Bailey
A Fixture
I just wrote an article discussing my approach to painting eyes. This details how I'd approach the eyes for a bust or 90mm figure, however I use a similar (though simplified) approach for 75 and 54mm figures so it has some suggestions for those too.
You can check out the tutorial here: http://figurementors.com/method-for-painting-eyes-on-busts-and-smaller-scales
You can check out the tutorial here: http://figurementors.com/method-for-painting-eyes-on-busts-and-smaller-scales