Here is an awesome guide to sculpting an eye in ZBrush by Mike Defeo, a sculptor whose specialty lies in translating 2D character designs into fully-fledged 3D models. The artist spent a lot of time at Blue Sky Studios bringing countless characters to life for Ice Age, Robots, Rio, Epic and other projects.  

Michael left the studio in 2010 to pursue his dream of working in Paris and landed a job at Illumination Entertainment, where he worked on characters for Despicable Me, The Lorax, Minions and The Secret Life of Pets.