If your using photo shop the first thing to do is free hand lasoo around the whites of the eyes including iris and pupil. Then with both eyes selected add an level adjustment layer and pull in the highlights slightly to whiten.
Then select both iris's and pupils and in a curves adjustment layer adjust to desrired colour and saturation.
With a small soft brush select a white colour and freehand flecks into the iris. Use the blur or smudge tool to soften the edges and adjust the opacity untill they are barely visable maybe 8 %
Then select the black and shade the pupil and line around the edge of the iris. Again use the opacity to merge this into the eyes.
Then sharpen
Hope this helps