I've played with this in a different context (not eyeballs) ... and never found an epoxy I was happy with. I did find a Jewelers resin that dries clear, however. It's also less toxic than epoxy ... which was an added plus for me.
It's called ice resin and you can read more at www.iceresin.com
. I've never found it locally, and ended up ordering mine from artbeads.com for the free shipping.
While I've never cast printed eyeballs using ice resin, I have hand painted eyes on rolled plaster balls and then put a coat of ice resin on them to make them look wet and shiny. They're very effective.