I'm not a big fan of using realistic eyes, they look great but they are more difficult to use in animation.

To use them you must use overlay images for each frame. It may even be necessary to create a face with empty sockets to place the eyes behind it.

I find more easier to move the iris of basics eyes in the with area and filling the void with white color. It is much faster and simpler.

In any case, here you have this visual tutorial. Mr. Frixs say bye.