You haven't said what version of poser you are using. Saying that the image is grainy, I'm guessing you are using Poser 11 and rendering with the default tsettings. The default render engine is Superfly in Poser 11. This is new and some older materials don't work properly in it. And eyes have particular problems with built in reflections adding to real reflections.

Try going to render setting (you can get to these via the render drop down menu or by clicking ctrl-y in windows, and select the firefly tab. You can now go to the automatic settings and try playing with those. See whether this helps, then later on you can start learning about the various render engines and how to get the best from.