to understand if i can show you some pics but can't find anything suitable for an example. hope you understand

for me its just fine if you just have a single fold.

maybe konnichiwa-san can explain it better.