Hey together this is my first post here. And while I am in the process of creating an eye. It should be an eye for a cat, now my question is the ires of the cat how I get it. Do you have any ideas how I can create it ? I already get the normal eyes of Iris from humans.
I am a total beginner in ZBrush 
Hello @The_Virus
Are you asking how to create an image of the eye, or how to apply that image to a mesh in ZBrush?
You can use an existing image, or you can paint one in an image editor (or Zbrush!). Once you have a texture, you can import it into ZBrush, and use Spotlight to paint it onto an eyeball as Polypaint. Here’s a video of Michael Pavlovich using Spotlight to texture a creature eyeball:
If you can narrow your question down into the more specific aspects of what you want to do, we could give you some less general advice.
Good luck! 