Eye darts are one of those things that you don't see a ton of in Traditional animation. Why, I'm not sure. I certainly don't believe that it's too subtle for hand drawn-- lotsa people have proved that wrong, but i would say it is much MUCH more difficult to pull off in hand drawn.
More than how you pull it off though is WHY you pull it off. I've never had a director tell me this but i have had friends that have told me some directors will just tell them as they are finishing their shots, "looks great, now throw some eye darts in there and it's done!" OK, but ummmm, why? The funny thing is that when i do it in hand drawn most directors ask me to take them out. Weird--
There are many different feelings about eye darts-- Some people say they weaken the character, some people say without them the character looks dead. You can always go too far in either direction so I lie somewhere in the middle. It's always about the story your telling-- as an animator you tell stories in Micro form, shot by shot. There may be a time when a character is tense and very serious about something. That could be a time to hold those eyes still, like laser focused! Remember ever being yelled at by someone who was dead serious and they lock eyes with you so you know they are not kidding? That's what I'm talking about--
Sometimes though your character might need to be pondering something or reading someones expression. This is where the social triangle comes in. I thought a great way to teach this would be by looking at someone with the body of a greek god, and the face of an angel. It was an easy choice--
OK, soooo-- Social Triangle. It's exemplified below as the the first things we look at on other people to read how they are feeling about us, about themselves, what they are thinking... just reading them in general.
Generally when i do eye darts, especially in conversation bits, I dart them back and forth from left to right. If the character is right handed I start on the other characters right eye and work to the left and back again. If the character is left handed I will do the exact opposite--
The last thing we read on the face is the mouth. So at times i will alternate down slightly in between the left to right motion.
The thing about this stuff is knowing when to use them-- I love qoutes and I'm gonna butcher this one but it's a really neat one my friend Tony DeRosa told me. He said Mark Twain said this about writting, "The difference between finding a good word and the exact word to explain something is like the difference between a firefly and a lightening bolt!" What's that have to do with eye darts? well, eye darts aid in acting, and (an animation as a whole) is about distilling life to it's essence. When you see a good caricature of someone, it might take you a minute to get it then you forget it. But when you see an Al Hirschfield caricature it's like that lightening bolt man! It hits you because he's captured the essence of the person. Acting should capture the essence of the feelings of the moment. Eye Darts are one of the many tools to help you do that. This little post was more just to explain why and how to use them-- hope it helps!