Simply append the asset you need: 

Either append (file/append/ ... locate the blend-file from this product) the sphere-object if you need a spherical eye, or you have your own geometry and need to append the material, or the node.

It is important, that your eye has scale applied, so that no matter what size it has, its scale xyz values are [1,1,1]. Distortions occur if the scale differs too much from 1.

Tipps:

• adjust the values from top to bottom
  
  
• as vector input use object coordinates from Input>textureCoordinates>Object to get the iris oriented in the z-direction of your mesh. If you want to animate the eye along the mesh surface choose a control object in the selector of the texture coordinate-cyclesnode
  
  
• use the homogenityvalue if the stretch value stretches the noise too much
  
  
• the depth might lead to strange results when applied to a stretched pupil. Handle with care, as the depth is just meant to fake some refractive behaviour of the eye.