This is a facial characteristic, similar to the color of the face. It is not so important in face reading. They eyes are however a key part of the face reading. What you are looking for is the qi within the eyes. Much is said by the eyes. You can tell if someone is being deceiptful or is very open by the eyes.
Start observing eyes and you will see what I mean.
I have learned that eye shapes do have meaning – for instance – half moon shaped eyes indicate a lot of sadness in one’s life. (Like the actress who played Angela on Who’s the Boss? – I can’t think of her name right now…) “Beady” eyes are someone not to be trusted. Bulging eyes is kind of a wacko.