I'm not sure on the author's approach in this case, but here's a live coding video of Inigo Quilez going over the basics of creating an eye in GLSL, he seems to

I'm not sure on the author's approach in this case, but here's a live coding video of Inigo Quilez going over the basics of creating an eye in GLSL, he seems to take the hand-editing route http://www.youtube.com/watch?v=emjuqqyq_qc http://www.youtube.com/watch?v=emjuqqyq_qc (You can see some more of his stuff on http://shadertoy.com/user/iq http://shadertoy.com/user/iq - his shader-writing skills are pretty incredible)