This eye material is a bit of an experimentation to see if I could get a performant, flexible, and appealing eye working with only a standard sphere and some math, instead of the layered approach in either geometry or multiple passes shading.
I displace the cornea, calculate approximate corneal bulge normals, place the iris surface at an approximate location via distortion, and provide parameters to control the visual properties.
I wanted this to be flexible enough to use across many types of characters, and to have some of the features useful for certain types of stylized animation and reactions.