Again, requested by DragonKiller249
For this tutorial, you can use any brushes.

Step 1
Select the pupil of the eye.
We will be shading that part
For this tutorial, I'll be using this:

Step 2
Colour the pupil from black or the darkest colour of the eye until the lightest colour or white
It should look like this:

Step 3
Blur everything

Step 4
Add another layer and change the 'Normal' to 'Overlay'
Colour the eye again with either an even lighter colour or white

Step 5
Add another layer and change it from 'Normal' to ' Add'
Decorate the pupil however you like.
If you have no idea how you want decorate it, choose the stamps and decorate it anyway you like.
By the en, it should look like this

Hope it's helpful