I didn't really beef up the blue but I did do a curves adjustment that did add contrast and in turn make them more blue.
I take the lasso tool and circle the eyes, then ctrl J for a new layer with just them, then a curves adjustment to taste, then I sharpen them at 132/.6/4 again, to taste and then I apply a mask and clean up any edges that look bad from my selection. You can also adjust the color of the eyes on this layer.
I don't do as good of a job as some. Some people can really get them sparkling. Here is one of my son, who has totally different colored eyes. It is amazing these two are twins
