Raytrace and Lenses
 

I've modeled a dispersing lens and placed it over a hole in a piece of geometry. I've places a light on one side to create some sort of a flashlight...
Problem is, even though I turned raytracing and raytrace shadows on, and gave the lens a refractive index of 1.5(glass) it doesn't effect the shadows on the other side - I get exactly the same shadows with 1 and 1.5 refractive indexes.

Does someone know what I need to do to get a more realistic raytracing?
Thanks in advance,
Benny

Here's a pic of the lens
http://img523.imageshack.us/img523/6973/tempsq1.jpg

Can global illumination help me with this? I tried turning it on and got some really weird results... If so, can someone please post some tutorials about it?
Thanks in advance,
Benny