I don't know if this is what you seek but you can create a Dynamic Plugin layer with the Liquid Metal value. It has a brush with some nice effects emulating metal, chrome, etc. But if the veins you are painting are very thin this effect may not work well. Anyway you can play with the shadows in the eyes, silver is a reflective surface and should reflect its surroundings. You can make lines along the vein reflecting the white part of the eye, a bit of the pupil, eyelash... Just look how anything shiny and round reflects light and things (a ring, a needle)
Hope this helps
Cheers!