When making eyes, I find the important question is always "how lazy do I feel today?"  I can either paint my own irises, or I can download some off the internet.  In this instance I have found some nice trout eyes, but they are very definitely trout eyes.  My sculpture isn't a trout.

In fact I nearly always make my own irises, because they're easy and fun to do.  These ones have a thick layer of iridescent medium, with purple and yellow glaze on top.  The colour and shape are loosely based on squid eyes.

Normally I make the lens of the eye using transparent acrylic cabochons, which you can get from places that sell jewelry supplies.  In this case I've cast my own resin lenses, because I need larger ones than are available from the jewelry supplier.  Honestly, I don't recommend casting resin lenses if you don't have to because getting the air bubbles out is a major pain in the backside.  I've found you have to heat up the resin before you use it, which makes it runnier and thus allows trapped air bubbles to escape.

I painted black pupils directly onto the resin lens, and once that dried I used Selleys' All Clear sealant to stick the lenses to the irises.  The key thing here is to apply a good thick layer of All Clear - and I'm talking half a centimeter/quarter of an inch here - and then press the lens down to squeeze any air bubbles out of the sealant.  Any clear glue or sealant will work for this, I just used the All Clear because I happen to have some.

Lastly, I put a sclerotic ring around the eyes, and then they're all ready to go.