The character's eyes are made up of two UV Spheres, the Corneas and the Eyes objects: the bigger Corneas one enveloping a smaller Eyes sphere, which in turn is made up of three parts: the eyeballs, the irises, and the pupils.
The Corneas sphere was first painted with a totally black Vertex Color layer, then painted with a white color only to the vertices corresponding to the front crystalline lens.
The Eyes sphere has three different materials assigned to the three different parts:
Start Blender and open the Gidiosaurus_skin_Cycle_02.blend
file; save it as Gidiosaurus_shaders_Cycles.blend
.
Enable only the 6th and the 12th scene layer, in order to have visible only the Corneas, the Eyes and the Lamp objects (actually the Camera is also on the 6th scene layer, but it's hidden and at the moment we don't need...