Hello There!

Is there a way to create a kind of spherically symmetric volumetric dielectric shader which will give me a sphere with a spherically symmetric refractive index, i.e. n(r)?
Can one maybe ramp the IOR of a dielectric mr shader?

I am trying to create a certain lens-like effect through this... Any help would be appreciated!

Thanks,

Markus 

does the lens have to be perfectly spherical?

yes, it should be perfectly spherically symmetric...

working a year on it now..? If mr is a simulation of physically correct lighting, this what you want shouldnt be possible in your way.  Ray directions change on passing borders of different transparent substances, so from glas to water or water to air and so on. Inside a medium the IOR is constant (otherwise rays would be redirected from atom to atom and you should be fine with sub surface scattering), so all what you want to achive should be done at your spheres surface. Maybe you go a bit more into detail whats the goal.