Extraocular Muscles

We're in the midst of a short session learning about the eye. For the most part it's fairly interesting and understandable, but I'm beating my head against the wall trying to understand extraocular muscles' functions. The four straight ones (the rectus mucles) are pretty obvious, but the oblique ones are horribly confusing. I've found about half a dozen different sources each telling me a they have a different function.

I think I know which sources are right - and even why the other sources say what they do (mostly a confusion between the function of the muscles, what happens when they're damaged, and how to test them), but wow, that was a lot of searching to get a relatively simple answer.