I've been tinkering with Gen6 lately, and while I'm grateful that Daz brought back the built-in eye surface MAT group, I'm having an issue with my Fresnel shaders, which have always worked before.

I transmap the Cornea to fade out on its edge for smoother-looking eyes.

Whenever I apply anything involving refraction, I get an outer ring on the iris that is the color it should be, while all the rest of the iris/pupil is severely darkened.  I've tried tinkering with the Ray Bias and dialing back the Cornea Bulge morph, but nothing appears to be working.  No matter what, even if I strip the shader down to just a Refract node plugged into the Refraction channel, I get the Ring of Mystery.  Both eyes have shadow casting disabled, so that can't be the problem.

Any ideas will be greatly appreciated.  Thanks in advance!

Units: feet
Ray Bias: 0.004
IOR: 1.38
Shadow Min Bias (on all lights): 0.08