Let us use This texture for our model. Let us make one more shader : surface shader and assign that shader to blocker object.

Now make one more blinn shader for eye object. Make color white, eccentricity 0.1, relectivity 0.2, specular rolloff 0.84. For transparency and make Ramp texture and make it U ramp. Make the lower part black and the upper one white. That will make back part of eyeball opaque and front part transparent and make our iris visible. Use ipr render to make right adjustments to ramp which would look similar to the image shown below.

Now lets add some lights and reflecting objects. Create one directional light with raytrace shadows. And create simple planes for bottom, back and side, similar to walls so that eye can reflect. Switch to mental ray and turn on Final Gathering option. Now make a test render, and the image would similar to the one shown below.

I hope the eyeball image some what perfect. But we still need to make some changes and before that lets analyse what we created and what needs to be fixed.