If the eyes have true reflection nodes attached then you will need an environment to cast actual surrounding reflections.  You might connect the textures to the ambient channel but that defeats realism if that is what you are achieving.  The only time you would really need clarity in the eyes would be for closeups.  Angled lighting and distance will show very little detail.

Scaling can be found on the SSS node in the MatRoom.  Higher values, less translucency, lower values, more.  You do need raytracing for this feature to work adequately.