The claims describe managing an avatar display list on the client, such that avatars which are too far from the client's avatar, or too far past the sides of the field of view, fall off the list, and that the client only displays up to a certain number of nearby avatars.
A whole lot of MMO shops use display list clipping because they're a stock way to keep the frame rate up. It is the kind of stuff that has been done in viewing parts of 3D virtual space since the 70s.
I guess the novelty justifying the patent is combining the display list with the client being responsible for deciding what to clip, and with 3D avatars. Looking at the huge number of MMOs out there that do this exact sort of thing, I have to wonder just how novel the basis for the patent really is.
Prior art might be found by studying the code for XTrek, based on Empire for PLATO. If spaceship doesn't fall within the viewport for the universe, don't draw it, and I believe XTrek was client-server, but not 3D.