Thanks so much guys, I'm truly grateful for the support.
Fiendishwizard- I use eye blanks which are resin half spheres to sculpt around. They are 27mm in diameter, I believe. For this one, I used spheres with a bit of retinal bulge.
I used to use small glass christmas ball ornaments, but the chrome was a bit too distracting as the sculpt progresses, so I make the resin ones now.