With the selection still active make sure the reflection layer is selected and press ctrl+j (layer via copy).  Hide or delete the original reflection layer.  Now click on "Add Layer Mask' to the new reflection layer.  With the new reflection layer selected select the Channels tab and select the New Reflection Layer Mask.  Select a radial gradient that goes from white to black and then draw a line with the mouse from the center of the pupil to the edge of the iris.If required you can use the brush to paint with either white to show more of the new reflection layer or black to hide more.  By hiding or showing the New Reflection Layer Mask you can see the effect your changes are having on the source image.

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