The Power of Gray - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 152

Figure 2.79 Paint in black on a white layer mask to remove unwanted areas and reveal
the pupil.
7. Change the blend mode of the eye detail layer to Hard Light, and lower the opacity
to taste. In this example I lowered the opacity to 50% ( Figure 2.80 ) .