Archive notice: This article was originally published on February 9, 2017. Links and embedded videos are preserved as part of the historical record.
In this tutorial, creature and character artist Jason Hill explains methods for creating an eye in ZBrush. You can also find a written version of the tutorial on his blog. Jason goes through all the steps, beginning with references, through modeling and sculpting, to texturing and rendering. In this case, the artist works with KeyShot for rendering, but you can also use any other ray-trace renderer. By the way, the files are also available as a free download:
Download & references
You can download the eye here; Jason Hill has put together a pin for references, which you can find here.