Eyes are special.

The eyeball, the iris, the pupil, the cornea, all need to be looked into, and all attribute to the final result, and some will certainly interfere with each other.
Do all need SSS?

Be certain to put them all in different SSS groups or you can get some nasty blue artifacts.
Have not seen a tut on the subject yet.

I think BB had en eye setup on his site. You could check there and build from there on?

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!