When you get used to seeing Japanese people, you quickly realize there is a very wide variety in facial features here, but it is interesting that it is often categorized in one of these two types. The eyes are pretty distinctive after you start to notice that. Those with a single-eyelid often have the eye opening so narrow that they have to have surgery to make it open a little wider to help them see better as they age. I had a student just a few weeks ago who had that.