Everybody else thinks you mean the standard OCaml top-level. However, ocaml-top is a gtk-based editor for editing and evaluating OCaml code: http://www.typerex.org/ocaml-top.html
I just installed it on my OS X Maverics system, which was really quite difficult. You say you have it installed already. If so, that's impressive as I really found it difficult :-)
Now that I have it installed, I can run it by saying:
$ ocaml-top
In the Terminal (the command line). It looks pretty good, and it does let me edit and execute OCaml code. I've only tried a few simple things.
However, ocaml-top uses X11 to display its windows. So, you also need to have X11 installed on your OS X system.