Hi Steven, I don't know how he does his but I'll share how I do mine. Eyes are super important, in my opinion! First I use a very, very pale blue to paint the eyeball. Next the color, for example, if I'm painting a blue eyed person, I will paint the eye color on, using a darker blue than I want the finished eye to be and making sure not to do too 'round' a shape at top and or bottom, that gives the 'startled look'. Next I will mix white or light blue to make a lighter color, thin it down with water and make a little half moon shape at the bottom of the eye. Don't take this lighter color out to the edges, you want to have a ring of darker blue on the outside edge.
By making it a half moon, at the bottom of the eye, it will give a shadowed look at the top, which is what you want. Next paint the pupil in black, again, making sure it's not just a round shape in the middle, part of it should look like it's under the lid.
Then I put a tiny, tiny dot of white in the same spot on each eye. Next I use what Hi Ho mentioned, the Treasure Crystal Cote, I wouldn't do eyes without it now that I've used it, it 'makes' the eyes. If the eye is large enough, I put a coat of it over the entire eye ball, when it dries I add another coat just to the iris, to make it more domed looking.
Hope this helps, good luck!

Callynne